Lozano, S. J. US EPA Mid-Continent Ecology Division, lozano.stephen@epa.gov
Nalepa, T. J. NOAA/Great Lakes Environmental Research Laboratory, nalepa@glerl.noaa.gov

 
CHANGES IN THE FRESHWATER BENTHIC COMMUNITY OF LAKE ONTARIO SINCE THE INVASION OF DREISSENA: 1972-1997
 
Population changes of three major benthic taxa are discussed in relation to Dreissena spp. Lake Ontario was sampled pre-invasion (1972) and post-invasion (1994, 1997) for abundance of benthic organisms. In offshore sediments of Lake Ontario, neither species composition nor abundance of important benthic organisms changed. In the nearshore sediments after 1994, there was a marked decline in mean density of Diporeia, Oligochaeta and Sphaeriidae and increase of Dreissena, especially in the 10-80 m zone along the U.S. shoreline and in the Kingston basin where Diporeia abundance fell to zero where previous levels were as high as 14,000 square meter. The loss of Diporeia coincided with an increase in water clarity and a decrease in primary production. Diporeia accounts for a major portion of benthic invertebrate biomass in Lake Ontario and provides a major link between prey fish and primary production. The decline of Diporeia from the nearshore waters of Lake Ontario coincided with the decline of demersal and pelagic prey and sport fish populations. The timing of spring diatom blooms and formation of thermal bars plays an important regulating role in the spatial extent of the Dreissena filtering effects on the Lake Ontario ecosystem.
 
Day: Wednesday, Feb. 3
Time: 02:00 - 02:15pm
Location: Eldorado Hotel
 
Code: SS18WE0200E