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Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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CHAPTER FIVE

Ecosystem Services in the Gulf of Mexico

INTRODUCTION

In Chapter 2 we outlined the general concept of ecosystem services and the basic principles and challenges of applying an ecosystem services approach to damage assessment for an event of the magnitude and duration of the Deepwater Horizon (DWH) oil spill. Chapter 3 explored the concept of resilience in the context of ecosystem services and the challenges faced by managers in attempting to restore or increase the resilience of the Gulf of Mexico (GoM) ecosystem. Chapter 4 reviewed the response technologies used during and after the DWH oil spill and their impacts on GoM ecosystem services. This chapter brings the discussion of ecosystem services into focus by examining in more detail the specific ecosystem services provided by the GoM. The chapter begins by considering the characterization of GoM ecosystem services within a geospatial context and how ecosystem services vary as a function of scale and in response to changes in the physical and environmental setting.

The remainder of the chapter is dedicated to presentation of four case studies representing each of the primary ecosystem service types—supporting, regulating, provisioning, and cultural—and chosen to capture the opportunities and challenges that emerge when applying the ecosystem services approach to assessing the impact of the DWH spill on the GoM. For each of these case studies, the committee identifies key ecosystem services, considers how they may have been impacted by the DWH oil spill, examines methods for taking baseline measurements, and explores the adequacy of existing baseline data for the GoM. Additionally, the committee offers suggestions for additional measurements that can enhance an ecosystem services approach to damage assessment (Tables 5.5, 5.6, 5.7, and 5.8).

ECOSYSTEM SERVICES IN THE GULF OF MEXICO

As a starting point for examining ecosystem services specific to the GoM, the committee utilized a list of GoM ecosystem services that was developed by a panel of regional experts during a workshop convened in Bay St. Louis, Mississippi, in June 2010 (Yoskowitz et al., 2010). The workshop panel, composed of representatives from academic institutions, nongovernmental organizations, the private sector, and state and federal agencies, defined ecosystem services as the “contributions from GoM marine and coastal ecosystems that support, sustain and enrich human life.” As shown in Table 5.1, the panel identified 19 ecosystem services provided by the GoM natural infrastructure and grouped them under the four primary types of ecosystem ser-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

vices (supporting, regulating, provisioning, and cultural) defined by the Millennium Ecosystem Assessment (MEA, 2005).

TABLE 5.1 Gulf of Mexico Ecosystem Services by Millennium Ecosystem Assessment Category

Supporting services

Nutrient balance

Hydrological balance

Biological interactions

Soil and sediment balance

Regulating services

Pollutant attenuation

Water quality

Gas regulation

Climate regulation

Hazard moderation

Provisioning services

Air supply

Water quantity

Food

Raw materials

Medicinal resources

Ornamental resources

Cultural services

Aesthetics and existence

Spiritual and historic

Science and education

Recreational opportunities

Panelists in the Bay St. Louis workshop (Yoskowitz et al., 2010) recognized that the coastal and marine habitats of the GoM also constitute a natural infrastructure that contributes to the provisioning of ecosystem services. When ecological production functions are not well understood, integrated assessments of ecosystem services tend to use natural structures such as habitats to map the complex interactions of different components of the ecosystem. The scale for assessing an ecosystem service must be determined by the threshold at which changes in ecosystem functioning (or its habitats) can be detected (measured) and at which the ecosystem sustains functions that contribute to its resilience (as discussed in Chapter 3). Table 5.2 organizes a number of important GoM ecosystem services by habitat, which could be used to guide efforts in delineating and determining changes in ecosystem services after the DWH oil spill.

Ecosystem services can also be classified according to their spatial characteristics (see Table 5.3). Each of the 19 ecosystem services provided by the GoM can be mapped to at least one of the five different spatial classes (global nonproximal, local proximal, directional flow-related, in situ or point of use, and user movement-related) proposed by Costanza (2008). For example,

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

TABLE 5.2 Synthesis of Services Provided by the Gulf of Mexico by Service Category and Habitat

Ecosystem Service Category Habitat Example in the GoM
Supporting services  

Soil and sediment balance

Brackish marsh

Upper Barataria estuary, Louisiana

 

Dunes/beaches

Barrier islands, Texas

 

Forested coastal ridge

Chenier Forest/Woodlands, Louisiana

 

Intertidal sediments

Mud flats in Laguna Madre, Texas

 

Subtidal sediments

Widespread throughout the Gulf

 

Mangroves

Everglades, Florida

Nutrient regulation

Brackish marsh

Upper Barataria estuary, Louisiana

 

Freshwater marsh

Rockefeller State Wildlife Refuge, Louisiana

 

Macroalgae

Floating and beached Sargasso

 

Swamp/bottomland hardwood

Maurepas Swamp, Louisiana

 

Subtidal sediments

Widespread throughout the Gulf

Regulating services  

Water quality

Oyster reef

Mobile Bay, Alabama

 

Seagrass

Redfish Bay, Texas

Hazard moderation

Oyster reef

Barataria Bay, Louisiana

 

Salt marsh

Mississippi River Delta, Louisiana

 

Freshwater marsh

Barrier island freshwater marshes, Texas

 

Swamp/bottomland hardwood

Sabine River floodplain swamp, Texas and Louisiana

 

Dunes/beaches

South Pacific Island, Texas

 

Forested coastal ridge

Chenier Forest/Woodlands, Louisiana

 

Mangroves

Everglades, Florida

Provisioning services  

Food

Oyster reef

Galveston Bay, Texas

 

Seagrass

Laguna Madre, Texas

 

Open water

Widespread throughout the Gulf

 

Offshore shoals and banks

Sabine Bank, Texas and Louisiana

 

Subtidal sediments

Widespread throughout the Gulf

Raw materials

Oil and gas fields/reservoirs

Shelf/slope of central, western planning areas of the Gulf

 

Offshore shoals and banks

Sabine Bank, Texas and Louisiana

Cultural services  

Aesthetics and existence

Spiritual and historic

Shell middens throughout the Gulf

 

Coral reefs

Florida Keys National Marine Sanctuary, Florida

 

Dunes/beaches

St. George Island State Park, Florida

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×
Ecosystem Service Category Habitat Example in the GoM

Recreational opportunities and tourism

Coral reefs

Florida Keys National Marine Sanctuary, Florida

 

Salt marsh

Northern Barataria Bay, Louisiana

 

Forested coastal ridge

Grand Isle, Louisiana

 

Intertidal sediments

Bays and estuaries anywhere in the Gulf

 

Open water

Widespread throughout the Gulf

 

Offshore shoals and banks

Florida Middle Grounds, Florida

Science and Education

 

Widespread throughout the Gulf

SOURCE: Modified from Yoskowitz et al., 2010.

TABLE 5.3 Gulf of Mexico Ecosystem Services by Spatial Characteristics

Global nonproximal (does not depend on proximity)

Climate balance

Gas balance

Air supply

Existence

Spiritual and historic

Local proximal (depends on proximity)

Hazard moderation

Pollutant attenuation

Biological interactions

Directional flow-related: flows from point of production to point of use

Water quality

Water quantity

Sediment balance

Nutrient balance

Hydrological balance

In situ (point of use)

Soil balance

Food

Raw materials

Ornamental resources

User movement-related: flow of people to unique natural features

Medicinal resources

Recreational opportunities

Aesthetic

Science and education

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

a service such as gas balance (an intermediate input to climate regulation) is classified as “global nonproximal” because carbon sequestration occurs across the entire GoM and beyond. “Local proximal” services, on the other hand, are dependent on the spatial proximity of the ecosystem service to the human beneficiaries. For example, “hazard moderation” requires that the ecosystem service be proximal to the human settlements and assets being protected. “Directional flow-related” services are dependent on the flow from upstream to downstream, as is the case for water quality and water quantity.

An examination of the spatial relationships of ecosystem services highlights the need to identify and manage natural infrastructure at scales that improve its ability to withstand chronic or acute impacts, such as those associated with the DWH oil spill. If the natural infrastructure is damaged, then human communities that benefit from the services provided by these ecosystems will likely become more vulnerable, therefore decreasing their overall wellbeing and resilience. Any degradation of the ecosystem structure and function may lead to a reduction in the supply of the essential services that will be needed to help communities build the resilience needed to withstand damages and recover after the spill (see discussion of socioeconomic resilience in Chapter 3). Examples of spatially specific benefits in the GoM region that could be severely impacted by an oil spill include storm mitigation by coastal wetlands and food provisioning by commercial fisheries. Consideration of the spatial characteristics of ecosystem services is important not only when assessing damages, but also when deciding which services to restore. Tradeoffs will be necessary, and recognizing which communities or sectors may benefit (or lose) from restoration efforts will be useful when priorities are set by the Trustees and stakeholders.

CASE STUDIES

The committee conducted four case studies to explore specific GoM ecosystem services in detail, to highlight some of the opportunities and challenges that emerge when applying an ecosystem services approach to damage assessment, and to demonstrate how to apply such an approach under various conditions and across wide levels of understanding regarding the services in question. These conditions and levels include the amount and utility of available data, the value of the service in market and nonmarket terms, and the range of the impacts of the spill on the services. In addition, the selected ecosystem services were considered in the context of the linkages between ecosystem services and the constituents of well-being identified in Chapter 2 (see Figure 2.1).

Coastal wetlands, which cover a large region in the northern GoM, are the subject of the first case study. Half of the nation’s coastal wetlands are found along the GoM, and, of these, approximately 40 percent are in Louisiana. Unfortunately, many wetlands were among the closest land points (only about 40 miles) from the Macondo well (NOAA, 2012b). Coastal wetlands, including salt marshes and mangrove plant communities, provide a wealth of supporting, regulating, provisioning, and cultural services that include maintenance of soil and sediment (shoreline stabilization), regulation of nutrients and water quality, provisioning of food, recre-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

ational opportunities, and hazard moderation (Barbier et al., 2011; Shepard et al., 2011). This case study focuses primarily on the regulating service of hazard moderation (specifically storm mitigation) to illustrate the opportunity that exists in using the ecosystem services approach when the underlying ecosystem science and the particular ecosystem service are well known and supported by a rich literature. The ecosystem service of storm mitigation also benefits from having been monetized—that is, the costs of storm damage and reductions in losses due to wetland buffers can be quantified.

The second case study focuses on fisheries, a provisioning service with a rich literature about its valuation and assessment. In recent times, this service has been considered to be a good candidate for a holistic integration of management at an ecosystem scale that includes both ecological and human components. Although the field has been developing this integration by promoting an ecosystem approach to fisheries management, it does not yet consider ecosystem services as a guiding principle. Fisheries, however, offer many examples of quantification of human impacts on the ecosystem structure and of ecological and economical productivity. This case study specifically explores the provision of seafood by the GoM and how the ecosystem services approach may help to quantify the possible impacts of oil spills on seafood provision.

Bottlenose dolphins were chosen as the subject for the third case study for numerous reasons, including their role in three of the four types of ecosystem services—regulating, supporting, and particularly cultural. This case study allowed for the exploration of approaches to estimating the value of passive use and existence—a key, but difficult-to-establish, metric for cultural ecosystem services. The stranding of many dolphins in the GoM before, during, and especially after the DWH spill has stimulated considerable public concern, which speaks to our cultural needs and sensitivities regarding their value as an ecological resource and ecosystem service.

Bottlenose dolphins are capable of self-recognition, which ranks them highly on a cognitive scale (Reiss and Marino, 2001). As apex predators, a role they share with humans, they play a role in regulating the GoM food web and their health and well-being serve as important indicators of the health of the GoM and oceans in general. More is known about this species than virtually any other cetacean. The world’s longest-running study of a wild dolphin population, spanning five generations, focuses on Sarasota Bay in the eastern GoM (Wells, 2003). Their position as the most studied and arguably the most popular and charismatic marine mammal makes them a centerpiece for conservation science, education, and ecotourism.

Finally, the deep GoM was selected as the subject for the last case study in part because of its location with respect to the DWH blowout and spill. The deep sea was also selected because of increasing concern about the risk posed by the energy industry’s activities as it employs the cutting edge of engineering in the most poorly understood of the impacted habitats. The biota of the surrounding seafloor at 1,500-m depth and of the water column through which a plume of hydrocarbons and dispersants flowed received the most immediate impact of the uncontrolled discharge. Although there has been some habitat mapping of the deep GoM, the data are quite sparse and the ecological consequence of a spill is incompletely understood.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Wetlands

Introduction

Coastal wetlands, including salt marshes and mangroves, provide a wealth of supporting, regulating, provisioning, and cultural services that include soil and sediment maintenance (shoreline stabilization), nutrient regulation, water quality regulation, provision of food and other biological resources, recreational opportunities, and hazard moderation (Barbier et al., 2011; Shepard et al., 2011). The marshes of the Mississippi River Delta comprise almost 40 percent of the coastal wetlands in the 48 contiguous states, support 30 percent of the nation’s commercial fishery production, and protect important oil and gas reserves and refineries (Mendelssohn et al., 2012). During the DWH oil spill, coastal salt marshes were significantly affected, with 1,100 linear miles of wetland impacted at some time during the event (NOAA, 2012b). Crude oil can smother vegetation by coating leaf surfaces and can cause toxic effects, particularly from the light fractions of the oil that are more water soluble.

With wetlands, the values of some of its ecosystem services, such as storm mitigation, can be quantified within an order of magnitude, while for others, such as nursery habitat for commercial marine resources, the values are much more difficult to quantify. The following discussion focuses on hazard mitigation because it represents an example of ready application of the ecosystem services approach using the existing knowledge base.

Regulating Services

Hazard Moderation Several wetland characteristics are positively correlated with the regulating ecosystem services of both wave attenuation and shoreline stabilization, including vegetation density, biomass production, and marsh size (Shepard et al., 2011).

The topography of wetlands (including plant architecture) provides enhanced friction, which tends to decrease wind speed, wave height, storm-driven steady currents, and stormsurge height. Wetlands can also decrease tropical storm intensity by inhibiting the transfer of heat from the ocean to the atmosphere. It is this latter energy transfer that serves as the basic engine that drives a tropical storm.

Reduction of wave energy depends on the structure of the plant canopy, its height and density, and the cross-shore and along-shore extent of the wetland (Koch et al., 2009; Krauss et al., 2009; Massel et al., 1999; Narayan and Kumar, 2006; Shepard et al., 2011; Vosse, 2008). The velocity of water traveling within a plant canopy is relatively lower than above the canopy. Canopy height in relation to water depth is relevant because water flowing through the vegetation encounters a higher friction than does the water above the vegetation. Therefore, the total friction in the water column will change with the depth of vegetated and nonvegetated areas. Because a mangrove canopy is taller and exerts more drag than a salt marsh community, mangroves are more effective at reducing water inflow and waves than are salt marshes. Quartel et al. (2007) suggested that the drag force exerted by a mangrove forest can be approximated by

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

the function CD = 0.6e0.15A, where CD is the coefficient of drag and A is the projected crosssectional area of the submerged canopy. For the same muddy surface without mangroves, the drag is a constant 0.6. Mazda et al. (1997) observed that a 100-m-wide strip of mangrove forest was capable of reducing wave energy by 20 percent. Reduction in water levels across a mangrove area in Florida was 9.4 cm/km (Krauss et al., 2009).

Wave energy is also affected by topography. In a modeling study of sea level rise and storm surge across the Louisiana coast, Vosse (2008) found that when the relative land elevation was decreased by 20 cm and 50 cm, wave heights increased 5–10 cm and 10–20 cm, respectively, across the model domain. The conclusion is that friction by the plant canopy dissipates energy and reduces wave heights, but the effect of the wetland surface depends on water depth. Consequently, the relative elevation of a coastal wetland, not simply its presence or absence and structure, is a determinant of its effectiveness in storm hazard mitigation.

Like waves, storm surge can be reduced by the presence of wetlands because of the increased dissipation. The U.S. Federal Emergency Management Agency (FEMA) provides estimates of the impact of various types of wetland vegetation on frictional dissipation (FEMA, 1985). United Research Services (URS) used the FEMA estimates and a well-validated numerical model to examine the impact of vegetation on surge height. It found a 25 percent reduction in the inland surge simply by assuming the marshland was composed of long grass instead of short grass (Ayres Associates, 2008). Along with these reductions in surge height are substantial secondary benefits. For example, the current velocity is reduced and so is the wave height because larger waves require higher surge, all else being equal. Finally, a reduction in wave height reduces the wave setup, which is a contributor to the surge.

Although there is ample evidence that wetlands reduce surges and waves, the evidence is less clear for winds. One problem is that storm winds (as well as surges and waves) can severely alter the vegetation during the course of a storm. Dingler et al. (1995) discuss this issue, using data collected during Hurricane Andrew, which hit the Mississippi River Delta in 1992. They found that wind dissipation was higher over the wetlands than over the ocean, but only when wind speeds exceeded 20 m/s. This effect occurred despite the fact that the wetlands in the study area were composed primarily of Spartina and bulrushes, which would have “flattened” during the stronger winds. Somewhat in contrast to Dingler et al. (1995), FEMA (1985) suggested factors that show a substantial increase in wind dissipation over open-ocean values for all types of wetlands and wind speeds. In total contradiction of the other two researchers, Speck (2003) showed a decrease in dissipation with rising wind speed above 1 m/s over 4-m reeds compared to open ocean. In short, no consistent picture emerges from the research regarding wind dissipation, which is no doubt partially due to the facts that the vegetation type in these studies was highly variable and that the dissipation effectiveness varies over the course of a storm as vegetation is damaged by wind, wave, and current.

Wetlands may also have an effect on tropical storms by mitigating storm intensity. As explained by Emanuel (1987), the intensity of a tropical cyclone is driven by a Carnot cycle (a thermodynamic cycle) that requires warm, humid air near the sea surface. Anything that disrupts that supply will reduce storm intensity. Wetlands clearly have that potential, especially if they contain a high percentage of vegetation. Cubukcu et al. (2000) used a numerical model to ex-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

amine the effects of land and found a significant weakening in the surface winds in large part because the storm entrains much drier air. However, Shen et al. (2002) showed that not much water (0.5 m deep) was required to substantially counter this weakening effect, a finding that supports anecdotal evidence from numerous tropical storms that have cut across the wetlands of southern Florida without losing a great deal of intensity.

In summary, the general trend is for wetlands to reduce the severity of a storm and its associated wind and waves through numerous physical processes, most of them related to the enhanced friction, which serves as an energy sink.

Changing Baselines

Although the DWH oil spill had multiple impacts on wetlands (discussed below), the most serious threat to GoM wetlands is their inability to keep up with relative sea level rise (Boesch et al., 1994). The reasons for this inability have been discussed in numerous publications (Boesch et al., 1984; Britsch and Kemp, 1990; Day et al., 2009; Dokka et al., 2006; Mallman and Zoback, 2007; Meade, 1982; Reed, 2002; Reed and Wilson, 2004; Turner, 1997). One notable problem is a reduction in sediment supply caused by the construction of levees and dams. Periodic overbank flooding supplied large pulses of sediment to marshlands behind natural levees, but these sediment supplies have been all but eliminated by the hardening and extension of the levees for flood control and navigation. GoM coastal wetlands have also been extensively dredged to provide access to oil and gas platforms, which has seriously degraded freshwater wetlands by providing a conduit for saltwater intrusion (Turner et al., 1982). The piling of dredge spoils on the banks of wetlands adjacent to the canals has also disrupted the natural flow of surface water and sediments across the marshes.

The Mississippi River Delta consists of an estimated 25,000 km2 of wetlands, open water, distributaries, and beach ridges. Of the remaining coastal habitat, there has been a net loss of approximately 4,800 km2 over the past century (Day et al., 2005). The loss rate decreased from a high of about 80 km2/year in the 1970s to about 45 km2/year by the turn of the century (Barras et al., 2003; Bernier et al., 2007). It is not clear if the recent decline in loss rate is due to variation in sea level rise (e.g., Bernier et al., 2007; Kolker et al., 2011), subsidence (e.g., Morton et al., 2002), the resolution of GIS technology, the reduction of dredging activities in the marshes, or other factors. The National Oceanic and Atmospheric Administration (NOAA) gauge on Grand Isle, Louisiana, has registered a variable, long-term relative rate of sea level rise of 6.7 mm/year (Figure 5.1). More recently, a 2005 coastwide analysis indicated that more than 4,714 km2 of the pre-storm coastal wetland area experienced a substantial decline in vegetation density and vigor after Hurricane Katrina, with the majority of persistent damage through November 2006 in the western areas (Steyer, 2008). In addition, the background rate of marsh loss is not uniform across the coast, and is especially acute in the region most impacted by the DWH oil spill (Figures 5.2 and 5.4).

Current literature supports the conclusion that wave and storm surge attenuation and damage avoidance are related to wetland area, either nonlinearly with diminishing returns

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

image

FIGURE 5.1 Linear regression of mean (±1 SD) annual sea level at Grand Isle, Louisiana (NOAA station 8761724). NOTE: Annual means were computed from monthly means. SOURCE: http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8761724.

to scale (Barbier et al., 2008) or linearly (Costanza et al., 2008). Consequently, change in total wetland area is the most direct and practical measurement of change in ecosystem services in Gulf Coast wetlands. To quantify changes in wetland area, remote sensing is a highly effective method for analyzing estuarine and coastal landscapes (Kelly and Tuxen, 2009; Klemas, 2001; Phinn et al., 2000). Remote sensing is used to efficiently map, monitor, and detect changes in wetlands (Ramsey et al., 2011; Zhang et al., 1997). New satellites carry sensors with spatial resolutions of 1–5 m and spectral resolutions of 200 nm, providing the capability to accurately detect changes in coastal habitat and wetland health (Bourgeau-Chavez et al., 2009; Klemas, 2001, 2011; Ozesmi and Bauer, 2002).

The classification of wetland areas and plant communities is also improving as data from satellites are combined with those collected from fixed-wing aircraft. LiDAR (light detection and ranging), an optical system that can measure the distance to a target and other properties using pulses from a laser, is one of the sensors now commonly used on fixed-wing aircraft. This tool is used to construct digital elevation models and to develop digital profiles of plant canopies (e.g., Omasa et al., 2006). Classification schema based on combinations of these data

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

image

FIGURE 5.2 Land loss change in coastal Louisiana. SOURCE: http://www.nwrc.usgs.gov/upload/landlossllX17.pdf.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

sources can delineate wetland plant communities with a high degree (76–97 percent) of accuracy (Gilmore et al., 2008), and temporal changes can be resolved with repeated measures. The vertical accuracy of airborne LiDAR systems is probably not great enough to detect changes in elevation that are less than 5–10 cm (Hladik and Aber, 2012; Montané and Torres, 2006), but ground-based LiDAR scanners can accurately profile the elevation (millimeter accuracy) of a limited marsh surface area (1- to 10-m scale) (Boehler et al., 2003).

There are also episodic changes due to storms (Steyer et al., 2010) and now possibly to the DWH oil spill. Distinguishing the background trends and noise associated with storms, droughts, and other factors from oil-spill-related effects will be challenging (Figure 5.5). Four detectable oil responses are possible, assuming none is positive. One possible response is no response; that is, the wetland area continues along a declining, unstable baseline because of other forces (line A in Figure 5.3). A second possible response is a long-lasting episodic increase in marsh area loss (line B in Figure 5.3), and a third response is a loss of area followed by a recovery or restoration to a previous (lower) baseline followed by subsequent decline or stability (line C in Figure 5.3), depending on the type of restoration. Finally, a hypothetical stimulation of plant growth by light oiling and short-term marsh expansion (still to a lower baseline) is depicted by line D in Figure 5.3. Detection of these alternatives would not be possible without

image

FIGURE 5.3 Hypothetical background noise and trend in wetland area with shocks and the possible responses following exposure to DWH oil and restoration. Lines A, B, and D represent the potential trajectories wetland areas may take because of the impacts of the spill, and line C represents the possible trajectories post-restoration. SOURCE: Committee.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

image

FIGURE 5.4 A Landsat Thematic Mapper image of study area depicting locations and dates of ground observations of oil contamination from the DWH oil spill. SOURCE: Reproduced with permission from Ramsey et al. (2011).

image

FIGURE 5.5 Dark grey denotes the extent of the oil slicks in the vicinity of Barataria Bay, Louisiana, based on satellite observations made on (a) May 23, 2010, and (b) June 4, 2010. SOURCE: Reproduced with permission from Ramsey et al., (2011).

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

a monitoring network and pre-spill data, and subtle impacts will be challenging to detect even with a ground network and remote sensing. The effort will require sampling large areas with sufficient temporal frequency and spatial detail to resolve the changes. Fortunately, the tools exist and the groundwork is in place.

Finding 5.1. Wetlands provide a wealth of ecosystem services, ranging from fishery production to hazard mitigation (particularly storm surge protection). Storm protection by wetlands is achieved through several mechanisms, most of which ultimately trace their origins to the increase in frictional resistance to the storm afforded by vegetation..

In 1990, the U.S. Congress enacted the Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) in response to ongoing wetland loss along the Louisiana coast. CWPPRA authorized funding in 2003 for the Louisiana Office of Coastal Protection and Restoration (OCPR) and the U.S. Geological Survey (USGS) to implement a Coastwide Reference Monitoring System (CRMS) as a mechanism to monitor and evaluate the effectiveness of CWPPRA projects across the region (Steyer et al., 2003). As a part of the monitoring program, reference sites were selected to establish the status and trends of existing wetlands. Three hundred and ninety (390) sites with a fixed annual sampling design were approved and secured for CRMS data collection. These sites located within nine coastal basins covering the entire Louisiana coast are sampled annually using a fixed design (Figure 5.4). Sample collection from the ground began in 2005 and will be an important complement to remote sensing techniques. Few of the CRMS sites were impacted by oil (Brady Couvillion, USGS, personal communication, 4/14/2011). Nevertheless, the distribution of sites provides important information about the status and trends of existing wetlands. Data collected at each site include information on sediment accretion and plant community metrics.

DWH Spill Impact on Wetlands

A review of the effects of oil spills on wetlands in general can be found in Mendelssohn et al. (2012). Largely, the sensitivity of vegetation and soil organisms to hydrocarbon exposure depends on the type and concentration of hydrocarbon (Cermak et al., 2010). The lighter fractions and especially the aromatic hydrocarbons are more acutely toxic than are the heavier fractions (Chaîneau et al., 1997; Ziółkowska and Wyszkowski, 2010). Toxicity increases with the number of aromatic rings on the molecule (Baek et al., 2004). There are toxic effects to marsh vegetation from the light hydrocarbons in crude oil and smothering effects from fouling of leaf surfaces from heavy crude (Pezeshki et al., 2000).

A number of field and greenhouse studies of oiled marshes have been conducted. One study found that, although both diesel and heavy oil significantly affected the salt marsh vegetation, 1,000 parts per million (ppm) of diesel alone resulted in >90 percent mortality of aboveground biomass of smooth cordgrass, Spartina alterniflora. Plants took much longer to recover from exposure to diesel fuel than from exposure to crude oil (Lin and Mendelssohn, 2003). In

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

contrast, Lippencott (2005) observed 90 percent survival of saltmeadow cordgrass, Spartina patens, in plots containing sediments with <12 percent petroleum hydrocarbons, and DeLaune et al. (1984) showed that direct oiling of a Louisiana marsh caused no reduction in macrophyte production or oil-induced mortality for the marsh macrofauna or meiofauna. Similarly, salt marsh vegetation in Texas recovered within 1–2 years after exposure to crude oil (Webb et al., 1985). A greenhouse study of the effect on Spartina alterniflora of chronic exposure to aromatic hydrocarbons found that application of 3.3 g C m-2 d-1 unexpectedly stimulated plant growth, while application of 33 g C m-2 d-1 inhibited growth (Li et al., 1990).

Addition of heavy oil to a Spartina salt marsh in the autumn resulted in high concentrations of the polycyclic aromatic hydrocarbons phenanthrene, chrysene, and fluoranthene in sediment and benthic animals, but hydrocarbon concentrations rapidly decreased over the next 20 weeks (Lee et al., 1981), probably because of degradation and dispersal of the hydrocarbons. Hydrocarbons are degraded primarily by bacteria and fungi, with prior adaptation to hydrocarbons by microbial communities increasing hydrocarbon degradation rates (Atlas, 1981; Leahy and Cowell, 1990), as is likely the case in the Gulf Coast region where navigation and oil seeps are chronic sources of hydrocarbons. Enhancement of hydrocarbon degradation by rhizosphere-associated bacteria also appears to be a significant process (Daane et al., 2001; Lippencott, 2005).

Mendelssohn et al. (2012) and Silliman et al. (2012) discussed impacts specific to the DWH oil spill. The expectations for long- and short-term effects of oil fouling of marshes depend on the aerial extent of the exposure and its magnitude. Acute effects of oil fouling of marshes appear to be confined to the margins of bays, canals, and creeks in a limited area (Figures 5.4 and 5.5) (Ramsey et al., 2011; Silliman et al., 2012). Although oil from the spill impacted about 690 km of shoreline vegetation from the Chandeleur Islands to Point Au Fer in Louisiana, the oil was already weathered by the time it reached the shore, so initial considerations were physical coating and hypoxia (Mendelssohn et al., 2012). Wetlands that were oiled include salt marshes, mangroves dominated by the black mangrove, Avicennia germinans, and marshes along the Mississippi River Bird’s Foot Delta dominated by the common reed, Phragmites australis.

Field surveys conducted between July 7 and August 26, 2010, in central Barataria Bay and the Mississippi River Bird’s Foot Delta of Louisiana, found that oiling in Barataria Bay marshes ranged from lightly oiled sections of stems of the predominant marsh plant species, Spartina alterniflora and Juncus roemerianus, to wide zones of oil-damaged canopies and broken stems, penetrating as far as 19 m into the marsh (Kokaly et al., 2011). The oil-damaged zone in Barataria Bay extended an average of 6.7 m into the marsh and usually more than 100 m parallel to the shore. Oil was observed on the marsh sediment at some sites, both above and a few centimeters below the water surface. The common reed, Phragmites australis, was the dominant vegetation in oil-damaged zones in the Bird’s Foot Delta. Oiling of the leaves and portions of the thick stems of P. australis was observed during field surveys. In contrast to the marshes of Barataria Bay, fewer areas of oil-damaged canopy were documented in the Bird’s Foot Delta. In both areas, oil was observed to be persistent on the marsh plants from the earliest (July 7) to the latest (August 24) surveys. At sites that were repeatedly visited in Barataria Bay over this time period, oiled plant stems and leaves, laid over by the weight of the oil, broke and were re-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

moved from the vegetation canopy, likely because of tidal action. In these areas, a zone of plant stubble 2–5 cm high remained at the edge of the marsh. Further signs of both degradation and recovery were observed and varied by site. Some oil-damaged sites experienced complete reduction of live vegetation cover and erosion of exposed sediments, while other damaged sites experienced regrowth of vegetation (Silliman et al., 2012).

Finding 5.2. Field surveys have been conducted to evaluate the damage to wetlands from the DWH oil spill, most of which is thought to be caused by physical coating and hypoxia. Those surveys identified sites where the vegetation had died in heavily oiled areas; sediment erosion often led to the conversion of once productive marshland to open water. However, in view of numerous studies that document a rapid recovery from oiling and a relatively low sensitivity of perennial marsh vegetation to hydrocarbons, marsh vegetation can be expected to suffer little or no long-term impairment from the spill in areas where roots and rhizomes survived the initial impact of oil fouling.

Seven months after oil from the DWH oil spill came ashore in the salt marshes of Bay Jimmy in northern Barataria Bay, Louisiana, the concentration of total petroleum hydrocarbons at a sediment depth of 2 cm was as high as 510 mg/g, causing almost complete mortality of Spartina alterniflora and Juncus roemerianus (Lin and Mendelssohn, 2012). Moderate oiling had no significant effect on Spartina (which was borne out by greenhouse studies confirming its tolerance to oil covering the shoot) but caused a significant decrease in live aboveground biomass and stem density of Juncus. Spartina was able to recover from complete oil coverage of shoots in 7 months. Penetration of the sediment significantly affected both species in greenhouse tests, which along with shoot coverage and recurring oiling explains the severe impacts to coastal marsh vegetation from the DWH oil spill (Lin and Mendelssohn, 2012). Some recovery has been noticed in oiled delta marshes at the mouth of the Mississippi and throughout Louisiana, but as of autumn 2011, most marshes had shown little recovery (Mendelssohn et al., 2012).

As discussed in detail in Chapter 4, cleanup activities after an oil spill can cause indirect effects (Table 5.4), including physical disturbance and compaction of vegetation and soil, which are detrimental to marshes (Pezeshki et al., 2000). Among the cleanup options, the strategies with the least risk and greatest reward are no response, bioremediation, burning, and vegetation cutting, depending on the type of sediment substrate and severity of fouling.

Where the vegetation has died in heavily oiled areas, sediment erosion will likely lead to the conversion of once-productive marshland to open water. However, in view of numerous studies that document a rapid recovery from oiling and a relatively low sensitivity of perennial marsh vegetation to hydrocarbons, marsh vegetation can be expected to suffer little or no long-term impairment from the DWH oil spill in areas where roots and rhizomes survived the initial impact of oil fouling.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

TABLE 5.4 Advantages and Disadvantages of Cleanup Techniques Used in Marshes

Advantages Disadvantages

No response

Minimal impact (if oil degrades quickly), no physical impact Potential oiling of birds or wildlife, oil may impact adjacent areas, heavy oils may degrade slowly or form asphalt

Vacuum/pumping

Can remove large quantities of oil Access/deployment of equipment, physical impacts

Low-pressure flushing

Assists in removal by herding oil, lifts oil off sediment surface Requires careful monitoring, pressure must be controlled, physical impacts (loss of sediment)

Burning

Potential to remove oil quickly, can minimize impacts from trampling Kills or damages oiled (burned) plants and associated fauna

Sediment removal

May be only remediation possible for heavily oiled sediments Can destroy the marsh, increased erosion potential, elevation changes may impede regrowth of plants, replanting necessary

Vegetation cutting

Preserves belowground plant parts, prevents oiling of birds May kill plant depending on species, potential for increased erosion, must be carefully monitored

Bioremediation

Great theoretical potential, low impact Potential for nutrient enrichment, may increase sediment hypoxia

SOURCE: Modified from Hoff (1995).

Storm Hazard Moderation: Ecological Production Functions and Valuation

Well-established relationships among plant canopy, plant height, plant density and extent, and topography relative to sea level can moderate the impacts of storms. These features of the plant communities across the wetlands collectively make up part of the ecosystem structure that utilizes the physical processes (ecosystem function) to provide the ecosystem service of storm hazard moderation. The ecological production function in this example specifies the output of ecosystem services (coastal protection) generated by the wetlands given its current condition (the state of the vegetation and topography) relative to its ecosystem function (storm mitigation). Knowledge of these relationships should allow for quantitative modeling of the capacity of wetlands to moderate storms.

The next step in the ecosystem services approach is to attempt to attribute a monetary value for this service. Two methods for doing so include quantifying the costs avoided, as in the case of storm mitigation, or the replacement costs, as in the case of engineered defenses.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Quantifying the avoided costs is probably the most common method used to value coastal protection (Badola and Hussain, 2005; Costanza et al., 2008; Danielsen et al., 2005; Das and Vincent, 2009). The value of coastal protection afforded by coastal wetlands can be estimated by finding the difference in likely damages to coastal communities from a storm event with intact coastal marshes versus an event with degraded or no coastal marshes, considering their relative capacities to absorb wave energy and reduce storm surges (NRC, 2011). Costanza et al. (2008) used this method and concluded that 60 percent of the variation in damage caused by 34 major U.S. hurricanes was explained by wind speed and wetland area in the swath of the storm.

The marginal value of a wetland varies with the level of economic activity in the path of an average storm—the higher the level of economic activity, the higher the costs avoided. A wetland’s marginal value is also inversely related to its size—the larger the acreage, the lower the marginal value of an additional acre of wetland. The estimated marginal value of wetlands in the Gulf Coast region after Hurricane Katrina was $4,363 ha-1. However, the marginal value of wetlands in the region varied greatly in an analysis by Costanza et al. (2008), from a low of $126 ha-1 yr1 in Louisiana to a high of $14,155 ha-1 yr1 in Alabama. This large range of values is partially an artifact of the areal extent of marsh versus the economic activity that it can protect.

The marsh’s effectiveness in moderating storms is determined not only by its size, but also by its biophysical condition. Fragmented marsh will not be as effective at reducing storm surges as will continuous marsh (Loder et al., 2009), but in current approaches to valuation only areal extent, not degree of fragmentation, is considered.

Finding 5.3. The ecological production function for storm mitigation from wetlands relates changes in wetland area to changes in coastal protection. The value of storm mitigation by wetlands can be measured using the avoided cost method, which assesses the benefits of maintaining an ecosystem that provides protection against storms, floods, or other natural disasters.

Natural Resource Damage Assessment

As discussed in the Interim Report (NRC, 2011) and in Chapter 2, Natural Resource Damage Assessment (NRDA) reports historically utilize habitat equivalency analysis (HEA) to account for wetland losses. HEA provides an analytical framework for estimating how much restoration is needed to compensate for the interim loss due to the spill. The objective of compensatory restoration is to deliver a fair level of compensation for the interim loss of the resource, meaning the value of the increase in the identified resources from the replacement projects should be equivalent to the value of the resources lost due to the injury. Thus, using HEA, the NRDA Trustees (see Chapter 2 for additional details on NRDA and Trustees) select restoration projects that are comparable in type and quality to replace the lost or damaged habitats.

To perform HEA calculations, Trustees must determine how long the injury will persist, the relative service level of the injured and replacement resources, and the lifetime of the replacement project. With this information, the Trustees can calculate the amount of the restoration

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

needed by establishing an equivalency between the quantity, usually measured by acreage, of lost or damaged habitat (and its associated services) and that generated through the compensatory restoration project over time. As noted in earlier discussions (NRC, 2011), HEA can fall short in identifying and valuing the habitat that connect to the public’s use of or benefits from the various ecosystem services provided by the wetlands.

Table 5.5 summarizes the state of the present NRDA practice to value the reduction of wetlands due to a spill as well as the metrics necessary to determine a value under the ecosystem services approach.

Because of the complexity of and challenges in the GoM ecosystem, including subsidence, sea level rise, and human activities, the HEA approach may not always offer the full range of restoration options. In contrast, the ecosystem services approach may offer a broader range of options to restore ecosystem services and enhance wetland resilience. As depicted in Table 5.5, application of the ecosystem services approach in the GoM is fairly simple from a concep-

TABLE 5.5 Provision and Valuation for Wetland Storm Mitigation

NRDA Practices

Resource Wetlands (salt marsh)
Typical approach to assessment Determine exposure pathways and spatial extent of vegetation oiled; collect and document any dead and oiled wildlife

Valuation Under the Ecosystem Services Approach

 
Ecosystem Service Hazard Moderation
Type of data needed for ecological production function

A. Plant type (or species), height, and density.

B. Percentage of area likely to experience acute toxicity and die-off.

C. Cross-shore and along-shore extent of wetland harmed.

D. Estimates of ability of the wetland to reestablish with or without human intervention.

 
Ecological production function Relationship between plant type, height, density and areal extent of vegetation and reduction of wave energy and storm surge.
 
Type of data needed for valuation

A. Location of structures, infrastructure, agriculture, etc., near the coast.

B. Value of structures, infrastructure.

C. Areal extent of marsh and biophysical condition.

 
Valuation method Avoided cost; calculate the expected damages associated with stormsurge. The value of the ecosystem service is equal to the reduction in expected damages.
 
Type of data needed for valuation of ecosystem service

1. Data on (A), (C), and (D) from the ecological production functions. Data on wetland extent and amount oiled would be collected in a standard NRDA, but other data likely would not.

2. Building the functional relationships to translate from data on plant type, height, density, and extent to likely height of storm surge; may be done via empirical relationships or modeling.

3. Building the functional relationship that translates height of storm surge to expected damage.

 

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

tual standpoint. For the GoM, where the baseline is changing rapidly, the ecosystem services approach first estimates the wetland loss over the next few decades that would have been expected if the spill had not occurred. The baseline must be observed over several decades in order to derive a relatively stable valuation, because episodic events such as storms, which may have both positive and negative effects, and long-term trends affect the trajectory. Next, the approach calculates the expected wetland loss over the same time period with the spill effects considered. This estimate will have high uncertainty, which ideally should be considered, but it will not be considered here for the sake of simplicity.

Finding 5.4. An ecosystem services approach can develop production and valuation functions, which calculate a net present value of the incremental loss of wetlands and human-engineered structures due to storms. This approach allows for identification and comparison of alternative mitigation options to find the preferred restoration option, which may increase resilience more so than simply restoring the damaged wetland to its original state.

Opportunities for Restoration

Against a natural backdrop of significant continuing wetland loss due to a variety of circumstances, including subsidence, dredging of canals, salt intrusion, and sediment starvation, are a number of options for wetland restoration. These options include elevating existing wetlands to a range that restores the resilience of the wetland and increases its elevation capital, and creating and introducing genetically modified wetland plants or hybrids that produce massive quantities of roots and rhizomes that more efficiently trap mineral sediment.

The former can be accomplished more broadly by diverting sediment-laden water from the Mississippi River into degrading wetlands or, more locally, by creative uses of dredge spoil. For example, thin layer disposal of spoil, accomplished by spraying sediment slurry into adjacent marshes, is possible in the vicinity of dredging operations (Wilber, 1993).

With respect to bioengineering approaches, natural hybrids of Spartina exist, such as those found in San Francisco Bay, California (Ayres et al., 2004; Rosso et al., 2006), with superior capabilities to expand and trap sediment. The introduction of genetically modified plants, or even hybrids, would be controversial, but would be analogous to what has been developed and practiced in agriculture for many centuries.

To accelerate the degradation of oil residues in marsh sediments, the process of bioremediation can be used to exploit the activities of microbial communities to restore oil-polluted environments (see “Near-Shore and Onshore Biodegradation” discussion in Chapter 4). Bioremediation of petroleum pollutants often involves using the enzymatic capabilities of the indigenous hydrocarbon-degrading microbial populations and modifying environmental factors, particularly concentrations of electron acceptors (oxygen, nitrate), fixed forms of nitrogen, and phosphate, to achieve enhanced rates of hydrocarbon biodegradation (Atlas, 1991; Swannell et al., 1996). It has been demonstrated experimentally that degradation of oil can be enhanced by the addition of the inorganic nutrients nitrogen and phosphorus (Röling et al., 2002). Degrada-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

tion of oil can also be enhanced by the dispersion and emulsification of oil in aquatic systems and by absorption by soil particulates in terrestrial ecosystems (Leahy and Cowell 1990), processes that happen naturally or, in the former case, with the aid of added dispersants. However, the application of dispersants in wetlands is generally prohibited without a case-by-case review and approval from the Environmental Protection Agency (EPA) and the U.S. Coast Guard in their capacities as cochairs of the Regional Response Teams (NRC, 2005a).

Fisheries

Introduction

The second case examines the fisheries in the GoM, particularly the provisioning ecosystem service of seafood and fish-based products. Fisheries clearly offer an important cultural ecosystem service through recreational fishing, which will be considered only briefly here. Like for wetlands, substantial baseline data for fisheries exist, and significant efforts have been made to develop ecological production functions through various fisheries models (see Chapter 2). The values of both the provisioning and cultural services offered by fisheries are measurable by traditional economic methods (Eide, 2009). Given their economic importance, fisheries have been the focus of numerous policies (Feral, 2009) and management plans (Die, 2009) aimed at maintaining the flow of their services to provide the greatest benefit possible to society. The importance of understanding and managing marine ecosystems to ensure sustainable provision of the ecosystem services provided by fishing is now enshrined in state laws such as California’s Marine Life Protection Act,1 federal laws such as the Magnuson-Stevens Fishery Conservation and Management Act (“Magnuson-Stevens Act”),2 which governs most of the major fisheries in U.S. waters of the GoM, and international treaties that call for an ecosystem services approach to the management of marine fishery resources (Garcia and Cochrane, 2009; Garcia et al., 2003). At both the national and international levels, it has been recognized that fishery management decisions should be based on the best available scientific information (Magnuson-Stevens Act, 16 U.S.C. §1851(2); FAO, 1995).

Provisioning Service

Food and Fish-Based Products In 2011, the GoM produced more than 200 million pounds of shrimp valued at $352 million, which accounts for nearly 68 percent of U.S. landings. The GoM also produced 18 million pounds of oyster meat valued at $84 million, accounting for 64 percent of U.S. landings. Although not used for food, menhaden landings were another regional top earner, with 1.6 billion pounds (66 percent of U.S. landings) earning $110 million (NMFS, 2012). Sport fishing is also a major economic engine. In 2011, an average of 23 million fishing

_________________

1 Cal. Fish & Game Code § § 2850–2863.

2 16 U.S.C. §1801 et seq.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

trips took place in the Gulf States (NOAA, 2013a), generating sales of $9.9 billion and income of $5.1 billion.

Seafood harvesting and recreational fishing take place in a variety of ecosystems within the GoM, from the coastal bays to the edge of the exclusive economic zone (NMFS, 2012). Seafood includes not only sessile organisms such as oysters, but also highly migratory species such as tunas. Many demersal organisms (associated with the bottom of the sea as adults), such as shrimp and some species of fish, often have pelagic larvae that connect populations over ocean basin scales (Cowen et al., 2006). As a result, a wide array of GoM fishery resources may have come in contact with substrates or waters polluted by the DWH oil spill or the spill responses.

Additional Ecosystem Services

Although fisheries aim to provide two main ecosystem services, provisioning (food) and cultural (recreation), fishing affects our ability to extract other services from the ecosystem. For example, fishing practices may cause changes to benthic communities (Wells et al., 2008) or remove fish predators (Ruttenberg et al., 2011), and thereby affect regulating and supporting services, or degrade reefs (Dulvy et al., 2004). The presence of such interactions between fishing and ecosystem services other than those related to seafood and recreation means that disruption of fishing activities caused by an oil spill will have consequences for other ecosystem services.

Quantifying Changes in Baselines

Recognition of the value of ecosystem services derived through fishing activities and of the need to base resource management decisions on science has meant that some of the monitoring and assessments required for understanding the provision of seafood have been in place for a number of decades (Beverton, 1998). Therefore, in comparison to other ecosystem services, those related to the provision of seafood, and to a lesser extent recreational fishing, have a long history of research, monitoring, and quantitative evaluation of the impacts of human activities (Hilborn, 2012).

Most of these research and monitoring efforts have focused on how to manage fishery productivity by controlling harvests or fishery inputs in a single fishery population context (Pope, 2009). Some researchers assert that fisheries management has failed (Jackson et al., 2001; Myers and Worm, 2003) because it has not followed a holistic ecosystem approach, while others suggest that this approach is the reason for management failures (Hilborn, 2004; Hilborn et al., 2004; Mace, 2004), while still others suggest that the problems are often more related to the failure of fishery institutions (Mesnil, 2012) and limitations of fishery laws (Dell’Apa et al., 2012). What is clear, however, is that much knowledge about marine ecosystem processes has been gained because fisheries have functioned as large-scale ecological experiments (Jensen et al., 2012).

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Unfortunately, the impacts on fishery productivity from coastal development (Mora et al., 2011), pollution from freshwater catchments (Caddy and Bakun, 1995), and dumping of debris (Ribic et al., 2012; Wei et al., 2012b) and contaminants (Brodie and Waterhouse, 2012), including oil spills (Barron, 2012; Garza-Gil et al., 2006; Penela-Arenaz et al., 2009), are not well understood. The impacts of ocean acidification (Kaplan et al., 2010) and global warming (Eide, 2008; Sherman and Adams, 2010) have only recently been studied.

Market-based baseline information collected by state and federal agencies routinely includes data on landings by weight, by dollar value at state, regional, and national scales, by species, and by distance from shore (NMFS, 2012). These data can provide some initial estimates of impacts from events such as hurricanes; for example, in Figure 5.6 the observed reduction in value for Louisiana’s landings in 2005–2006 may reflect the impact of Hurricane Katrina, which hit the northern GoM coast in August 2005 and destroyed a large part of the fishery infrastructure (Impact Assessment, Inc., 2007), while the reduction in value for 2010 may be attributed to the DWH oil spill.

Most fishery models describe the productivity of a fish population as a function of population dynamics (Quinn and Deriso, 1999). The amount of seafood that can be sustainably harvested is thought to be a function of historical catch rates, the natural mortality suffered by the population, and the population’s capacity to reproduce. The resulting balance between these processes is then reflected in the relationship between harvested fish and the abundance remaining in the population, most often measured indirectly through observation of standardized catch rates (Maunder and Punt, 2004). Ecological production functions for fish stocks can then be derived by modifying fishery models that consider economics (Sanchirico and Springborn, 2010).

Even for the best-studied and most valuable fish populations, such as bluefin tuna (Fromentin and Powers, 2005) or Gulf menhaden (Smith and Vaughan, 2011), estimates of fluctua-

image

FIGURE 5.6 Value of commercial landings of fish by the Gulf states. SOURCE: Data from NMFS 2002–2011. Fisheries: Ecological Production Functions and Valuation.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

tions in productivity cannot be precisely characterized (Figure 5.7). Long-lived species such as bluefin tuna have shown production cycles ranging from 20 to 100 years, which may be related to the dynamics of the tuna population or to changes in the ecosystem (Ravier and Fromentin, 2001). Because high uncertainty is present in the estimation of historical abundance, predicting future population trends for fish populations that are confined within the GoM (Walter and Porch, 2008); NOAA, 2011b,c,d,e) and those that migrate through it (ICCAT, 2010, 2011, 2012) is a difficult endeavor.

One of the most serious limitations with estimating stock size is that, for most species, current assessments of GoM fishery resources are not spatially explicit—that is, they only provide estimates of abundance for populations of large migratory fish that encompass the entire GoM or the entire Atlantic. Recently, Carruthers et al. (2011) estimated spatially explicit abundance for migratory fish; however, their model still does not resolve abundance at scales smaller than

image

FIGURE 5.7 Historical sustainability indices for some of the most important fish stocks in the Gulf of Mexico that may have been affected by the oil spill or by the fishing closures imposed after the oil spill. NOTES: Indices for (a) brown and white shrimp (Nance, 2009), (b) Gulf menhaden (NOAA, 2011c), (c) red grouper (SEDAR, 2010), and (d) western stock of Atlantic bluefin tuna (ICCAT, 2011) are provided in the four line graphs above. Indices at or above 1.0 indicate sustainable exploitation. All biomass indices are relative to overfishing reference points, either the biomass at maximum sustainable yield (B) or the minimum stock size threshold (MSST). Some of the common sources of uncertainty in estimates are highlighted: data and estimation uncertainty (red grouper and Atlantic bluefin tuna) and assessment model uncertainty (menhaden).

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

the entire GoM. This lack of resolution challenges assessment of the spill’s impact on these resources because the direct impact of the spill is most likely to be restricted in space to the areas closest to the oil.

Although population assessments do not estimate spatially explicit population abundance, there are indices of relative abundance for some species that have some measure of spatial resolution. Many of the indices of relative abundance for fish populations in the GoM use the National Marine Fisheries Service (NMFS) statistical areas as explanatory areal factors. These statistical areas (Figure 5.8) encompass vast areas of the GoM (Scott-Denton et al., 2011), and they may provide enough spatial resolution to test hypotheses about the impact of a large spill such as the DWH, but are clearly inadequate for smaller spills. More recent developments in fishery data collection, such as the introduction of vessel monitoring systems in the reef fish fishery of the GoM, can provide more precise geolocation data that could be used to obtain finer-scale indices (Saul, 2012).

image

FIGURE 5.8 Spatial scales for which fishery data are available in the Gulf of Mexico. NOTE: Each area of the ocean represents a statistical area used by NMFS in the analysis of fishery data. Areas represent the smallest scale at which representative and comprehensive historical data on catch and fishing effort are available. SOURCE: NMFS, 2010a.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Finding 5.5. Fisheries provide one of most important and lucrative provisioning services in the GoM via seafood production and cultural services via recreational fishing. Despite many longterm studies and ongoing development of fisheries models, the ability to detect spatial and temporal differences in fishery productivity of the GoM fish populations is often limited.

Given the difficulty in separating the effects of environmental forcing on ecosystems from those related to population processes, fishery management often assumes that the environment has no effect on productivity, or conversely that population productivity is stationary. By assuming that changes in productivity are related to harvest, managers can take the precaution of curtailing fishery removals. Kell and Fromentin (2007) have shown that it is possible to design robust management strategies despite the lack of knowledge about all of the factors that affect the productivity of species such as bluefin tuna. In theory, it should be possible to design and implement precautionary management measures that acknowledge the uncertainty of the impacts of the DWH oil spill on fishery resources and therefore ensure sustainable provision of seafood into the future. However, adopting such measures would likely meet some resistance from stakeholder communities that rely explicitly on harvesting of these resources for their livelihood and well-being, as has often been seen when fishery managers seek to implement precautionary management. In fact, the difficulties of implementing precautionary management may be even greater when its scope is at the ecosystem level rather than at the level of a specific species or fishery (Gerrodette et al., 2002).

Given the extensive data collected by various federal and state agencies (NOAA NMFS, Texas Parks and Wildlife Department, Florida Fish and Wildlife Conservation Commission, Louisiana Department of Wildlife and Fisheries, Alabama Department of Conservation and Natural Resources, Mississippi Department of Marine Resources, Gulf of Mexico Fisheries Management Council, and Gulf States Fisheries Commission) on commercial fishing activities and the dockside values of the fish, estimating the direct value of the fish and food provisioning service of commercial fisheries to fishermen is fairly straightforward: the dockside value of the fish (the amount that the fishermen receives) minus any expenses they incurred to capture those fish. What is less clear is the value as the commercially caught fish makes its way through the supply chain and finally to the consumer’s plate. Although the amount of commercially caught fish in the Gulf decreased in 2010 from the previous year (544 metric tons, down from 635 metric tons), potentially because of the extensive closures associated with the DWH oil spill, in 2011 the total catch increased to 862 metric tons, for a value of $797 million (Figure 5.9) (NMFS, 2012).

Commercial fishing values are captured through established mechanisms, but there is no similar mechanism to capture the value of subsistence fishing, which is an extremely important activity for many people along the northern Gulf Coast (see Box 2.2 in Chapter 2). An effective measurement of the food provisioning service would include not only commercial fishing, but also subsistence fishing.

The methodology for evaluating the economic effects of an oil spill, like any other effect of pollution, is relatively simple in concept (Lipton and Strand, 1997). In commercial fisheries, the costs of economic pollution are derived from either reduced production (due to die-offs

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

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FIGURE 5.9 Gulf of Mexico commercial fishery landings by weight (thousands of metric tons) and value (millions of $) for 1950–2011. SOURCE: NMFS, 2012.

or fishery closures) or by a drop in consumer demand due to the perception of reduced fish quality or safety (Lipton and Strand, 1997). However, the application of such methods provides few insights into the ecosystem’s functioning. Attempts at making long-term predictions of fish abundance with traditional fishery management models have been relatively unsuccessful, making it difficult to believe that we can do better with long-term predictions of impacts of the oil spill. Furthermore, predicting indirect impacts, such as those mediated through the food chain, will be even more challenging. Recent advances in the development of more comprehensive ecosystem models provide some hope; however, these methods can, so far, only provide deterministic predictions (Field and Francis, 2006; Kaplan and Leonard, 2012).

DWH Spill Impact on Fisheries

As already discussed in this report, the impacts of the DWH oil spill can be far-ranging and long-lasting. However, only a few studies have started to present evidence of these impacts. In this section we discuss two categories of impacts: those that directly affect animal or plant fitness and those that affect fishers or consumers of seafood.

The most direct impact of oil on living organisms relates to the toxicity of oil compounds. Only a few studies have so far provided quantitative data on the toxicity of the DWH oil spill on fish. Analysis of a data set consisting of 853 trawl samples taken between 2006 and 2010 did not show any loss in seagrass-associated juvenile fish abundances after the DWH oil spill

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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(Fodrie and Heck, 2011). In fact, for more than half of 20 commonly collected species, the catch rate was significantly higher in 2010 (α = 0.05), which the researchers suggest might have occurred as a result of the fishery closures (see below). Catch-per-unit-effort of the most abundant species, pinfish (Lagodon rhomboides), was higher in 2010 (Fodrie and Heck, 2011). Post-spill community-level shifts in seagrass-associated fish assemblages were not observed.

Nonnative zebrafish, Danio rerio, were used in models of responses of embryonic developmental to exposure to water-accommodated fractions of DWH MC-252 crude oil to assess their potential to induce toxic effects (de Soysa et al., 2012). Results indicated that the oil was capable of causing significant defects in embryogenesis, resulting in cell death (apoptosis) and abnormalities in locomotor behavior, sensory and motor axon pathfinding, somitogenesis, and muscle growth. In addition, heavily weathered oil from the DWH oil spill has also been implicated in reproductive impairment and aberrant protein expression in gill tissues (physiological impairment) of larval and adult Gulf killifish (Fundulus grandis) that are common to Louisiana and Alabama coastal marshes (Whitehead et al., 2011). Such effects on fish reproduction are consistent with previous reports of direct effects of benzo[a]pyrene on the reproduction of fathead minnows (Pimephales promelas) (White et al., 1999). Despite the fact that only trace hydrocarbon concentrations were detected in the water column, effects characteristic of polycyclic aromatic hydrocarbon (PAH) exposure were apparent for up to 2 months after the initial exposure at Grande Terre, Louisiana, where oil came ashore (Whitehead et al., 2011).

Indirect effects of the toxicity of oil compounds include those related to the populationlevel and ecosystem-level responses to fitness change. Whenever the fitness of a given life history stage, such as juvenile fish, is affected by oil toxicity, we may expect population-level responses in subsequent life history stages even if they are free from the direct effects of exposure to oil. This is especially relevant for fish larvae and juveniles that inhabit the coastal areas and the surface of the open ocean, where concentration of oil is often the greatest after a spill. Such indirect effects on fish populations may take years to reveal themselves for long-lived species and thus affect seafood provision for decades.

Some measure of the potential disruption to the provision of seafood caused by the spill can be visualized by examining the spatial extent of the fishery closures (Figure 5.10) imposed by NOAA in its aftermath. These closures were intended to limit the risk of harvested seafood (generally adult fish and shellfish) from reaching the human consumer, not to protect the organisms from the effects of oil (NOAA, 2010). The fishery closures alone may have decreased fishery landings in the GoM by as much as 20 percent by preventing fishermen from accessing resources (McCrea-Strub et al., 2011).

The closures, however, underestimate the spatial extent of the possible indirect impacts of the spill on fishery resources because some fish can migrate through the spill area without being caught (Galuardi et al., 2010) and larvae present in the spill area may survive and end up recruiting as juvenile fish elsewhere in the GoM or other areas of the Atlantic (Muhling et al., 2012).

According to news reports and presentations to the committee by local GoM community spokespeople, a lack of demand caused seafood sales to drop after the spill (McGill, 2011). A study commissioned by the Louisiana Seafood Promotion Board and conducted by the market

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

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FIGURE 5.10 Fishery closures imposed by NOAA to ensure seafood safety, effective May 17, 2010. The closed areas changed daily as NOAA sampled seafood in the area and the geographical extent of the detected oil changed. SOURCE: NOAA.

research company, MRops, found that greater than 70 percent of survey participants expressed some degree of concern regarding the safety of GoM seafood after the spill. The study also found that 23 percent of participants claimed to have reduced their seafood consumption after the spill. These results, which demonstrate the potential impacts on the GoM seafood market, have been cited frequently in the media and other reports (McGill, 2011; Upton, 2011).

Finding 5.6. Fishery closures in response to the DWH oil spill serve as one limited measure of the impacts to fisheries. Another impact of the spill and the subsequent closures was the public’s concern about the safety of seafood from the GoM, despite efforts by federal and state governments to establish a comprehensive protocol to ensure the safety of GoM seafood. The DWH oil spill may result in longer-term consequences to seafood production beyond those caused by the cessation of harvest from oil spill–related fishing closures, including impacts to productivity or fitness, which may take years or decades to determine.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Further, any mortality or reduction in individual fitness caused by the spill directly or indirectly through trophic interactions may determine the productivity of fishery resources into the future. Potential changes in productivity due to an oil spill, and the corresponding consequences to fishery harvest, may take years or, for some species, decades to transfer through the ecosystem, as shown by the time taken for fishing effects to cascade through marine food chains (Carscadden et al., 2001; Estes et al., 2009; Salomon et al., 2010; Sommer, 2008).

Trophic cascades may result from the indirect impacts of pollution (Jackson et al., 1989; Sala et al., 1998). The ripple effects of such disturbances on an ecosystem can last a long time (Peterson et al., 2003) and may ultimately lead to persistent changes in the ecosystem structure and its functioning. Fish can show detectable levels of contaminants long after a spill (Jewett et al., 2002), and sublethal impacts of these contaminants may be more significant than previously suspected (Peterson et al., 2003).

Prior to the DWH oil spill, oil spills have typically been local events that affect mostly the vicinity of the incident where oil was released. Therefore, impacts of oil spills have a strong spatial signal, with effects being stronger on ecosystem components that are closest to the spill site (Roth et al., 2009) and weaker on those that are more distant (Bustamante et al., 2010; Diez et al., 2009). A recently completed survey (Murawski et al., in preparation) of approximately 7,500 offshore fish in 2011 and 2012 reveals a similar signal pattern in the frequency of abnormal skin lesions coupled with elevated PAH levels found in bile of fish caught in the northern GoM. Fortunately, the frequency of lesions dropped significantly by 2012, indicating that the exposure was more episodic than chronic in nature. PAH concentrations are typically indicative of oil-related pollution, and the composition of the PAH compounds in red snapper was similar to those found in fish collected near the DWH wellhead. It is prudent to acknowledge that most fish can metabolize PAHs, and liver and muscle tissue samples in these fish had PAH levels falling well below the Food and Drug Administration’s “levels of concern” (Murawski et al., in preparation).

Natural Resource Damage Assessment

As discussed in previous sections of this report, understanding of fisheries is dominated by the economic valuation metrics of the commercial and recreational fish stocks that many of the state and federal resource management agencies have been collecting for many years. These data, coupled with the estimates of stock size and recruitment (which carry varying degrees of uncertainty and predictability), represent some of the metrics used in the traditional NRDA process (see Table 5.6). By contrast, the ecosystem services approach to valuation allows for a more comprehensive integration of environmental variables, such as the condition of relevant habitats, that influence the condition of fisheries. This integration can also include the impacts of fishing on other ecosystem services, so that, in the case of a fisheries closure, for example, changes (including positive changes such as reduced fishing pressure and subsequent cascades for the food web) can also be identified.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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TABLE 5.6 Provision and Valuation for Seafood Provision

NRDA Practices

Resource Commercial Fisheries
Typical approach to assessment

1. Measures of fishery landings.

2. Measures of fishery stock and recruitment.

3. Estimates of losses due to environmental injury/toxic effects.

Valuation Under the Ecosystem Services Approach

Ecosystem service Food and Fish-Based Products (commercial and subsistence)
Type of data needed for ecological production function

A. Measures of fishery landings.

B. Measures of fishery stock and recruitment.

C. Indices of environmental parameters affecting recruitment of harvested species.

D. Indicators of harvest pressure (catch, fishing effort).

Ecological production function

1. Relationship between ecosystem and habitat conditions and fishery productivity.

Type of data needed for valuation

1. Market price of commercial fish.

2. Fishing cost per unit effort (capital, labor, fuel).

3. Subsistence fishing activity level and species caught.

Valuation method Market valuation: Calculate profit from fishing. Use market price and harvest data to calculate revenue. Use cost data along with revenue calculation to calculate profit. Calculate the value of subsistence-caught species based on the market equivalent price.
Type of data needed for valuation of ecosystem service

1. Data on industry costs, dockside prices, and catch from subsistence fishermen.

2. Building the functional relationship between ecosystem and habitat condition and fishery productivity. This may be done via empirical relationships and/or modeling.

 

Finding 5.7. Relative to the NRDA process, valuation efforts utilizing the ecosystem services approach can integrate more of the environmental variables that influence the productivity and recruitment of the fisheries, particularly the condition of the habitat that could be directly affected by an event such as the DWH oil spill.

Opportunities for Restoration

The ability to manage possible impacts on the provision of seafood and fish-based products as an ecosystem service also relies on our knowledge of the natural resilience of marine ecosystems. As discussed in Chapter 3, resilience is measured by the rate and extent to which recovery can happen after disturbances, such as an oil spill. Harwell and Gentile (2006) report that it took less than 20 years for Prince William Sound to recover from the Exxon Valdez oil spill,

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

and Deriso et al. (2008) partially confirm their conclusion when they dismiss the argument that the Exxon Valdez oil spill led to the local collapse of Pacific herring.

Other researchers, however, dispute such assessments (Matkin et al., 2008; Peterson et al., 2003). Furthermore, in marine ecosystems, internal feedback mechanisms can promote the persistence of disturbances. For example, it seems that adult herring, “released” from predator control because of the depletion of cod from overfishing, can prevent the rebuilding of cod after the cessation of overfishing by consuming the early life stages of cod (Bakun and Weeks, 2006). Examples such as this are reminders that marine ecosystems can behave counterintuitively to what is observed in terrestrial systems and have routinely frustrated fishery rebuilding efforts by modelers and managers alike.

In the GoM, restoration efforts are likely to be widespread as resources become available from the responsible parties, but if early efforts are indicative, then coastal habitats including wetlands and oyster and seagrass beds are likely targets of restoration. This is, in large part, because habitat restoration can simultaneously enhance multiple ecosystem services.

Direct evidence of effects of habitat restoration on marine fisheries productivity is mostly limited to the effects observed from restoration of oyster reefs (Kim et al., 2012; Nestlerode et al., 2008). However, a recent analysis of habitat restoration efforts for Columbia River salmon identifies major errors in the conceptual foundation of many aquatic habitat restoration efforts (Williams, 2006). It is therefore essential that habitat restoration efforts are documented with a proper and standard set of habitat project-level metrics so that decision makers have the information they need to decide whether projects are likely to mitigate the effects of the DWH oil spill on fisheries (Barnas and Katz, 2010).

Finding 5.8. Aside from application of precautionary catch limits to mitigate the potential impacts of the DWH oil spill on fisheries, habitat restoration, because of its potential to enhance a suite of ecosystem services, may prove to be one of the more effective ways to restore fishery productivity in the GoM. It is also essential that habitat restoration efforts are documented with a proper and standard set of habitat project-level metrics so that decision makers have the information they need to decide whether projects are likely to mitigate the effects of the DWH oil spill on fisheries.

Marine Mammals

Introduction

The third case study focuses on marine mammals in the GoM, particularly bottlenose dolphins. From February 28, 2010, to December 9, 2012, a period of approximately 33 months, at least 817 dolphins were found on the shores and in the marshes of the northern GoM; all but 5 percent were dead. As a rough comparison, the number of dolphins stranded in that region between 2002 and 2009 was approximately 100 per year.3 Because some unknown portion of

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3 See running tally at http://www.nmfs.noaa.gov/pr/health/mmume/cetacean_gulfofmexico2010.htm.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

dead dolphins are neither found nor reported, these figures underestimate actual mortality (Williams et al., 2011). NMFS has officially designated an “unusual mortality event” (UME) in the northern GoM based on the unexpectedly high levels of bottlenose dolphin mortality along the coast.4 Such a designation calls for intensive data and sample collection and a rigorous, coordinated study into the cause. Investigation of the mortality event has been subsumed into the NRDA process related to the DWH oil spill. Because it is not yet known if this aspect of the NRDA process will be litigated among the various parties, scientific findings from the investigation of the mortality event have not been made public.

The uncertainty surrounding the UME invites an examination of the range and extent of ecosystem services that would be altered, diminished, or lost if dolphins were affected by the spill. The exercise also has application for other marine mammals that could have been affected by the spill. Although applicable to marine mammals in general, this case study focuses on the scientific and educational, aesthetic, spiritual, and recreational benefits derived from dolphins in the GoM ecosystem.

Cultural Services

Scientific and Educational Because of their proximity to the shoreline, certain populations of bottlenose dolphins that reside in GoM coastal waters, bays, and sounds are ideal subjects for observational studies from the beach or small watercraft. This research provides invaluable scientific information on dolphin populations, and much of what we know about their natural history was derived from such observations. A single day-long vessel excursion can yield a wealth of data—for example, size, age, and composition of the group, social structure and dynamics, feeding behavior, and mother-calf interactions. Gathering the same kind of data on a pelagic species is difficult, costly, and can take decades. Capture-and-release studies on coastal dolphins have become the only safe and reliable way to examine live specimens, from snout to flukes, and to obtain repetitive blood and other samples to determine the health status of the animals and, over time, their population (Wells, 2009).

These studies also provide an opportunity to broaden our understanding of the links among the health of these animals, the quality of their environment, and the potential impact of human activities on their well-being. For example, bottlenose dolphins along the GoM coast from Florida to Texas are commonly exposed to toxins produced by certain harmful algal blooms (HABs), and growing evidence implicates such exposure with dolphin stranding events (Fire and Van Dolah, 2012). Worldwide, HABs are spreading geographically and increasing in frequency for reasons that appear to include nutrient inputs from land sources (Olascoaga et al., 2007). Another issue is that dolphins are continually exposed to infectious agents, such as morbilliviruses (Duignan et al., 1996), and a wide variety of potentially harmful microbes, such as Brucella spp., that affect their reproductive and other internal systems, and plausibly affect their productivity (NOAA, 2011f). Dolphins in coastal waters are further exposed to potentially toxic chemical compounds, such as tributyltin (Kannan et al., 1996) and polychlorinated biphe-

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4 Note that the UME was declared more than 5 weeks before the DWH oil spill began.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

nyls (Houde et al., 2006), which accumulate in fat and other tissues and have the potential to reduce their immunological capacity to fight disease (Lahvis et al., 1995).

Finding 5.9. As with many other species and ecosystems in the GoM, dolphins are often subject to multiple stressors that are linked to environmental conditions and human activities.

Bottlenose dolphins in experimental settings can detect oil films on the surface, day and night, using vision and to some extent echolocation (Geraci et al., 1983). A dolphin’s contact with oil elicits a “startle” response normally associated with stress or annoyance and, given a choice, thereafter avoidance (Smith et al., 1983; St. Aubin et al., 1985). These studies suggest that dolphins found amidst oil may have overriding reasons to be there, like feeding, social cohesion, reproduction, or simply migration through the spill area. Exposure to fresh volatile oil carries the danger of acute, possibly fatal, toxicity (Geraci, 1990). And while mere contact with older oil and sheens is not necessarily harmful to dolphins (Geraci, 1990), such environments may exert pressure on their social order, abundance, and quality of suitable prey, or other features of their life history that are less tolerant of change (Wursig, 1990). The net effect would plausibly add more stress to animals already exposed to contaminants, biotoxins, pathogens, and other stressors that combine to threaten the health of individuals and the vitality of populations. Dependent calves would be of particular concern. Studies under the NRDA process may shed light on whether the DWH oil spill has affected the health of dolphins in the GoM and any links between the spill and the mortality event.

Information gathered through these studies, together with fundamental physical, chemical, and biological descriptions of their habitat, is needed to identify the ecological production functions for coastal dolphin populations. As noted in Chapter 2, the cumulative information, in turn, forms the basis for valuing the ecosystem services that GoM dolphins provide. It is a long, multifaceted process that may be somewhat streamlined because dolphins are such desirable subjects to study.

Existence and Spiritual Services

In the United States, all marine mammals, including the bottlenose dolphin, have special standing. Completely protected under the Marine Mammal Protection Act of 1972, they cannot be harvested for sport or food except in limited circumstances (e.g., Native American subsistence hunting). Therefore, most of the public’s association with these species is through knowledge of their existence. Whether it be for their large brains, social behavior (nursing calves, tending their ill), apparent “smile,” large eyes, or wide media exposure, dolphins resonate with humans in ways that transcend biology, appearance, or place in the ecosystem. From early history, dolphins have been featured in Greek mythology, as religious symbols, and as icons in art and architecture. Today dolphins are bulwarks for advancing conservation policy regionally and globally. The United States invests significant public resources, including millions of appropriated dollars, into programs designed to protect marine mammal health and well-being,

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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as well as to assure that our use of ocean resources is compatible with the marine mammals’ long-term welfare. Much of this attention is tied to conserving a natural resource and the greater ecological good that it confers. Still, dolphins stand out among many species that profit by such protection.

On a personal scale, many people simply want to know that dolphins exist. The passion of that commitment can be seen during any stranding event, where volunteers show up by the hundreds in challenging, often harsh weather to lift an animal back to sea and watch it swim away. These types of events illustrate the high personal value that individual humans place on these animals and highlight how dolphins help humans to realize a sense of well-being (see Figure 2.1 in Chapter 2).

Recreation

Dolphin ecotourism is a growing industry nationally and globally. Apart from the financial benefits to operators and communities, dolphin-watching tours offer patrons unique noncontact recreational and educational opportunities. All five GoM states have tour operators specializing in dolphin watching. Expenditures that individuals make for these experiences provide some measure of their minimum value.

Revenues from these operations are uncertain, but relevant information is available from other parts of the country and could be used to help model/extrapolate values for this GoM ecosystem service. Direct annual revenues attributable to whale watching in Hawaii in 1999 were $11 million to $16 million (Utech, 2000) and roughly $21 million in New England. Globally, the whale- and dolphin-watching industry in 2008 generated revenues of $2.1 billion and is growing at a rate close to 4 percent per year (O’Connor et al., 2009). Beyond the economic value to the host communities, a case can be made that activities of this kind increase public awareness of the animals, invite dialogue on larger issues of the ocean environment, and are a natural platform for conservation education.

Supporting and Regulating Services

Bottlenose dolphins are apex predators in the food web of the GoM and thereby affect the flow of energy and nutrients throughout an ecosystem. What would be the consequences to that ecosystem if a dolphin population was gradually or suddenly reduced or eliminated? Would other large predators, like sharks, fill the vacated apex niche? Would there be increased productivity among their prey species, including commercially important species? Lessons from other dynamic natural systems help to illustrate the difficulty of forecasting the cascade of consequences that such a change might initiate and to highlight the importance of understanding complex trophic links.

Top predators, such as sharks and groupers, are required for a healthy coral reef, and their removal dramatically reduces coral growth and biomass because it leaves coral grazers unchecked (Friedlander and DeMartini, 2002). The decimation of apex shark populations from

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

northwest Atlantic ecosystems is enabling their former prey populations, including smaller sharks, skates, and rays, to expand unabated, similar to the herring-cod feedback loop discussed earlier in the fisheries case study. No longer regulated by shark predation, the cownose ray, Rhinoptera bonasus, has contributed to the collapse of local scallop fisheries (Myers et al., 2007). The digging activity of the rays also destroys eelgrass (Zostera marina), which otherwise provides habitat for communities with high faunal diversity and density. Removal of the eelgrass leaves unstable, less vital sand habitat (Orth, 1975), demonstrating that trophic cascades of this kind can have significant and long-term consequences. This example of the increase in the cownose ray, coupled with the decline of the local scallop harvest, lends itself to further analysis through the ecosystem services approach. Scallops are valued by humans as food (a provisioning ecosystem service), and the decline in the harvest can be quantified and results translated into a financial metric that would be readily understood by the public and by policymakers.

Finding 5.10. Bottlenose dolphins have a unique role in the GoM as both an apex predator and a charismatic species. Researchers have consequently studied this species extensively for decades, which allows for exploration of their role in providing a number of ecosystem services.

Changing Baselines

Estimating changes in the ecosystem services provided by dolphins will ultimately require an understanding of the underlying ecological production functions for dolphins and of the impacts of the DWH oil spill on the population dynamics of GoM dolphins. Determination of the causes of the strandings will be an important piece of the puzzle, because they may provide a link between the spill and mortality or loss of fitness for individual dolphins. The ability to relate the fitness loss to the status of GoM dolphin populations will depend on our knowledge of the size of these populations and the processes that may affect their dynamics. Evaluating the long-term effects of the spill will be especially difficult, requiring diligence and substantial commitment on the part of all parties involved.

In the Eastern Pacific, decades of research have yet to determine unequivocally whether certain dolphin populations have failed to recover because of persistent negative effects of a well-known stressor, tuna fishing, or because of yet-to-be-identified changes in ecosystem productivity (Gerrodette and Forcada, 2005; Reilly et al., 2005). The reason for these competing hypotheses relates, in part, to the simplistic assumptions made when trying to explain historical changes in marine mammal abundance (Gerrodette and Forcada, 2005) and in part to the difficulty of obtaining estimates of abundance that are precise enough to detect changes in population size of only a few percent per year, the maximum rates expected for long-lived mammals such as dolphins (Reilly et al., 2005). It is also possible that multiple stressors can be affecting the dynamics of these populations (Gerrodette and Forcada, 2005). The DWH oil spill highlights the critical need for long-term studies into population estimates and how they may correlate with conditions at all trophic levels, the roles of natural and human-induced factors

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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underlying health and disease, and the influence of climate change. This kind of information is needed to inform any discussion of the resilience of GoM dolphin populations.

Finding 5.11. Substantial uncertainty regarding the abundance of GoM dolphins and of the range of stressors that affect them will complicate the assessment of the true impact of the DWH oil spill on their populations and on the ecosystem services that they provide.

The challenge is further complicated by the stock structure of bottlenose dolphins in the GoM. The NMFS recognizes six major stocks: (1) northern bay, sound, and estuarine; (2) eastern coastal; (3) northern coastal; (4) western coastal; (5) northern continental shelf; and (6) northern oceanic. Given the distribution of these stocks and that of the spilled DWH oil, it is possible that all suffered some impacts from the spill. If so, the northern bay, sound, and estuarine stocks, northern coastal stock, and the northern continental shelf stock likely were the most affected. Prior to the DWH oil spill, the bay, sound, and estuarine dolphin stocks were the least understood with regard to life history information (Merrick et al., 2004).

DWH Oil Spill Impacts on Bottlenose Dolphins

Scientific findings from the dolphins associated with the UME are currently withheld from public review by the NRDA process. However, the scale of the event and timing of the spill demand attention. Because dolphins are an essential part of the GoM biotic community, it is logical to hypothesize that altering any component of that community, particularly with something on the scale of the spill, could affect dolphins at some point in their life history. Such effects may not be immediately obvious because (1) the animals adapt quickly with no observable population-level effects; (2) current research methods and technology are not sufficient to detect or measure certain types of changes that may occur; or (3) the primary insult becomes masked by complicating factors such as contaminants, pathogens, algal toxins, and the pressures of a degraded environment. Any effects of oil, whether by contact, ingestion through prey, or the extensive disturbances associated with containment and cleanup activities, would have to be considered in the context of other stressors the animals already face and would ultimately be expressed in ways that are subtle or removed in time, making it difficult to explicitly link health insults or mortality with the spill. Is it possible the future will reveal some unforeseeable connections as remote in time and space as post-war whaling and damaged kelp forest communities? Once a disturbance starts, cascades can progress for years, decades, or longer, affect multiple trophic levels, and lead to ecological shifts that would not have been predicted (Gerrodette and Forcada, 2005). We should be alert to all factors, natural or otherwise, that place even local dolphin populations at risk, and, when analyzing plausible causes of mortality events, we should take a deep look back in time.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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Cultural Services: Ecological Production Functions and Valuation

As mentioned previously, dolphins provide services that are based in recreation and tourism, as well as aesthetics and spiritual well-being for many humans. The value for recreation and tourism can be assessed in market terms. One method for doing so is the travel cost method. As described in a National Research Council report (NRC, 2011, p. 105),

travel cost studies use information on trips that individuals make to recreational sites and the expenditures of time and money involved in making the trip” (Freeman, 2003). Travel cost studies typically use “random utility models” in which the value (utility) of a visit to a given recreational site is a function of distance from sites, site access fees, observable site characteristics (environmental quality, site facilities, etc.), observable characteristics of individuals (income, education, etc.), as well as unobservable characteristics of individuals (idiosyncratic preferences). Travel cost methods allow an analyst to trace out a demand function for site visits by varying the implicit price of a visit (travel cost plus access fees) faced by individuals and observing the number of trips taken.”

Further, by looking at sites of varying environmental quality, the value of improved environmental quality can be estimated or the damage to a site can be quantified. If damage to dolphins occurs and there are fewer dolphins to view, then presumably there will be fewer visitations and therefore lower expenditures. Linking of the changes in dolphin populations to changes in visitations to dolphin-viewing destinations would be required for an effective assessment of the impact on recreational values from this specific activity.

An additional method to estimate the value of services provided by dolphins is passiveuse valuation, which is often used when considering spiritual and aesthetic services. Carson et al. (2003) conducted one of the most extensive studies to measure the impact of an oil spill on passive-use values, with regard to the Exxon Valdez oil spill of 1989. They assessed the spill’s impact on murres and bald eagles rather than marine mammals, but their results demonstrated a significant willingness-to-pay to avoid similar damages in the future of $4.87 billion in passive-use values. A subsequent study (Loureiro et al., 2009) after the Prestige oil spill in Spain, which built upon the valuation work conducted on the Exxon Valdez spill, estimated passiveuse losses with respect to marine birds and mammals and produced similar results. Summing from the household level, total willingness-to-pay was approximately $750 million, a rather substantial amount.

Certain regulations (e.g., under the National Environmental Policy Act of 1969) may require evaluation of passive-use values before any assessments of the dolphins’ value are undertaken. In many cases, federal agencies have neither the time nor the resources to conduct original valuation studies, and, in such cases, benefit transfer approaches might be practical. Loomis (2006) demonstrated that a complete quantification of value must include not only the costs of an action, but also the benefits. He identified and monetized several important benefits of sea otters along the California coast that were missing from the draft supplemental environmental impact statement prepared by the U.S. Fish and Wildlife Service on sea otter range expansion (Loomis, 2006). The passive-use/existence values were significantly greater than the direct-use

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

values. Similarly, a national estimation of the willingness-to-pay for expanded protection of the Steller sea lion in Alaska yielded a benefit of at least $5.8 billion annually (Giraud et al., 2002), demonstrating a strongly positive existence value for a protected species.

A recent effort to assess the economic value associated with recovery of marine mammal populations in Canada (Boxall et al., 2012) cites the need to establish marine protected areas to ensure recovery of the valued species. The results indicate that average willingness-to-pay per household ranges from $77 to $229 annually. As a nation, Canada would be willing to support recovery programs that improve the current at-risk status of the beluga whale and harbor seal at a level of $962 million–$2,850 million per year. These results are particularly relevant to the recovery efforts linked to the DWH oil spill. If the NRDA process determines that GoM bottlenose dolphins have been significantly impacted, then a part of the required restoration may involve protecting habitats that are important to them. Having an understanding of their value to the public provides a valuable context for any type of tradeoff analysis.

Natural Resource Damage Assessment

The Interim Report (NRC, 2011) and Chapter 2 of this report discussed the habitat and resource equivalency approaches (HEA and REA) to NRDA that are commonly used by the Trustees to assess injuries and services lost because of damages to habitats and wildlife. With respect to marine mammals, and in particular, the bottlenose dolphin, REA is likely to be one of the methods used by the Trustees for the DWH oil spill. Table 5.7 describes the kinds of data that would likely be collected by the Trustees for such an analysis, as well as the data needed to incorporate an ecosystem services approach into the existing NRDA framework. Data limitations may impede the ability to fully develop ecological production functions for dolphins, in contrast to the wetlands and fisheries. Nevertheless, the approaches outlined in the Interim Report (NRC, 2011) can provide a useful framework for the Trustees and other decision makers who are undertaking an ecosystem services approach to evaluate the impacts to marine mammals, while maintaining concordance with the ongoing NRDA process.

Opportunities for Restoration

Under the current Marine Mammal Protection Act in the United States, there are no specific restoration plans in place for bottlenose dolphins. If the NRDA findings establish a linkage between the recent mortality event of dolphins in the GoM and the DWH oil spill, then a major opportunity will exist to establish a plan to protect and restore dolphin habitat and to reduce mortality caused by human activities, such as bycatch from fishing. Strategies to reduce dolphin bycatch have already been implemented in the Bottlenose Dolphin Take Reduction Plan (BDTRP) for neighboring Eastern Atlantic bottlenose dolphin populations (NOAA, 2012c). A similar plan could be developed, if necessary, for the GoM.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

TABLE 5.7 Provision and Valuation for Marine Mammals—Recreation

NRDA Practices

Resource Marine Mammals (dolphins)
Typical approach to assessment Determine exposure pathway: Collect and document any dead or sick dolphins. Quantify the numbers dead or dying and, where needed, apply models from similar cases to estimate/extrapolate the number of dead or dying that were not directly observable.

Valuation Under the Ecosystem Services Approach

Ecosystem Service Recreation
Type of data needed for ecological production function

1. Numbers of marine mammal–watching operations and visitation rate.

2. Measures of dolphin standing stocks, reproduction, and recruitment to near-shore GoM.

3. Estimates of the ability of populations to recover (resilience) with and without human intervention.

 
Ecological production function Relationship between dolphin condition and quality of water and food sources. Understanding of the direct impact from exposure to oil, as well as response actions taken to alleviate the spread of the (surface/substrate) plume.
 
Type of data needed for valuation Survey information on commercial marine mammal–watching trips in the GoM.
 
Valuation method Travel cost. Use information on recreation trips, time and resource costs of trips to calculate willingness-to-pay for recreational mammal–watching trips.
 
Type of data needed for valuation of ecosystem service

1. Collecting data on (2) and (3) from above.

2. Building the functional relationship between water quality, food or prey quality, and dolphin condition; may be done via empirical relationships or modeling.

3. Estimation of value using travel cost (random utility model).

 

Finding 5.12. If a determination is made that the recent dolphin mortality event is linked to the DWH oil spill, then an opportunity may exist to establish a plan that includes the protection and restoration of dolphin habitat as well as the reduction of dolphin mortality from human activities.

The Deep Gulf of Mexico

Introduction

The final case study focuses on the GoM deep sea, defined by this committee as ocean depths of 200 m and greater (effectively beyond the continental shelf). The GoM deep sea is a

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

vast and relatively poorly understood subregion of the GoM. It is a region for which baseline and ecological production function data are relatively limited, but for which an ecosystem services approach may be particularly important. There is sufficient knowledge of deep-sea processes and availability of GoM-specific information to begin to identify ecosystem services of this deep-sea habitat, consider how these services may have been impacted by the DWH oil spill, examine methods of measuring baselines, determine what baseline data already exist for the GoM ecosystem, and identify gaps in those data. At present, the gaps in knowledge of the GoM deep-sea inhibit the ability to apply an ecosystem services approach in a quantitative way, leaving development of ecological production functions and the most effective use of valuation tools (Figure 2.1 in Chapter 2) for the future.

Finding 5.13. The deep sea is the largest yet least understood and quantitatively characterized subregion of the GoM. Because the DWH oil spill occurred in the deep sea, an assessment of the impacts of the spill cannot be complete without considering this vast subregion of the GoM.

Delineating what we do and do not know about this extensive subregion could be helpful in identifying relevant processes and uncertainties and thus directions for future investigation. The European research community, moving in this direction, highlighted the DWH oil spill as evidence of the need to develop an ecosystem services approach to evaluate impacts to the deep sea (Armstrong et al., 2011). The committee recognizes it as a unique opportunity to clarify ecosystem services of the deep sea, to identify meaningful adjustments that could be made to ongoing data collection strategies and decision making, and to highlight areas of future research. To establish a context for our discussion of the deep-sea environment in the GoM, Box 5.1 provides a brief summary of ongoing federal environmental management activities in the deep portions of the U.S. Exclusive Economic Zone.

According to our current understanding, the primary ecosystem services of the deep sea fall in the category of supporting services. In the case of the deep GoM, nutrient resupply is particularly important for overlying primary production that supports the marine ecosystem. This case study focuses on supporting services, but it also identifies ecosystem services from the other categories. The regulatory service of pollution attenuation, which is inextricably linked to primary supporting services, receives particular attention.

When considering the services of the deep GoM, it is important to identify those aspects of this system that make it unique when compared to the entire deep ocean. These distinguishing features include the flow of an oceanic gyre through silled straits (discussed below under “Supporting Services”) and the presence of extensive natural petroleum seeps and geological structures that have sequestered massive amounts of carbon as hydrocarbon and carbonate over long periods of geological time (discussed below under “Regulating Services”).

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

BOX 5.1
U.S. Environmental Protection of the Deepest Sea

When considering the utility of an ecosystem services approach to managing, protecting, and restoring the deep Gulf of Mexico, it is informative to first consider the approaches taken by various agencies that have a mandate to manage such a vast and poorly known part of the ocean system. By recognizing the 200-nautical-mile Exclusive Economic Zone (EEZ) in 1983 (Presidential Proclamation 5030), the United States extended all then-existing environmental regulations to the deepest parts of the world ocean. The U.S. EEZ is both the largest by area and the deepest of any nation, for it contains the Marianas Trench, with its world maximum depth of 10,994 m. In the deep portion of the U.S. EEZ, efforts to address particular habitats or resource issues, including (1) oil and gas development, (2) dumping (waste attenuation), (3) mining, and (4) fisheries, have been and continue to be largely disjointed. The U.S. portion of the Gulf of Mexico (GoM) is a relatively modest portion of the entire deep EEZ, with a maximum depth of only 3,600 m. Its extensive hydrocarbon deposits, however, have made it one of the most exploited and studied deep-ocean areas. Achieving effective science-based management is challenging due to the unique characteristics of the deep GoM, including novel geochemistry, slope instabilities, and steep escarpments.

Environmental Protection During Petroleum Development

The Outer Continental Lands Act of 1953, amended in 2000, has a primary intent of developing offshore hydrocarbon resources, but also includes sections requiring that the natural and human environment be protected. The Bureau of Ocean Energy Management (BOEM), in both past and current organizational configurations, carries out the mandates of the Act. Strategies for protection were initiated on the continental shelf and included restricting development where there is conflict of use, such as fishing grounds or sensitive/rare habitats. In response to industry movement into regions deeper than the continental shelf, BOEM, then known as the U.S. Minerals Management Service (MMS), established a deep-water program first outlined by Cranswick and Regg (1997) and described in more detail in a series of later reports (Baud, 2002; French et al., 2006; Richardson et al., 2004, 2008). The Environmental Studies Program (ESP) had initiated deep-water environmental studies in the mid-1980s. Based upon the benthic sampling, especially the discovery of hydrocarbon-seep chemosynthetic communities, MMS initiated requirements that industry consider habitat protection when filing exploration and development plans. Requirements undergo revision as additional information is considered by BOEM; they are communicated to the offshore industry as Notices to Lessees (NTLs).a Of special concern is the protection of historical shipwrecks (cultural artifacts), chemosynthetic communities, and deep-coral assemblages. More detail is provided in the discussion of background data for the deep ocean.

Protection from Unregulated Dumping

Prior to 1972, the extensive dumping of chemical wastes into the Gulf and the incineration of such wastes on vessels sailing the Gulf were practices endorsed by the U.S. Environmental Protection Agency (EPA) (Ditz, 1988). They were brought to an end when the U.S. Congress adopted the Marine Protection, Research, and Sanctuaries Act of 1972 (MPRSA), which applied the restrictions of the London Dumping Convention to the U.S. EEZ. The MPRSA prohibits disposal activities that would unreasonably degrade or endanger human health or the marine environment, with responsibilities assigned to EPA, the U.S. Army Corps of Engineers, U.S. National Oceanic and Atmospheric Administration (NOAA), and the U.S. Coast Guard. The offshore oil and gas industry are excluded from MPRSA coverage. The small amount of dumping that still takes place, shallow or deep, is allowed by permits requiring minimization of environ-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

mental impact. The primary dumping activity in the U.S. EEZ is dumping of dredged material created by dredging in support of navigation. All dumping of dredged material in the GoM is into shallow water.

Deep-Ocean Mining

The seafloor metallic oxide nodules found primarily in regions of the central Pacific Ocean, where sedimentation rates are extremely slow, were recognized as a potential ore for strategic metals during the cold war (Mero, 1952). The extensive habitat destruction caused by the planned strip mining gave rise to environmental concerns (Barkenbus, 1979; Gerard, 1976; NRC, 1975). Wanting to protect U.S. mining claims in international waters, yet not having ratified the Law of the Sea Treaty (LOS), the U.S. Congress passed the Deep Seabed Hard Minerals Resources Act (DSHMRA) of 1980 (P.L. 96-283, P.L. 99-507), assigning licensing and environmental regulation to NOAA. Remarkably, both the LOS and DSHMRA included the very progressive environmental policy of allowing mining to proceed only if equal areas of similar habitat, referred to as Stable Reference Areas, were preserved (NRC, 1984; Post, 1983). The LOS assigned environmental monitoring and study of these sites to the license holder, while DSHMA gave similar responsibility to NOAA. While nodule mining interest and activity within the United States has declined, the DSHMRA remains in the U.S. Code as Title 30, Chapter 26, Section 1401. This act serves primarily as a placeholder to protect a single remaining claim filed by Lockheed Martin under the Act’s provisions (National Ocean Service, 2012). Internationally, interest in seafloor mining and associated environmental protection remains high, especially for polymetallic sulfides (Hannington et al. 2008).

Deep-Ocean Fisheries and Fish Habitats

Commercial fishing for deep-ocean bottom fish is very limited in the United States, but may increase as shallow-water stocks are depleted. The Magnuson-Stevens Act (1976 and amended in 1996 and 2006) is the primary source of authority for regulation of fisheries in the United States. Initially adopted in part to bring U.S. fisheries regulation the same EEZ coverage included in the LOS, the provisions of the Act (amended in 2006) potentially cover deep fisheries. Although the Act contains no specific instructions for deep-ocean fish stocks, Title IV, Section 408 recognizes the importance of deep coral habitat. NOAA has implemented the Deep Coral Research and Technology Program to address the implementation of the Act (Lumsden et al., 2007; NOAA, 2013a). The South Atlantic Fishery Management Council has designated eight deep marine protected areas and deep-water coral habitats of particular concern. For the most part, these areas are along the shelf edge at depths as shallow as 60 m, but no deeper than 400 m (Ross and Nizinski, 2007).

On the International Front

In contrast to the United States’ fragmented program of deep-ocean management is the European Union’s highly organized approach, which adds an ecosystem services component to traditional conservation and protection (Armstrong et al., 2011; Tinch et al., 2012). Regulation of deep-sea living and mineral resources is a very active area of planning, research, and application (Gjerde, 2006). Especially noteworthy is the Convention for the Protection of the Marine Environment of the North-East Atlantic (the OSPAR Convention) in effect since 1992 (Ardron, 2008). The region of concern is far more extensive than the EEZ of Western European states, extending from the North Pole through Greenland to the Straits of Gibraltar. By 2010, 181 marine protected areas (MPAs) had been established within this large area, with six on deep seafloor in international waters (OSPAR Commission, 2010).

_________________

ahttp://www.boem.gov/Regulations/Notices-To-Lessees/Notices-to-Lessees-and-Operators.aspx.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Supporting Services

The supporting services of the deep GoM are greatly influenced by the semi-enclosed nature of the basin, which produces locally unique conditions. At the same time, the GoM is tightly coupled to the larger Atlantic basin by the powerful surface currents that flow through its two straits. Processes of the deep GoM thus provide supporting services on a local scale and on a much larger proximal scale. The following discussion first considers water circulation and exchange in the GoM as critical to understanding oxygen and nutrient resupply (in support of primary productivity) and then addresses nutrient resupply and natural and oil-impacted microbial processes that determine or influence these services.

Water Circulation and Exchange

As reviewed in the Interim Report (NRC, 2011), water circulation in the GoM consists of a relatively high-velocity, rapidly mixed upper layer and a low-velocity, slowly mixed lower layer. Transfer of oxygen, dissolved nutrients, heat, and momentum between the upper and deeper layers is limited by density stratification. The circulation and exchange of the GoM has two special aspects. First, the GoM is an important segment of the intensified western boundary current of the North Atlantic Gyre, receiving strong flow from the Caribbean and on through to the Atlantic. This Gulf Loop Current links the surface water to the larger Atlantic and causes local processes to have far-distant effects. Presumably, much more will be learned about transport and mixing from the extensive studies following the DWH oil spill.

Second, the deep thermohaline circulation of the GoM is influenced by the sill depths of the basin, connecting to the Caribbean in the south through the straits of Yucatan, with a sill depth of approximately 2,040 m, and to the Atlantic to the east through the Florida Straits, with a sill depth of approximately 740 m. Water flows out of the GoM only through the Florida Straits, where the depth of the sill restricts the flow. The 1,300-m difference between the depth of the Yucatan sill and the Florida sill sets up a deep-flow regime that is not fully understood. Sturges (2005) review of deep-flow data for the Caribbean and GoM supported previous suggestions that flow through the straits of Yucatan consists of cold flow into the Gulf balanced by an equal but somewhat warmer outflow created by mixing enhanced by the topography of the sill. These two-way deep flows traverse the Caribbean and connect to the open Atlantic via the Windward and Anegada-Jungfern passages.

These circulation patterns may contribute to unusually high levels of oxygen in depths of the GoM below 500 m. The water column of the deep GoM has a moderate oxygen minimum of approximately 2.5 ml/L at a mid-water depth of about 500 m, compared to levels greater than 5.0 ml/L at greater depths (Rivas et al., 2005). High levels of oxygen below the oxygen minimum in the deep GoM (despite active biological consumption and topographic restriction) can only be explained by frequent “ventilation,” the inflow of oxygenated water from the Caribbean matched by an outflow of older deep water. Such deep exchange is only possible through the Yucatan Channel because of the shallower sill depth of the Straits of Florida and the upper-water outflow there.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

The Yucatan Channel is now recognized to be a two-way passage, with deep water leaving and returning after some residence period in the GoM (Rivas et al., 2005, 2008; Sturges, 2005). Estimates of deep-water residence times vary. Shiller (1999) reviewed estimates and set residence time in the eastern GoM at 50 years and the western GoM at 270 years. This range is consistent with a model-based rate of 100 years (Welsh and Inoue, 2002). A 100-year period for the turnover of water in the semi-enclosed GoM is short, relative to open deep-sea basins, and helps to explain maintenance of the oxygenated and nutrient-rich state of the deep GoM, yet long compared to the generation times of marine organisms and their ability to be resilient in the face of stressors or disturbances that lead to oxygen or nutrient depletion in deep waters of the GoM.

Nutrient Resupply in Support of Primary Productivity

The most extensive studies of primary productivity in the GoM have been carried out in shallow coastal waters, especially associated with the discharge of the Mississippi River. High levels of productivity have been observed over the deep GoM using sea-surface color imagery (Biggs et al., 2008; Müller-Karger et al., 1991). Regions of transient high productivity are associated with the Gulf Loop system, which can cause upwelling (and thus nutrient resupply) when impinging on the shelf break and at the junction of gyres. Primary productivity in waters over the deep GoM supports the larger marine ecosystem; upwelling or other mechanisms that resupply nutrients (e.g., inorganic sources of nitrogen and phosphorus) depleted during photosynthetic activity are essential to continuing that support. The fraction of surface production not transferred to higher trophic levels in surface waters (or recycled there) is exported to the deep GoM, where it supports the extensive benthic heterotrophic communities that dwell there (Rowe et al., 2008).

The oxygenated state of the deep waters in the GoM, coupled with the availability of methane and hydrocarbon-associated hydrogen sulfide emerging from natural seeps, supports another form of (nonphotosynthetic) primary productivity: chemosynthesis by prokaryotic microbes, particularly symbiotic chemosynthetic bacteria that support whole communities of metazoans such as tubeworms and mussels (Cordes et al., 2009; Orcutt et al., 2005). Seafloor seepage from extensive hydrocarbon reservoirs through an unknown number of sites, even if individually of limited spatial scale, makes the deep GoM one of the most chemosynthetically productive regions of the world’s oceans. These seeps clearly support a dense mix of endemic and nonendemic fauna (and microflora) that exploit the emerging resources. Actual productivity rates are unknown, but the substantial age of some metazoans indicates that the biomass pools have accumulated very slowly (Cordes et al., 2009). Trophic web tracing using stable isotopes has identified some transfer of chemosynthetic carbon and nitrogen to the surrounding normal (heterotrophic) benthic and pelagic animals, but this export is localized and few species have been documented to participate in these cross-habitat links (Carney, 2010; Cordes et al., 2010; Demopoulos et al., 2010; Macavoy et al., 2005).

Lacking photosynthesis entirely, and despite the localized bottom areas of chemosyn-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

thesis, the deep GoM is primarily a region of respiration, the process by which heterotrophic organisms (from aerobic bacteria to all higher organisms) consume oxygen and release carbon dioxide from the organic matter on which they feed. The primary source of organic matter in the deep sea is photosynthetic detritus that sinks from surface waters; respiration of this material not only releases carbon dioxide, but also inorganic nutrients essential to resupplying and thus supporting photosynthetic primary production in surface waters. To a presumably lesser (but unknown) extent, seeping hydrocarbons are also respired; importantly, given the nitrogenpoor status of hydrocarbon compounds, they are respired without an appreciable release of inorganic nitrogen to support primary production. Indeed, oil-degrading bacteria, whether responding to naturally seeping or “spilled” hydrocarbons, must take their required nitrogen from the resupply pool in order to consume and respire the hydrocarbons.

Comparative measurements on samples collected from inside and outside of the deep oil plume emanating from the Macondo well site provide clear evidence of early and significant nitrate depletion within the plume coincident with hydrocarbon degradation, with nearly twice as much nitrate consumed as oxygen (Hazen et al., 2010). No evidence for a compensatory response by nitrifying bacteria or Archaea (microorganisms responsible for generating new nitrate from reduced forms of nitrogen, particularly ammonia, in the deep ocean) was observed, nor was the concentration of ammonia inside the deep oil plume statistically distinguishable from that in surrounding deep water (Hazen et al., 2010).

An increase in the baseline of hydrocarbon respiration in the deep GoM may thus translate to a reduction in the resupply of nitrogen (particularly nitrate) to the surface ecosystem, yet estimates of that baseline, whether static or fluctuating, are lacking, as are evaluations of any long-term or persistent impacts of the DWH deep oil plume on the available nitrate pool. Suitable models to identify the linkages and balances between these various processes are also lacking. Some existing models, targeting other goals such as trophic transfers of carbon and nitrogen (Rowe and Deming, 2011; Rowe et al., 2008; Wei et al., 2012a), may provide starting points for developing the more complex systemwide models ultimately required to evaluate supporting ecosystem services of the deep GoM.

Biological Interactions: Resilience and Habitat Diversity

The deep GoM is a very large and low-turnover subsystem that provides the whole ecosystem with greater resilience (see Chapter 3 for definitions and a discussion of resilience). This role is especially obvious with respect to nutrient recycling. In systems where plants have direct access to nutrient uptake, the available supply of nutrients may fluctuate in an unstable manner. Being aphotic and vastly larger than the photic zone, the deep GoM provides a resupply of nutrients at a rate totally independent of the photic zone’s biological demand and is thus a very stable source of nutrients to overlying life. Although the DWH blowout triggered more research on hydrocarbon-degrading bacteria and their reactions to dispersants used in the deep GoM (see Chapter 4), investigations of nutrient-regenerating microbial processes (e.g., the production of nitrate from ammonia) essential to stable long-term support of overlying productivity appear to be lacking.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

When considering ecosystem services, it is important to note that the deep GoM is not homogeneous, but has several special seafloor habitat types—hydrocarbon seeps, massive carbonate platforms, and complex mud bottoms—which figure in the discussion of other ecosystem services (below). The seep habitats are best studied and comprise a suite of chemically and morphologically distinct habitats associated with hydrocarbon and brine seepage. These habitats are widespread in the northern GoM and can be categorized as ranging from fluid- to mineral-prone (Roberts and Carney, 1997). The fluid-prone habitats have ongoing effluxes of methane, liquid hydrocarbon, and/or brines. The mineral-prone habitats have accreted massive carbonate hardgrounds over a long period of microbial anaerobic hydrocarbon oxidation. The chemosynthetic ecology of the fluid-prone systems has been studied extensively since discovery (reviewed by Fisher et al., 2007). Research on the heterotrophic ecology of the carbonate hardgrounds is under way in conjunction with efforts to protect deep coral and relate potential impacts from oil and gas development (Becker et al., 2009; Sulak et al., 2008).

The full complexity of the extensive mud bottom is only slowly being recognized because of its vast size and the difficulty in detecting spatial or temporal differences in its biological processes. Bathymetric zonation of biota is the most obvious form of habitat heterogeneity on a regional scale (Wei et al., 2010b). On a more local scale, geological processes may create ecologically unique habitats. In the northern GoM, the continental slope is topographically complex, with many small basins and ridges. The ecological consequences of this topography have yet to be effectively examined. The slope is made additionally complex by extensive submarine landslides and megaslides that create seafloor scars where geochemically older sediments are exposed to seawater and biological colonization. The same slides also produce large deposits of slide material that entomb geochemically young sediments. Because submarine landslides pose both a hazard to oil drilling and a tsunami risk, their geophysics are being actively explored, but the ecological and ecosystem services aspects of deep-water slides are virtually unknown (Mienert et al., 2003; ten Brink et al., 2009). Massive carbonate habitats, unrelated to sites of hydrothermal activity, are comprised of the nearly vertical walls of the carbonate platforms of west Florida and the Yucatan. These platforms represent one of the most extensive deep hardground habitats in the world’s oceans (Poag, 1991). Study of the ecology and biodiversity of these deep habitats is in its infancy.

Its location within the larger North Atlantic circulation and its abundance of special habitats make the deep GoM a likely source—and center of distribution—for seep and hardground fauna. This conjecture is now under examination.

Finding 5.14. The deep Gulf of Mexico’s supporting services of water circulation and stable nutrient resupply to the photic zone and regulating service of gas and climate regulation are of broad benefit to all people. These provide large-scale and long-term benefits that involve the entire global ocean. Additionally, the deep biota may play a critical role in maintaining the diversity and resilience of the larger Atlantic Ocean.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Regulating Services

Pollution Attenuation The ecosystem service of pollution attenuation as it pertains to hydrocarbon degradation (breakdown to smaller organic compounds) is well documented for shallow marine and intertidal environments (see Chapter 4), but was unknown for the deep-sea water column prior to the DWH oil spill. The release of crude oil from the spill site, creating a plume of hydrocarbons in the deep GoM, provided unique impetus and resources for a scientific evaluation of the ability of natural communities of marine bacteria to attenuate hydrocarbons in situ in deep water. Several groups of researchers, working on different ships and at different times from the start of the oil spill, documented the indigenous microbial response to this deep-sea plume by comparing microbial abundance, diversity, and selected activities inside the plume with similar attributes of the surrounding deep water (Camilli et al., 2010; Hazen et al., 2010; Mason et al., 2012; Valentine et al., 2010).

Within several weeks of the initial accident, the total number of bacteria inside the plume was twice as high as in surrounding waters (5.51 x 104 cells ml-1 compared to 2.73 x 104) and bacterial community diversity had dropped (Hazen et al., 2010), with known hydrocarbon degraders becoming dominant (Abbriano et al., 2011; Lu et al., 2011: Valentine et al., 2010). Of particular importance were species of Oceanospirillales, a genus known to degrade simple aliphatic hydrocarbons; Cycloclasticus (“ring-breaker”), a genus first discovered in marine sediments, named for its ability to degrade complex aromatic hydrocarbons (Dyksterhouse et al., 1995), and known to occur in GoM waters prior to the DWH oil spill (Geiselbrecht et al., 1998); and Colwellia, a genus first described from nearby deep Caribbean waters for adaptation to the low temperature and high pressure of the deep sea (Deming et al., 1988). The latter two groups were confirmed experimentally to degrade hydrocarbons in seawater samples collected directly from the oil plume in the deep GoM (Redmond and Valentine, 2012). Microbial community succession was thus deduced from available studies conducted during the spill (Abbriano et al., 2011) to proceed from dominance by Oceanospirillales in the first weeks, to Cycloclasticus and Colwellia by June, and to methanotrophic (methane-oxidizing) genera, including Methylococcaceae, Methylophaga, and Methylophilaceae, by September. This succession implied that the sequential process for pollution attenuation was degradation of simple hydrocarbons, followed by more complex hydrocarbons, and finally methane gas (Kessler et al., 2011). Within-plume measurements of oxygen consumption, inherent to all of this microbial study, fell short of a depletion level that would threaten fisheries (Camilli et al., 2010). Indeed, as oxygen (and nitrogen) is depleted in the water column, the causative microbial activity itself will slow.

Finding 5.15. Attenuation of the DWH oil spill by natural populations of deep-sea oil-degrading bacteria represents a novel interpretation of this category of ecosystem service, and one of potentially high value in an overall cost-benefit analysis of the impacts of the DWH oil spill.

The deep waters of the GoM clearly provide the ecosystem service of pollution attenuation that can foster or enhance hydrocarbon bioremediation. A valuation of this service could be

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

attempted based on an estimate of the amounts of hydrocarbons degraded in the plume and the costs of other means of attenuating that amount. The valuation would also require some understanding of the known costs of other remediation efforts and where they were applied (Chapter 4). Complicating such a valuation is that other attenuation means are not typically compound specific, just as in situ bioremediation can leave many components of crude oil unaltered.

Marine sediments in the deep GoM, as hosts to natural hydrocarbon seeps, harbor marine bacteria capable of degrading hydrocarbons (Geiselbrecht et al., 1998; Orcutt et al., 2005). Until recently, this capability was understood to be dependent on the availability of dissolved oxygen, supplied from overlying oxygenated water, as it is in other marine environments. Oxygen depletion events would slow or halt hydrocarbon attenuation. If indeed restricted to oxygenated settings, then the tradeoff between pollution attenuation and oxygen consumption would place limits on the value of this ecosystem service in marine sediments, where only upper sediments near the sediment-water interface remain oxygenated. Recent research on hydrocarbon degradation within anoxic strata of marine sediments, including from the deep GoM, clarifies that degradation can proceed in the absence of free oxygen through the activities of newly discovered sulfate-reducing bacteria (Kniemeyer et al., 2007). Severe oxygen depletion would be required in the water column (e.g., in the oil plume) to allow the activities of these anaerobic bacteria to dominate, but natural communities of heterotrophic sulfate-reducing bacteria perform near continuously within the oxygen-depleted strata of the sediments that blanket the GoM floor. Unknown is whether the specific types of hydrocarbon-degrading sulfate-reducing bacteria discovered at natural oil seeps in the GoM (Kniemeyer et al., 2007) also occur throughout the other anoxic sediments of the GoM, including those impacted by the DWH oil spill.

Just as indigenous hydrocarbon-degrading bacteria responded to an injection of oil into deep waters (Abbriano et al., 2011), indigenous hydrocarbon-degrading bacteria in oxygenated surface sediments, and potentially within anoxic strata, may be attenuating pollution in the formation of deposited hydrocarbons, even if slowly or intermittently over time. Deposits of undegraded hydrocarbons from the DWH oil spill onto sediments (Joye, 2013; Joye et al., 2011) will be buried rapidly by bioturbation (the oil sequestered in mud-dwelling animal burrows) and over time by natural sedimentation processes. Buried oil will continue to be subjected to long-term attenuation by bacteria dwelling within the sediments. The limits on hydrocarbon bioavailability over time (as described in Chapter 4) may be partially alleviated by surfactants produced naturally by sediment-ingesting biota (Mayer et al., 1996).

Deep muds of the GoM thus provide an ongoing ecosystem service of pollutant attenuation that is currently understood only in limited, largely qualitative ways. Baseline information on the magnitude of in situ hydrocarbon degradation by marine bacteria inhabiting the vast seafloor sediments of the deep GoM is not available. Obtaining measurements of in situ rates of hydrocarbon degradation in GoM sediments and scaling the impacts accordingly would facilitate a quantitative valuation of this ecosystem service. Methods to estimate in situ rates exist, as applied to evaluations of the fate of pollutants more toxic and recalcitrant than light-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

crude hydrocarbons (e.g., phenanthrene) in coastal marine sediments elsewhere (Tang et al., 2006).

Pollutant Attenuation Valuation

Valuation of pollutant attenuation (or waste treatment) by natural systems in theory is not difficult and in practice has been conducted primarily in fresh- and saltwater wetlands for the coastal and marine environment (Breaux et al., 1995; Kazmierczak, 2001; Su and Zhang, 2007). Studies focusing on pollutant attenuation/waste regulation primarily rely on the replacement cost or treatment cost approach. As described in the Interim Report (NRC, 2011), this approach calculates the cost of providing the ecosystem services, such as pollutant attenuation, in an alternative way, such as replacing the service provided by ecosystems with a human-engineered approach. This approach only focuses on cost and therefore is not a direct measure of benefits, except in very rare circumstances: (a) when there is no difference in the quantity and quality of the service; (b) the engineered alternative is the least costly; and (c) society demands these services (Shabman and Batie, 1978).

Determination of the suitability of the replacement cost or treatment cost approach to quantify the value of pollution attenuation, specifically hydrocarbons, requires confirmation that the GoM can perform this service and that society needs this service.

As described earlier in this case study, the GoM is well equipped to handle the breakdown of hydrocarbons into smaller organic compounds. Hydrocarbon-degrading bacteria, present in the plethora of natural seeps in the deep GoM, responded rapidly when the plume was formed, which demonstrated that the GoM environment does have the ability to attenuate pollution, specifically hydrocarbons. Has society expressed a need for this service? Given the legal requirement under NRDA to “make the public whole” and the spill responses detailed in Chapter 4, society expects that the pollution will be “cleaned up.” The remaining question is: What would be the engineered equivalent of the services provided by the interaction of indigenous microbes and nitrogen recycling metazoans at depth? The techniques utilized to clean up surface oiling are well understood (see Chapter 4), but at depth, where the plume formed, it is unclear what current technology could be dispatched to “clean” the deep. However, in this case, damage to the service did not take place, nor was evidence of a limiting factor observed (nitrate was consumed during the service but not depleted). The service became manifest given the presence of the hydrocarbons. Therefore, the value to be calculated would not be for an NRDA assessment. Rather, it would be the benefit that society receives from the presence of hydrocarbon-degrading bacteria as characterized by the ecosystem services approach in Table 5.8, below.

The benefits derived from GoM pollutant attenuation have changed over the past several decades. For many years, coastal communities and inland chemical industries benefited from low-cost ocean disposal of wastes under the assumption that dilution of the pollutants by the marine waters provided a degree of protection from the toxicities of those pollutants. More recent recognition of environmental damage has since resulted in additional restrictions on

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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TABLE 5.8 Provision of and Valuation for Deep Sea Pollution Attenuation

NRDA Practices

Resource Deep Sea
Typical approach to assessment Not previously assessed

Valuation Under the Ecosystem Services Approach

Ecosystem Service Pollutant Attenuation
Type of data needed for ecological production function

A. Circulation and mixing models.

B. Rates of microbial attenuation of pollutants.

Ecological production function

1. Relationship between physics, geomorphology, and microbial degradation to estimate the rate of natural removal of pollutants.

Type of data needed for valuation

1. Engineered cost for pollution removal.

2. Amount of hydrocarbons released and available for attenuation.

3. Attenuation rates.

Valuation method Replacement cost: Calculate the cost of engineering a similar pollutant removal process that is provided by the deep ocean.
Type of data needed for valuation of ecosystem service

1. Data on (A) and (B) would be required to understand the potential pollution attenuation rates.

2. Cost data and rates of engineered attenuation equivalent to what is being provided by the deep ocean.

  This approach, while theoretically possible, might be difficult to employ given the scale of the deep ocean and the ability to effectively measure the amount (and specific components) of pollutant that was attenuated.

polluting activities, but ocean discharge of processed wastes is still a critical component of water management plans in the GoM region. In the specific case of partial attenuation of deepwater oil spills, stakeholders that are able to continue exploiting deep oil sources after a major accident will still be able to benefit.

Greenhouse Gas and Climate Regulation

The climatic influence of the GoM sea surface on the eastern two-thirds of North America is profound, yet identifying special roles of the deep GoM in greenhouse gas and climate regulation is challenging. Certainly the amount of hydrocarbons commercially extracted from the deep GoM and subsequently burned throughout North America contributes to greenhouse gases well above natural levels of seepage. The unusual geomorphology and physical oceanography of the deep GoM may give it important roles in nutrient resupply, a critical supporting service of the deep sea, and thus in carbon dioxide fixation and carbon sequestration.

The important question of whether the deep Gulf is a net repository or source of carbon to

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

the ocean and atmosphere, however, is unresolved. Several lines of evidence suggest that the GoM sequesters more than the average amount of carbon in its sediments. First, the GoM lacks the great depth needed to dissolve biogenic carbonates, thus entombing these planktonic particles in the thickening sedimentary column. Second, the high sedimentation rates on the continental slope near the Mississippi River (Santschi and Rowe, 2008) allow for greater preservation of organic detritus. Third, the massive deep carbonates of the West Florida and Yucatan escarpments indicate a high rate of sequestration over geological time. Last, the prevalence of microbially deposited carbonates within the sedimentary environment (mediated by methane-consuming bacteria in sulfide-rich strata) illustrates a long-term conversion and sequestration of seeping hydrocarbons. The extent to which an oil spill of the magnitude of the DWH oil spill may impact seafloor carbon sequestration (or hydrocarbon attenuation) in the deep GoM is unknown.

The argument that the GoM is a net exporter of carbon would seem to be supported by the increasing information on the spatial extent and seepage rates of natural hydrocarbon seeps. Actual rates remain speculative, but surface slicks caused by liquid hydrocarbons can be effectively mapped using synthetic aperture radar (SAR) (MacDonald et al., 1996) and are being found to be prevalent over offshore oil deposits. Detection of methane bubble plumes rising from the seafloor has now become much more effective with multibeam sonar systems (Weber et al., 2011).

Another potentially important greenhouse gas–regulating role may be performed by members of the deep GoM microbial ecosystem. Based on the strength of the methane-consuming response of methanotrophic microorganisms to the DWH oil spill, and the likelihood that methanotrophic microorganisms are prevalent throughout the deep GoM due to natural seepages, Kessler et al. (2011) suggested that the deep GoM provides a “dynamic biofilter” to large-scale methane releases in the deep, whether natural (e.g., from methane hydrates) or by accident. Methane ranks among the most potent of greenhouse gases. Evaluation of this regulating ecosystem service requires further investigation into the prevalence and rates of microbial methanotrophic activity in the deep GoM. Tradeoffs with the supporting services of the deep GoM, in particular nitrogen resupply to primary productivity, also need to be examined specifically in relation to methanotrophy.

Provisioning Services

Finfish, Shellfish, Marine Mammals Provisioning services of the deep GoM seafloor are currently minimal, although deep-water finfish species, commercially fished in the Atlantic Ocean, are present. There is a limited and intermittent fishery for deep shrimp marketed as “royal reds.” The surface waters overlying the deep GoM provide commercial and recreational harvests of large migratory finfish such as the bluefin tuna. The question of how the deep GoM interacts with the rich fisheries of the shallow GoM is open and in need of investigation. The old presumption that the shallow and deep are largely isolated from one another is not necessarily correct.

An example of an unexpected link between shallow and deep can be seen with deep-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

foraging marine mammals. Offshore upper waters support diverse populations of cetaceans that are generally distinct in species composition from those in continental shelf waters. Modern tagging technology is providing insight into the extent of deep foraging by predatory whales (Arranz et al., 2011). The deep scattering layer in the water column and the benthic boundary layer are both concentrating features for prey organisms exploited by cetaceans diving from the surface to depths as great as 1,500 m. Gouge marks in the sediments of mud volcanoes as deep as 2,100 m in the eastern Mediterranean have been attributed to Cuvier’s beaked whales (Woodside et al., 2006); similar marks characteristic of Cuvier’s and other beaked whales have been reported for the GoM. Cetaceans have not been commercially harvested in the GoM since the early 1900s.

As discussed in the fisheries case study, impacts on the lower levels of the trophic web have the potential to cascade up to the surface-dwelling species, which exploit the deep aggregations of living biomass at the deep scattering layer and the sediment-water interface (Abbriano et al., 2011; Kaltenberg et al., 2007). Such impacts, if they occur, might be detected by a combination of short-term and long-term population monitoring.

Finding 5.16. The Macondo well blowout had the potential for creating both lethal and nonlethal impacts on deep-sea species of potential future commercial value and upper-ocean species now commercially harvested.

Energy Oil and Gas

The U.S. EEZ in the GoM is the major offshore oil and gas production region in the United States. Historically, the continental shelf provided most of these hydrocarbons, but a transition is now under way, with the greatest contribution to energy production currently coming from depths greater than 200 m. The DWH blowout and persistent spill caused a loss of commercially valuable hydrocarbons, resulting in a decreased value of the formation where the drilling occurred. Relative to the combined value of all deep GoM reservoirs, the loss of commodity can be seen as small. The blowout did, however, alter the regulatory environment and cause temporary delays in new production through drilling moratoria and extended permitting times (NRC, 2011). The extent to which better-regulated and safer exploitation negatively or positively impacts the provisioning service remains to be seen.

Of the provisioning services, oil and gas extraction and production contribute significantly to the region’s economic productivity. Socioeconomic impacts of offshore oil in general and deep-water oil in particular have been assessed by BOEM research programs and are monitored on a 5-year basis (Petterson et al., 2008; Tolbert, 2006). Each stage of deep-water development, from exploration to production, employs a wide range of experts and results in the contracting and hiring of salaried and wage workers both within oil companies and in the supportive service industry. The populations that benefit from these provisioning services includes geologists, petroleum engineers, and structural engineers as well as offshore workers who operate drilling rigs, production platforms, and support vessels.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Chemical Production

The GoM was once a major source of elemental sulfur extracted as a molten liquid by super-heated steam (the Frasch process), but the last offshore facility ceased operation in 2000 because sulfur could be recovered more cheaply as a byproduct of ore processing (Kyle, 2002). Fossil-water brines extracted along with oil are a potential source of halides, but they are currently discharged into the ocean and regulated as toxic waste. The prevalence of the petrochemical industry in the northern GoM coastal zone is not due solely to the proximity of hydrocarbons. Salt domes within the zone are mined for halogens, primarily chlorine, by means of hydraulic dissolution. Chlorinated hydrocarbons are produced as solvents and feedstock for plastics manufacturing. The GoM is so geologically complex because of salt tectonics that the presence of igneous and hydrothermal ore bodies cannot be discounted. With the exception of a few xenoliths, exotic basement rock carried upward by salt movement (Stern et al., 2011), no deposits have been found to date. The DWH blowout did not impact the existing chemical industry or potential deep GoM chemical industry, but an increased regulatory environment for oil and gas exploration will eventually impact these industries.

Cultural Services

Aesthetics and Existence

When you stare into the abyss the abyss stares back at you.

Friedrich Nietzsche

     I asked them to look into the Abyss, and, both dutifully and gladly, they have looked into the Abyss, and the Abyss has greeted them with grave courtesy of all objects of serious study, saying: “Interesting, am I not? And exciting, if you consider how deep I am and what dread beasts lie at my bottom. Have it well in mind that a knowledge of me contributes materially to your being whole, of well-rounded, men.”

Lionel Trilling, 1961 essay “On the Teaching of Modern Literature”

As Lionel Trilling’s essay describes, the Abyss has become a powerful metaphor in recent literary history. Vast, dark, and inhabited by seemingly terrible beasts, to Nietzsche it stood for total meaninglessness, but to the more modern writer with a nod to oceanography, it is fascinating. The public at large retains a fascination with the deep ocean and its exploration by pioneers such as William Beebe and modern visionaries such as James Cameron. There is a spiritual or cerebral satisfaction in knowing deep-sea animals or ecosystems exist, evidenced by the unwillingness to use marine mammals as a source of food and measurable as the willingness to pay for conservation.

It can be argued that the deep GoM, as with the entire vast and remote deep ocean floor, has a high existence value, but this argument requires an examination of how high that value is perceived to be. The usual pattern in society is to ascribe a high existence value to habitats

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

that are both desirable in some manner as well as dwindling in supply. Thus, there is often an implied connection between perceived value and rarity.

Preservation of scenic wilderness otherwise threatened by overly exploitative encroachment in the National Park System is a prime example. Protection of a watershed to ensure the survival of a rare endangered species in either a technical or legal sense is another. Rare species abound in the deep ocean, and they are endangered by ongoing and planned resource exploitation that includes destructive trawling and habitat removal similar to strip mining (Carney, 1995; Ramirez-Llodra et al., 2011). The deep ocean is certainly wilderness, and human experience will be restricted to telepresence, except for scientists working with government support and explorers with access to substantial wealth. However, the vastness of the deep sea, the largest ecosystem on the planet, combined with the low level of human awareness of the system have the effect of making the existence value of the system unrecognized. Public interest and curiosity have somewhat effectively been focused on special subsystems such as hydrothermal vents, hydrocarbon seeps, and coral-supporting deep hardgrounds, but these are a tiny fraction of the total area of the deep seafloor. For management of the vast mud bottoms, the assumption of homogeneity has been clearly proven wrong by existing information on zoogeography and biodiversity (Menot et al., 2010; Rex and Etter, 2010).

Cultural Artifacts

Submerged cultural artifacts in the deep GoM provide an aesthetic benefit to people. The lifetime of such artifacts is prolonged by conditions in the deep sea (e.g., colder temperatures, higher pressure, reduced rates of biological activity) compared to those in shallow waters, making the extended preservation of submerged cultural artifacts an ecosystem service of the deep sea. MMS/BOEM includes in its responsibility the protection of cultural artifacts under the provisions of Section 106 of the National Historic Preservation Act of 1966. The initiation and early implementation of the program in the GoM and decisions about necessary technology were fully explained by Irions (2002).5 In the deep GoM, cultural artifacts consist primarily of shipwrecks that occur at all ocean depths, although usually clustering on the continental shelf along navigation routes between ports. More than 400 shipwrecks dating from 1625 to 1951 have been verified (BOEM, 2010) in the GoM. The deep GoM shipwrecks represent a broad historical span from colonial times to World War II, including the sinking of a German U boat.

Especially noteworthy cultural artifact studies supported by MMS/BOEM are Church et al. (2007) and Church et al. (2009), which were carried out by multi-institutional partners, including oil companies and the offshore service industry. These studies have led to the formulation of more effective archaeological survey techniques employing high-resolution seismics and the implementation of spatial restrictions intended to provide protection for the artifact. In most cases, industry submits the required surveys to BOEM as part of the permitting process,

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5 Current information about the program is available online at http://www.boem.gov/Environmental-Stewardship/Archaeology/Gulf-of-Mexico-Archaeological-Information.aspx. This link provides access to relevant documents such as survey requirements placed on industry in 2005 and revised in 2011.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

although BOEM does support surveys for its own use. Industry-collected survey data are considered proprietary, but they have been shared with independent researchers on occasion. The coordinates of shipwrecks are not shared with the public because of concerns about site destruction. The BOEM Gulf of Mexico Archaeology program continues to be proactive in outreach to make the public aware of the deep artifacts. This effort is carried out through the agency’s websites and through partnerships with the NOAA Ocean Exploration Program.

Deep-water oil and gas activities have definitely increased knowledge of submerged artifacts due to discovery and investigation using the advanced tools of the industry. BOEM specifications for survey and safe distances during development afford a high degree of protection. Impacts to artifacts caused by a seafloor blowout are probably limited to damage of physical structures in proximity to the well. No report of damage to a submerged cultural artifact has been reported as a result of the DWH oil spill.

Impacts of the DWH Spill on the Deep Sea

Simplistically and under ideal circumstances, environmental impacts are assessed through comparison of baseline data for the before-impact state to data for the after-impact state (Schmitt and Osenberg, 1996). The degree to which pre-spill data constitute an adequate baseline requires a more complex examination than can be undertaken here. The data for possible impacts are considered first, followed by the data that constitute the available baseline. Much of the study of the impacts of the DWH oil spill on the deep sea has been conducted under the auspices of the NRDA process, and, at the time of this writing, the full NRDA results for the deep GoM have not been released. A general account of deep-sea activities is available in a status report of April 2012 (NOAA, 2012b). More detailed findings from 2010 are included in Operational Science Advisory Team’s 17 December 2010 Summary Report for Sub-Sea and Sub-Surface Oil and Dispersant Detection: Sampling and Monitoring (OSAT, 2010).6 Research cruise activities have overlapped, but generally it can be said that water column sampling with the intent of detecting oil and understanding its trajectories began in early May 2010, with a later inclusion of faunal studies that might allow for the assessment of impacts. Taking advantage of ongoing deep-coral studies, a work plan was accepted in July 2010 for NRDA investigation of that habitat based primarily on imaging and observation of hardgrounds in the vicinity of the spill. Related investigations of hardgrounds have continued into 2012.

During phase I, May–August 2010, approximately 4,000 water and sediment samples, taken at depths greater than 200 m, were collected offshore with the primary purpose of detecting and quantifying the presence of spilled oil. These samples provided the basis of findings in OSAT (2010), in which hydrocarbon levels were consistent with those from submerged-plume models and rarely exceeded levels associated with injury except within 3 km of the blowout site.

Plans for investigation of soft-bottom impacts were put forward in July 2011 (Deepwater Benthic Communities Technical Working Group, 2011). These involved new sampling and

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6 Partially redacted study plans are available at http://www.gulfspillrestoration.noaa.gov/oil-spill/gulf-spill-data.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

analysis of 65 sites selected from previous studies: 17 within 3 km of the spill, 23 within 25 km, 15 sites more than 25 km away along the modeled route of a deep hydrocarbon plume, 2 sites more than 25 km under the known route of the surface slick, and 8 reference sites previously sampled in the Deep Gulf of Mexico Benthos (DGoMB) study (Rowe and Kennicutt, 2009). The sampling resembled traditional infaunal surveys with supporting geological and chemical analysis. A multicorer was proposed as the primary sampling device. Supplementing these traditional deep-sea approaches has been the use of a sediment-profiling camera, a device useful for assessing the thickness of deposited layers. Macrofauna would be examined at each site in three cores with a surface area of 0.03 m2, and meiofauna from a single core with an area of 0.01 m2. A workplan to investigate large animals living on the sediment surface at 10 sites using remotely operated vehicle (ROV) imaging surveys of bottom and water column was approved in October 2011.

Plankton studies were initiated offshore in November 2010, but they seldom included samples deeper than the 200-m upper limit of the deep ocean. A work plan to sample deep mesopelagic and bathypelagic fish using midwater trawls was submitted on November 30, 2010.

In terms of the supporting and regulating ecosystem services, the primary impacts to the deep system will include reductions of dissolved oxygen and nitrate and toxic effects on biota. A blowout at the seafloor of a deep-water oil well has been recognized by regulatory agencies as a worst-case scenario since the onset of deep drilling (Carney, 1998), with the subsurface behavior of plumes examined during an experimental release (Johansen, 2000). Study of the acute effects on the deep-water column, deep bottom, and surface were initiated as part of the NRDA process as well as by separately funded independent scientists. As noted earlier, NRDA findings were not public as of this writing, but publicly available, peer-reviewed results provide a basic scenario. Because the hydrocarbons forcefully jetting into the bottom waters consisted of a wide range of particle sizes, a subsurface plume of slowly rising droplets as well as a soluble fraction was expected. Camilli et al. (2010) confirmed and documented this expectation, with little early indication of microbial consumption and associated oxygen reduction. An extensive amount of soluble component was subsequently reported (Reddy et al., 2011), as well as microbial consumption accompanied by drawdown of oxygen (Camilli et al., 2010; Valentine et al., 2012) and nitrate (Hazen et al., 2010). Thus, the DWH oil spill is highly likely to have impacted regional gas exchange and nutrient dynamics. Hydrocarbons, unlike natural detritus, lack nutrients such as nitrogen and phosphorus. Microbial shifts to consuming hydrocarbons will thus alter the cycling of these essential nutrients. Larger-scale mixing will reduce these impacts over time. Such an event was anticipated and modeled by BOEM-supported researchers prior to the spill using the smaller Ixtoc 1 oil spill from 1979 as an input example, along with mixing models of the GoM (Jochens et al., 2005).

Among the damage assessments for the water column, mud bottoms, and hardgrounds, only results for the latter two have been reported. At the time of the blowout, the MMS (now BOEM) was supporting exploration and study of deep coral aggregations in the northern GoM in conjunction with regulation development. That effort was redirected to impact assessment. Dead and dying corals with brown, flocculent material on them were reported, which was

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

reasonably attributed to exposure to hydrocarbon/dispersant plumes (White et al., 2012). Three months after the Macondo well was capped, nine sites of deep-sea coral communities, located more than 20 km from the well and at depths of 290 to 2,600 m, were investigated using a ROV, the Jason II (White et al., 2012). These sites included seven that had been observed in 2009, and all were healthy, showing no impact from the spill. However, one site at 11 km southwest of the well and 1,370 m deep, which would have been in the path of the hydrocarbon plume, was covered by brown flocs and had coral colonies exhibiting obvious signs of stress such as bare skeleton, tissue loss, sclerite enlargement, excess mucous production, and abnormally colored or malformed commensal ophiuroids (White et al., 2012; WHOI, 2012). Of 43 corals, 46 percent showed impacts extending to more than half of the colony, and 25 percent showed impacts exceeding 90 percent of the colony at this one site only. Strongly reinforcing the interpretation of a spill impact was the analysis of hopanoid petroleum biomarkers isolated from the floc collected from the impacted corals: comprehensive two-dimensional gas chromatography revealed a high degree of similarity with Macondo well oil (Boehm and Carragher, 2012). Some experts contend that these observed effects on the coral colony are due to nearby natural seeps or submarine landslides (Boehm and Carragher, 2012) rather than to the DWH oil spill, but the possibility of these alternatives is low, given the extensive surveys of the area in question (White et al., 2012).

Information indicating impacts on the large fauna on the extensive mud bottom are based on analysis of ROV video recordings (Valentine and Benfield, 2013). The bottom was surveyed at four locations north, south, east, and west 2,000 m from the DWH blowout preventer (BOP); a fifth site was 500 m north of the BOP. Faunal density, species richness, and species composition varied spatially in a manner consistent with impact at the 500-m site and at the western and southern 2,000-m sites. The conclusion that impacts had occurred was reinforced by observation of low numbers of apparently dead holothuroids and sea pens at those locations. Impact to mid-water zooplankton was indicated by the presence of dead pyrosomes and salps on the seafloor at all locations. Unlike the observations of impacted corals on deep hardgrounds (White et al., 2012), no collected specimens or sediments were taken for hydrocarbon analysis.

The reported impact on corals and soft-bottom biota are consistent with these observations. Effects might be sufficiently great so as to influence potential commercial upper-ocean pelagic species, which are somewhat dependent on the biomass aggregations of the deep-scattering layer and on the seafloor. Spill impact on the nonliving resources of the deep GoM may come through increased regulation and prohibitions intended to prevent environmental damage.

Finding 5.17. The generally low level of understanding about the deep GoM makes it very difficult to assess the full impact of the DWH oil spill on ecosystem services. There are few, if any, ways in which the spill will have altered the larger-scale physics of the deep GoM, leaving only the biological and biogeochemical processes subject to major effects. It is, however, possible to consider the likely impact scenarios on supporting, regulating, and provisioning services. The cultural impacts of the spill are more nebulous, but they include what might best be called a loss of wilderness.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

Baseline Data for the Deep GoM

The U.S. Department of the Interior has the authority to manage seafloor mineral resources in federal submerged lands to the extent of the EEZ. Since receiving the initial mandate, the required tasks have been carried out under different organizational arrangements, beginning with the Bureau of Land Management and then followed by the Minerals Management Service (MMS) and the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE). Following the DWH oil spill, BOEMRE was divided into the Bureau of Ocean Energy Management (BOEM) and the Bureau of Safety and Environmental Enforcement. The critical task of identifying information needed to ensure protection of the natural and human environment has been the primary responsibility of the Environmental Studies Program (ESP), which was initiated in 1973 (NRC, 1992) and is currently a component of BOEM. ESP has a headquarters division and regional programs in the GoM, the Pacific, and Alaska.7

ESP has a scientifically trained staff, but it lacks a dedicated research component and, in most instances, supports information gathering by means of the Department of Interior procurement authority, which includes competitive bidding, cooperative agreements, and memoranda of understanding. Contracts to carry out studies in deep water have traditionally gone to various combinations of academic institutions and the offshore service industry. Partnerships within government have made use of research platforms and staffs of NOAA and the Biological Resources Division of the U.S. Geological Survey.

As a result of the continuing efforts of ESP and its partners and contractors, the GoM is one of the most extensively studied regions of the world’s oceans on a relative basis (volumetrically, most of the global ocean remains unexplored). As will be discussed later, data gaps and inadequately addressed phenomena prevent the establishment of ecological production functions for the deep GoM. However, a basic of understanding of species inventory and the physical environment has been established for the continental shelf and the deep basin. Until the late 1980s, the primary sources of information about the deep GoM came from the sampling programs directed by Willis Pequegnat at Texas A&M University between 1964 and 1973 and were supported without regard to oil and gas development primarily by the U.S. Navy’s Office of Naval Research. With the intention to bring these results into the decision-making process for pioneering deep oil leases, BOEM supported an initial synthesis of results from 111 sampling stations above 1,000 m in the U.S. EEZ between Brownsville, Texas, and Desoto Canyon (Pequegnat et al., 1976). Subsequently, a Gulf-wide synthesis of 246 stations was supported (Pequegnat, 1983). The stations were sampled primarily for megafauna on the continental slope to a basin depth of 3,658 m. Extensive hardgrounds on the West Florida Escarpment and Yucatan Peninsula prevented investigation of these eastern and southeastern regions.

The Pequegnat et al. (1976) sampling efforts collected some hydrographic data, but it was primarily a zoogeographic study and biodiversity inventory. As such, it lacked the more comprehensive suite of measurements that became standard in BOEM-initiated baseline studies on the continental shelf. These more comprehensive investigations included the South

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7http://www.boem.gov/About-BOEM/BOEM-Regions/Index.aspx.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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Texas Outer Continental Shelf Study, the Mississippi Alabama Florida study, and the Southwest Florida Shelf study, which included sediment hydrocarbon and metal contaminant measurements along with biological surveys (Carney, 1995). These studies were ecologically comprehensive in that they examined both the seafloor (benthos) and water column (pelagos). A BOEM deep-sea baseline-type study was initiated and carried out on five cruises between 1983 and 1985. The primary results of the Northern Gulf of Mexico Continental Shelf Study (NGMCS) were presented in its third- and fourth-year annual reports (Gallaway, 1986, 1987). The sampling design was not hypothesis-driven in a formal sense; rather, it incorporated Pequegnat’s system of faunal zones and the need to compare eastern, central, and western planning regions. In addition to benthic fauna, alkanes were analyzed for indication of petroleum hydrocarbon, along with metals. Pelagic work was limited to water column hydrology and chemistry.

The 10 years following the completion of the NGMCS study saw the initiation of sufficient deep-oil drilling that a second comprehensive benthic study was initiated in 1999, the DGoMB project. Sampling was carried out between 2000 and 2002. Major results were published in a special volume of Deep-Sea Research (Rowe and Kennicutt, 2008) and a final report issued by Rowe and Kennicutt (2009).

Although lacking a substantial analysis of the water column, the DGoMB study is noteworthy with respect to future transition from habitat characterization to an ecosystem services approach. It included ecosystem function and model development in addition to the more traditional biological surveys. Sampling design was structured around specific hypotheses and included stations in close proximity to the DWH site. Primary productivity and carbon flux to the bottom, although not directly measured, were estimated from surface chlorophyll data. Benthic microorganisms were included as well as animal taxa.

BOEM has contracted three major studies of seep communities and has afforded this special habitat protection through issuance of a Notice to Lessees (BOEM, 2012; National Ocean Service, 2012). When protection of deep coral habitat became a major issue in the European Union, BOEM contracted a series of studies to map and assess similar systems in the GoM and elsewhere within the U.S. EEZ. The second large study of deep corals, “Lophelia II,” was under way at the time of the DWH blowout and was converted into an NRDA task.

Role of Industry in Baseline Development

People generally familiar with environmental permitting may assume that the offshore industry carries out substantial environmental surveys prior to any drilling activity. Were that the case, a baseline would have been determined for the thousands of wells already drilled. In fact, the Department of the Interior, in the role of manager of nationally owned offshore lands, carries out studies and prepares reports that meet National Environmental Policy Act requirements. The offshore industry has relatively minimal requirements to contribute to the overall understanding of the ecology of either the deep or shallow GoM. Much of the data developed by industry and submitted as a part of the permitting and planning process are proprietary and not available for review. The primary requirement in deep water is that the proposed drill-

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
×

ing must avoid sensitive habitats such as seep or hardgrounds. As evidence that such systems are being avoided, BOEM accepts geophysical or video recordings of the bottom taken by ROVs. The industry does from time to time exceed BOEM’s minimal baseline requirements. Any ecological data gathered, however, are considered proprietary or otherwise are not made available for independent scientific analysis.

A particularly noteworthy program in which industry makes a major contribution to data gathering and understanding of deep circulation is the BOEM Deepwater Current Monitoring on Floating Facilities program initiated in 2005. With few exceptions, floating facilities in water deeper than 400 m must acoustically monitor water movement through most of the water column. The data are publicly available online from the National Data Buoy Center (Bender and DiMarco, 2008).

The Heavily Studied But So-Poorly-Known Contradiction

Given that BOEM studies have provided so much information about the deep GoM, it is critically important to understand why the region has often been characterized as “poorly known” during and after the DWH spill. Beyond a lack of familiarity with GoM studies on the part of some spill responders, four causes can be suggested and corrected: (1) sparse data, (2) data less suited to serving as a baseline, (3) limited ability to access data collected over three decades, and (4) lack of conceptual frameworks that produce useful syntheses of existing data.

With respect to sparse data, a major challenge to managing the deep GoM or any other portion of the United States’ deep EEZ is the problem of obtaining adequate data density to support management decisions and to provide a baseline from which to assess any damage due to exploitation. The deep GoM is a very large area that must be sampled by very small devices for understanding ecology and ecosystem services. This is especially the case for biotic inventories, sediment analyses, and benthic metabolism. How little of the actual deep habitat is actually sampled can be seen from an examination of the two major biological surveys of the deep GoM bottom: the NGMCS study (Pequegnat et al., 1990) and the DGoMB study (Rowe and Kennicutt, 2008). In the relatively recent DGoMB study, the sedimentary biota was sampled with a corer 271 times for a total area sampled of only 46 m2 (Wei et al., 2010b). The older NGMCS study took 324 cores for similar analysis, but these were of a smaller size and the total area sampled was only about 20 m2. Thus the major portion of deep GoM sampling that has contributed to habitat classification and that might be used as a baseline for the deep sedimentary environment has covered a seafloor area of less than 70 m2. Given that the deep GoM is not a homogeneous region, it remains grossly undersampled. The deep water column biota has largely been ignored: there are few pre-spill data sets to either characterize the habitat or serve as a baseline.

With respect to collecting relevant data, management agencies such as BOEM are faced with the challenge of balancing regulatory obligations and limited budgets with evolving strategies of natural systems management and an incomplete understanding of what parts of natural systems are most important. Based on prior recommendations to increase data density

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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and gather data relevant to ecosystem functioning (NRC, 1992), it might be useful to assess the progress and limitations of deep GoM understanding of the past 20 years. As part of that assessment, the data requirements of the ecosystem services approach can be determined.

With respect to data access, all reports produced by ESP since its inception are available online at the Environmental Studies Program Information System.8 Studies completed prior to the use of digital media are available as scanned images. The lack of a central topic index and the lack of geospatial information other than regional seriously limit the utility of these reports. The extent to which the reports include the critically important raw and processed data is highly variable. BOEM partners with the National Oceanographic Data Center (NODC) of NOAA for data archival. Much oceanographic data collected before 1995, however, remain in the Multi-Discipline Archives Retrieval System format, which is no longer supported. In addition to ESP studies, BOEM obtains information about the deep environment from industry during the process of approving exploration and development plans. This information includes video surveys to determine if protected habitats are present and seismic data for multiple purposes. Although of considerable ecological relevance, these data are proprietary and unavailable for independent analysis.

Whether or not we can obtain and facilitate access to more data of greater relevance depends upon how the data are to be utilized. As more and more data are being collected, there is a growing need for an integrative process for search, retrieval, and analyses.

Finding 5.18. As discussed throughout this report, contemporary management of deep-sea resources will benefit from the adoption of new perspectives such as ecosystem-based management, ecosystem services approach, and management for resilience. For each of these perspectives, new ideas are being proposed and critically examined. Meshing this process of idea evaluation with appropriate and adequate field data is a critical activity that should engage the participation of the academic community, federal agencies, and the offshore industries.

BOEM’s deep-water program initiated a limited geospatial ecological synthesis effort in the form of Grid Programmatic Environmental Assessments (GPEAs). The deep GoM was divided initially into 17 and later 18 regions (Richardson et al., 2008). Depending primarily upon proprietary data submitted as part of exploration and development plans, BOEM would determine the adequacy of existing information. For example, DWH’s Mississippi Canyon lease block 252 is in grid cell 16. MMS issued an environmental assessment for this lease block in 2002 (MMS, 2002), indicating that the data were judged to be adequate—a conclusion that might profitably be reexamined in light of events. The effectiveness of GPEA executions prior to the DWH oil spill can be argued, but with more careful examination of criteria and with all data available and accessible, a similar approach may be useful going forward.

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8http://www.data.boem.gov/homepg/data_center/other/espis/espismaster.asp?appid=1.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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Deep-Sea GoM Conclusions

The DWH oil spill occurred within the deep habitats of the GoM, producing a sustained buoyant plume that rose to the surface, crossing the density gradient (pycnocline) and contaminating both the slowly mixed lower and more rapidly mixed upper water column. In addition, nonbuoyant plumes remained in the lower volume, contaminating water and bottom areas as these plumes intersected the continental slope. The environmental impacts of these contaminations are being investigated as part of the NRDA process, but few results had been released at the time of this writing. That work requires the time-consuming processing of samples of small fauna. In the case of deep corals that are more easily observed in the field, however, areas of injury consistent with exposure to deep plumes have been documented. Because of the increasing exploitation of deep-water areas, including the GoM, deep habitats will be increasingly at risk.

With respect to the deep-sea environment of the GoM, an ecosystem services approach affords the potential to greatly improve the effectiveness of environmental management, especially as the ecosystem services approach is refined to better consider the ecological functions of this very large but poorly understood system. In addition, this approach is directed at an understanding of ecosystem interactions rather than the promotion of species inventory and habitat classification. It is likely that microbial and faunal contributions to hydrocarbon attenuation, carbon sequestration, and nutrient recycling are critical ecosystem services that may require careful management. Actual assessment of ecosystem services and their distribution across the deep GoM will, however, require substantial innovation both conceptually and technologically. Work needs to be done from a thoughtfully developed conceptual base, guiding careful sampling, with access to integrative tools for analysis and synthesis.

Of the ecosystem services considered, the linked biological, geochemical, geological, and physical systems of the GoM interact to provide critical supporting and regulating services. The exact nature, rates, and distribution of the interactions and resulting services present many critical questions. How does the complex circulation across two sills and the Caribbean prevent deep hypoxia within the GoM basin under normal and spill-impacted conditions? How does the complex deep circulation interact with the Loop Current to determine the distribution of recycled nutrients within the GoM and the larger Atlantic? From a comprehensive perspective, what is the carbon balance of the GoM: is the deep a net sink or a net source?

Of very special interest is the ability of the microbial system, closely linked to the physical system, to consume naturally seeping liquid and gas hydrocarbons. How does this attenuation capacity vary within the GoM, as well as other regions of the global ocean? How does it impact nutrient and gas balance in slowly mixed deep water? Can this capacity be decreased by industrial accidents or other mismanagement? Through the development of broad-based knowledge of the ecosystem dynamics of the deep GoM, required for an ecosystem services approach, we can hope to answer many of these fundamental questions.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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SUMMARY

The four case studies presented in this chapter (wetlands, fisheries, marine mammals, and the deep sea) were chosen to provide examples of how an ecosystem services approach may be applied to assess the impact of the DWH oil spill on several key ecosystem services in the GoM. They represent a range of conditions with respect to the amount and utility of available data, our fundamental understanding of the functioning of the ecosystem subcomponents, the values of the services in market and nonmarket terms, and the range of the impacts of the spill on the services. As such, they serve as exemplars of how an ecosystem services approach can add to the ability to capture the full impact of an event such as the DWH oil spill and, at the same time, illustrate the challenges faced when attempting this approach.

The case studies should make it clear that, within the GoM, some ecosystem services (e.g., storm mitigation from wetlands) are associated with years of research and baseline measurements, which creates a situation in which adequate ecological production functions and valuation processes exist to carry out an ecosystem services approach to damage assessment, with a high likelihood that the result will provide a more holistic view of the impact of the DWH oil spill and a wider range of restoration options. In the case of the ecosystem services provided by fisheries, valuation techniques are well established (at least for the provisional services) and a significant amount of baseline data exist, but these data suffer from a lack of spatial specificity, which affects the ability to assess impacts on the current and future productivity of the fisheries. The final two examples (marine mammals and the deep GoM) highlight the difficulties in estimating the full range of impacts when the current database, level of understanding of ecosystem interactions, and approaches to valuation are clearly inadequate. Nonetheless, in each case, the potential benefits of an ecosystem services approach are outlined. The next chapter discusses the research efforts that are needed to realize these benefits.

Suggested Citation:"5 Ecosystem Services in the Gulf of Mexico." National Research Council. 2013. An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico. Washington, DC: The National Academies Press. doi: 10.17226/18387.
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An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico Get This Book
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As the Gulf of Mexico recovers from the Deepwater Horizon oil spill, natural resource managers face the challenge of understanding the impacts of the spill and setting priorities for restoration work. The full value of losses resulting from the spill cannot be captured, however, without consideration of changes in ecosystem services--the benefits delivered to society through natural processes.

An Ecosystem Services Approach to Assessing the Impacts of the Deepwater Horizon Oil Spill in the Gulf of Mexico discusses the benefits and challenges associated with using an ecosystem services approach to damage assessment, describing potential impacts of response technologies, exploring the role of resilience, and offering suggestions for areas of future research. This report illustrates how this approach might be applied to coastal wetlands, fisheries, marine mammals, and the deep sea -- each of which provide key ecosystem services in the Gulf -- and identifies substantial differences among these case studies. The report also discusses the suite of technologies used in the spill response, including burning, skimming, and chemical dispersants, and their possible long-term impacts on ecosystem services.

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