Great Lakes Shipping, Trade, and Aquatic Invasive Species Special Report 291 (2008) / Chapter Skim
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3 Aquatic Invasive Species in the Great Lakes
3 Aquatic Invasive Species in the Great Lakes
Pages 43-62
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From page 43... ...
Historical trends in AIS introductions are important in assessing the effectiveness of measures taken to prevent such introductions, and the challenges in interpreting observed trends are examined. Brief remarks about future AIS introductions are made, and the chapter concludes with a summary of key points pertaining to the committee's task.
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From page 44... ...
The origins are less certain for invasive plants that now dominate coastal wetlands in highly urbanized areas, such as Lake Michigan's lower Green Bay. INVASION VECTORS AND PATHWAYS In invasion biology, a vector is defined as the physical means or agent by which a species is transported.
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From page 45... ...
and not terrestrial invasive species. Most AIS that have drawn attention in recent decades inhabit benthic or pelagic areas of the Great Lakes, although the system has been invaded by and remains vulnerable to invasions by wetland species such as hybrid cattail (Typha x glauca)
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From page 46... ...
Hull Fouling Vector Ballast water, as well as residual ballast water and sediment, has been well characterized for transoceanic vessels entering the Great Lakes.2 In contrast, there is a dearth of information with regard to the risk of AIS introductions posed by hull fouling on such vessels. Marine-to-marine introductions on hulls of ships have occurred for hundreds of years, and studies conducted in marine 1 The analysis showed Europe to be the source of 94 percent of ballast-mediated invasions, includ ing 15 species from western and central Europe, 12 from the Ponto-Caspian region, and three from the Baltic Sea.
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From page 47... ...
of vessels entering the Great Lakes will be needed to help determine whether hull fouling is an important mechanism for AIS introductions. Absent a solid body of evidence indicating the importance of the hull fouling vector, the committee's analysis of options for preventing further introductions of AIS by vessels transiting the St.
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From page 48... ...
In addition, invasive plants in Great Lakes coastal wetlands, such as Typha and Phalaris arundinacea, have resulted in the exclusion of many native species and declines in plant species richness and evenness of distribution. The following section summarizes the impacts of one of the Great Lakes' highest-profile invaders -- the zebra mussel.
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From page 49... ...
As suspension feeders, zebra mussels bio-accumulate metals and organic contaminants, and the transfer of these contaminants up the food chain to waterfowl and fish that eat mussels has the potential to change contaminant cycling in the system significantly (see, for example, Mazak et al.
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From page 50... ...
Less Studied AIS While invaders such as the zebra mussel are unlikely to go unnoticed because of their abundance, size, and readily observable and widespread impacts, the same cannot be said of all AIS. For example, analyses of beach sand revealed introduced species of benthic copepods and testate rhizopods, species that are both inconspicuous and low impact (Horvath et al.
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From page 51... ...
Moreover, some researchers have questioned whether free-living microorganisms should be designated as invasive species at all, arguing that these species are found everywhere and that their distribution is not specific to certain geographical areas (Finlay 2002) .6, 7 Other researchers 6 This argument applies only to free-living microorganisms.
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From page 52... ...
In light of this ongoing debate and the numerous unknowns and uncertainties with regard to the appearance of VHS in fish populations in the Great Lakes, it remains unclear whether ships' ballast water played any role in the recent VHS outbreak. However, in view of the natural abundance and widespread distribution of aquatic microorganisms, the committee sees merit in the approach taken by the International Maritime Organization, which differentiates microorganisms from other AIS in its proposed ballast water performance standard (IMO 2004)
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From page 53... ...
2006) , commercial aquaculture operations, and the ballast water of vessels entering the Great Lakes from marine waters in eastern North Americaa (see, for example, (continued)
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From page 54... ...
National Park Service closed Lake Superior waters within the boundaries of Isle Royale National Park to the release of untreated ballast water (Lake Carriers' Association 2007; Lake Superior Magazine 2007)
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From page 55... ...
. Alternatively, a small population could persist undetected at a relatively low level for a considerable period of time until the emergence of a superbly adapted local genetic variant results in the establishment of a detectable population.11 The nature of the time lag for any particular species influences the pattern of cumulative numbers of invasions over time.
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From page 56... ...
FUTURE AIS INTRODUCTIONS The vectors and pathways by which AIS enter the Great Lakes are continuously changing. In the case of the shipping vector through the seaway, for example, changing trade patterns and routes may provide opportunities for AIS from new donor areas to enter the Great Lakes or open up alternative pathways for AIS from known donor areas.
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From page 57... ...
The following paragraphs provide a brief overview of approaches to identifying "hot species, hot spots, and hot moments" for future AIS introductions and note some possible effects of climate change on AIS introductions into the Great Lakes. Hot Species, Hot Spots, and Hot Moments A paper commissioned by the committee in support of its work notes that there have been a number of recent efforts to identify new AIS most likely to establish populations in the Great Lakes ("hot species")
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From page 58... ...
Current evidence indicates that the hull fouling vector has played a very minor role in introducing AIS into the freshwater ecosystem of the Great Lakes. Eliminating AIS introductions by vessels transiting the seaway would have an important impact on the AIS problem in the Great Lakes but would not eliminate all further AIS introductions.
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From page 59... ...
Thus, adaptive elimination strategies will likely be needed to respond to the ever-changing threat of AIS introductions. REFERENCES Abbreviations IMO International Maritime Organization NRC National Research Council Dobbs, F
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From page 60... ...
2007. Isle Royale National Park Prohibits Untreated Ballast Water Release.
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From page 61... ...
2005. The Economic Impacts of Aquatic Invasive Species: A Review of the Literature.
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From page 62... ...
2007. Surveillance and Control of Aquatic Invasive Species in the Great Lakes.
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