104 



lems associated with introductions of non-indigenous species. The Task Force has 

 made an effort to fulfill its responsibilities under the Act despite having less funding 

 available than authorized. 



Much of the impetus for the Act was the result of concern over the catastrophic 

 introduction of zebra mussels into the Great Lakes, and a major portion of the Fed- 

 eral effort has focussed on addressing this problem. 



In the marine environment, we are unable to point to major catastrophes caused 

 by species introductions as catastrophic as the introduction of the zebra mussel into 

 the Great Lakes. There are two reasons for this. First, as the Office of Technology 

 (OTA) report pointed out, some ecosystems are particularly vulnerable to species in- 

 vasions. Marine environments may be relatively less vulnerable to catastrophic in- 

 vasions. Second, we may simply be unaware of major marine introductions because 

 we still know less about marine ecosystems than terrestrial or freshwater 

 ecosystems. 



Nevertheless, there are examples of species introductions into marine environ- 

 ments that have had negative impacts. In April 1993, NOAA sponsored an inter- 

 national workshop on Non-indigenous Estuarine and Marine Organisms. Partici- 

 pants in the Workshop concluded that while we were not aware of a catastrophic 

 mtroduction of zebra mussels that had occurred in the marine environment, such 

 an occurrence is almost inevitable in the future. Participants also discussed past 

 problems associated with introductions. 



Whenever they occur, there are a number of potential risks associated with both 

 unintentional and intentional introductions. An introduced species may cause the 

 decline of native species in a number of different ways. Indigenous species may be 

 affected by direct predation, competition for key habitat or other resources, or hy- 

 bridization. Serious pathogens or parasites also may accompany a species when it 

 is introduced. 



Although there has been a tendency to focus on fish and shellfish introductions, 

 species that can be nuisances may include plants, single celled organisms, inverte- 

 brates, pathogens, and parasites. 



Off the east coast the introduced green alga, Codium fragile, was first considered 

 to be a nuisance in the area of Long Island m the early 1970s. The species has now 

 spread as far south as South Carolina, and there is concern that if it spreads far- 

 ther, it could affect coral reefs by blocking the sunlight on which they are depend- 

 ent. The saltmarsh cordgrass, Spartina atterniflora, is used for shoreline stabiliza- 

 tion on the east coast. Ebwever, it has had negative impacts after being introduced 

 to the west coast. It aggressively invades intertidal oyster habitat and can reduce 

 oyster productivity. Spsuiiina traps sediments and can transform low mudflats to 

 higher islands and may adversely affect Dungeness crab larvae that rely on mud 

 flat habitat. 



San Francisco Bay and the delta region feeding into the bay provide examples of 

 two other types of organisms that can have negative impacts. The Asian clam 

 Potamocorbula amurensis has colonized the bay and has been found in densities of 

 more than 20,000 per square meter. Several introduced copepods have displaced the 

 native copepod Eurytemora affinis which is a preferred prey species for a number 

 of larval fish. Alterations in prey base may have affected striped bass and other fish 

 production in the delta area. 



Even if a species itself is not a nuisance, it may introduce pathogens and para- 

 sites. Although of uncertain origin, one only needs to consider the impact of MSX 

 and dermocystidium on oyster production in the Chesapeake Bay to see the poten- 

 tial problem. Pathogens have had a serious impact on a number of economically im- 

 portant species. In addition to oysters and clams, other pathogens have been trans- 

 ferred with salmon and shrimp. The State of Hawaii has among the most stringent 

 screening requirements for diseases. This occurred because the introduced shrimp 

 virus IHHNV was responsible for major losses in the aquaculture industry. Even in- 

 troductions that have, on the whole, been beneficial have been accompanied by para- 

 sites. A significant portion of U.S. oyster production is dependent on the Japanese 

 oyster Crassostrea gigas that was introduced to the west coast. A number of species 

 were accidentally introduced with the oyster. One, the Manila clam, has itself be- 

 come a significant commercial species. However, two parasites — the Japanese oyster 

 drill and the oyster flatworm became established as a result of the oyster introduc- 

 tion. 



In Hawaii, a marine fish introduction may have led to the decline of a native spe- 

 cies. Near Oahu, the introduced Marquesan mullet has displaced the native mullet 

 for which a valuable fishery exists. 



The United States is not only a recipient of aquatic nuisance species. There are 

 examples of species from our waters that have impacted other ecosystems. The 

 Black Sea has been invaded by comb jellies from our waters. Comb jellies prey on 



