| Contents Notes |
Dramatic declines of the amphipod Diporeia (Pontoporeiidae) occurred in the Great Lakes after the arrival of Dreissena in the early 1990s. To investigate if declines were occurring elsewhere, densities in 2001-2003 were compared to historical data from 14 smaller regional lakes in Quebec, New York State, Ontario, and Manitoba. In four of the lakes, density of other invertebrates was also examined to determine if there were historical trends in other taxa. Of the five lakes that had Dreissena; only Lake Champlain yielded no Diporeia, densities in South Bay (Georgian Bay) decreased, yet in Cayuga and Seneca Lakes where Dreissena polymorpha or D. bugensis have been abundant for 10 years, Diporeia still remained plentiful. Seven of the nine lakes classified as lakes without mussels, including eutrophic Lake Winnipeg, maintained abundant populations of Diporeia, the remaining two lakes had densities lower than historical values. There was no evidence of a regional decrease, however statistically the presence of Dreissena reduced Diporeia populations in the data set examined |
