Assessing the Relationship Between Propagule Pressure and Invasion Risk in Ballast Water (2011) / Chapter Skim
Currently Skimming:
6 The Path Forward
6 The Path Forward
Pages 122-136
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 122... ...
. The key issue, however, is the ability to characterize quantitatively the risk–release relationship, with the goal of functionally describing the incremental reduction in invasion probability achieved with declining propagule supply.
|
From page 123... ...
. Such variation has important implications for establishing discharge standards, in that invasion probability is obviously context dependent, with many potential influences beyond simply the number of propagules delivered.
|
From page 124... ...
Current molecular tools can permit identification of many but not all species, but these tools have largely been developed since most of the intensive ballast water sampling was conducted in the U.S., and even with genetic techniques quantitative estimates may still be a challenge. Thus, estimates for historical propagule supply from ballast can at best provide a temporal snapshot of concentrations of total organisms and selected taxa at only a few ports.
|
From page 125... ...
In the case of ballast-mediated invasions, several studies have used the number of ship arrivals as a proxy for propagule supply. Even if a relationship is found between vessel arrivals and invasions (in space or time)
|
From page 126... ...
. Clearly, there is potential value in using proxy variables to characterize propagule supply associated with ballast discharge.
|
From page 127... ...
A well-designed ship discharge sampling program to measure propagule supply involves stratified random samples across ship type, source regions, and season that is repeated across years. For each ship sampled, the goal would be to characterize the abundance of individual species or taxonomic group of inter
|
From page 128... ...
Because concentrations of coastal plankton are expected to decrease through time with increasingly stringent ballast management, it is important to consider the effects of temporal changes in evaluation of propagule supply. In parallel to ballast water analyses, standardized field surveys are needed for the same estuaries, repeated over time, to estimate the occurrence of new invasions for the same taxa or species found in arriving ballast.
|
From page 129... ...
For example, the relatively large surface-to-volume ratio in mesocosms may influence plankton behavior and survival in ways not found in nature; the larger the mesocosm, the more one can reduce artifacts associated with walls and differential light penetration and the lower the propagule density of the inoculum that one can achieve, thereby providing greater reality to ballast discharges. In addition, it is not known a priori which species or taxonomic groups are most representative for examining invasion dynamics (i.e., the risk–release relationship)
|
From page 130... ...
when actual ballast volume data are available, these do not translate well into known propagule supply, such as species richness or abundance, and, further, (c) there is no significant relationship between ballast volume and invasions.
|
From page 131... ...
Indeed, using multiple models with the same data could be valuable to test for concordance. This would also allow one to assess the range of outcomes that would result from proposed ballast water discharge standards.
|
From page 132... ...
, chosen to include different coasts, ship traffic patterns, source regions, and environmental conditions. For each sentinel estuary, measures of propagule supply (in ships' ballast)
|
From page 133... ...
While collection of field-based descriptive data required for a meaningful analysis of the risk–release relationship is somewhat daunting in scope, recent developments make this more feasible than in the past, with continuing rapid improvements in the sensitivity and efficiency of analytical methods. First, pending international and national regulations require commercial vessels to install sampling ports that provide representative and standardized samples of ballast discharge (see Chapter 2)
|
From page 134... ...
* To date, there has been no concerted effort to collect and integrate the data necessary to provide a robust analysis of the risk–release relationship needed to evaluate invasion probability associated with particular ballast water discharge standards.
|
From page 135... ...
Nonindigenous Aquatic Spe cies in a United States Estuary: A Case Study of the Biological Invasions of the San Francisco Bay and Delta. A Report for the United States Fish and Wildlife Service, Washington, DC, and The National Sea Grant College Program, Connecticut Sea Grant, NTIS Report Number PB96-166525.
|
From page 136... ...
in reducing aquatic nonindigenous species (ANS) introductions to the Great Lakes Basin and Chesapeake Bay, USA: Synthesis and analysis of existing information.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.