444 



Nnn-uative Species — Our Living Resources 



For further information: 



Thomas A. Edsall 



National Biological Service 



Great Lakes Science Center 



1451 Green Rd. 



Ann Arbor, Ml 4S1U5 



and 1970"s. A second pathogen, bacterial kid- 

 ney disease, has been implicated in the massive 

 moilalities of Pacific salmon in Lake Michigan 

 in recent years (MDNR 1992). Two other intro- 

 duced pathogens cause salmon whirling disease 

 and furunculosis. but they occur mainly in fish 

 hatcheries where crowding makes fish vulnera- 

 ble to outbreaks of disease. 



The anival of the zebra mussel (Dreissemi 

 polymorpha) in Lake Erie in 1986 (Leach 1992) 

 set the stage for long-term changes in pelagic 

 and benthic comiiiunilies in the Great Lakes and 

 in the economic and social future of lake users. 

 The zebra mussel may cause substantial 

 changes in the food chain, resulting in a proba- 

 ble reduction in the overall production offish in 

 the Great Lakes. Zebra mussels also foul private 

 vessels and structures, and nautical and littoral 

 structures, including water intakes, in the Great 

 Lakes. The zebra mussel has spread to southern 

 Ontario in Canada; its westward range exten- 

 sion includes the Mississippi River and some of 

 its tributaries from the river's headwaters near 

 St. Paul. Minnesota, to its mouth at New 

 Orleans, Louisiana. Negative ecological, eco- 

 nomic, and societal effects are expected from 

 these and future range expansions. 



Introduced plant species outnumber all other 

 groups of introduced organisms, but the effects 

 of only a few of these are known. Purple looses- 

 trife has spread throughout the Great Lakes 

 basin and is replacing the cattail (Typha lati- 

 folia) and other wetland native plants. Purple 

 loosestrife has no food value for wildlife and is 

 making wetlands less suitable as wildlife habi- 

 tat. Eurasian watermilfoil has also had a sub- 

 stantial effect in lakes in the Great Lakes basin. 

 Massive beds of the plant often make boating 

 and swimming impossible and reduce fish and 

 invertebrate populations. Some introduced 

 species of algae have become dominant mem- 

 bers of the algal community of the Great Lakes. 

 Their ecological impacts are generally 

 unknown, but one. Stepluinodisciis hiiulemniis, 

 has caused water-quality problems on several 

 occasions. 



The ecological effects of the introduced 

 crustaceans, oligochaetes, bryozoans, cnidari- 

 ans, and tlatworms are largely unknown. 



Historically, the ecological and economic risks 

 associated with these groups have not been as 

 high as those posed by other plants and animals. 

 The recently introduced spiny water flea 

 (.Bythotrephcs cederstroemi). a predatory zoo- 

 plankter, has rapidly expanded in the Great 

 Lakes. Its ecological effect is unknown, but its 

 establishment in Lake Michigan coincided with 

 observed changes in the zooplankton communi- 

 ty characteiistic of those caused by an inverte- 

 brate predator. 



Conclusions 



The ecological, social, and economic effects 

 of exotic species in the Great Lakes continue to 

 be enormous. Serious effects have been docu- 

 mented for only a fraction of the species intro- 

 duced into the Great Lakes. However, most 

 introduced species have not been thoroughly 

 studied to detemiine their effects on the ecosys- 

 tem. Introduced species exist at almost every 

 level in the food chain, and their effects must 

 certainly pervade the entire aquatic community 

 of the Great Lakes. We believe that as long as 

 human-mediated transfer inechanisms persist 

 and habitat alterations that stress native aquatic 

 communities are allowed to occur, the Great 

 Lakes ecosystem will also be at substantial risk 

 from new, undesirable, exotic species. 



References 



Edsall. T.A.. J.H. Selgeby. T.J. DeSorcie. and J.R.P. French 

 III. 199,1. Growth-temperature relation for young-of-the- 

 year ruffe. Journal of Great Lakes Res. 19:630-633. 



GLFC. 1992. Ruffe in the Great Lakes: a threat to North 

 Amencan fisheries. Great Lakes Fishery Commission, 

 Ann Arhor. MI. 144 pp. 



Leach. J.H. 1992. Impacts of zebra mussels {Dreissemi 

 polymorplui) on water quality and tlsh spawning reefs in 

 western Lake Erie. Pages 381-397 in T.F. Nalepa and 

 D.W. Schloesser. eds. Zebra mussels: biology, impacts, 

 and control. CRC Press. Boca Raton. FL. 



MDNR. 1992. Dingell-Johnson Annual Report. Project F- 

 53-R-8. Study 471-2. Michigan Department of Natural 

 Resources. Lansing. 10 pp. 



Mills. E.L.. J.H. Leach. J.T Carlton, and C.L. Secor. 1993. 

 Exotic species in the Great Lakes: a history of biotic 

 crises and anthropogenic introductions. Journal of Great 

 Lakes Res. 19:1-54." 



