. Benthic macroinvertebrate communities in southwestern Lake Ontario following invasion of Dreissena and Echinogammarus: 1983-2000.

Abstract

Benthic macroinvertebrate communities were quantified at natural cobble and artificial reef sites in Lake Ontario in 1983 (7 y pre-Dreissena invasion) and in 1991-1992 and 1999-2000 (1-2 and 9-10 y post-Dreissena invasion, respectively). Overall, the natural cobble community had higher species diversity and community abundance than the artificial reef community. While taxonomic composition of both communities remained consistent during the study period, organism abundance (excluding Dreissena) increased sharply from 1983 to 1991-1992, and that all taxa declined to 1983 levels by 1999-2000. From 1991-1992 to 1999-2000, Dreissena bugensis, which mostly replaced D. polymorpha, and Echinogammarus ischnus (all invasive species) appeared in the studied community. We conclude that the transition from D. polymorpha to D. bugensis and processes associated with the ongoing oligotrophication of Lake Ontario are responsible for the reduced density of large-bodied Dreissena in the nearshore region of the lake, and that changes in the Dreissena population are largely responsible for changes in the non-Dreissena benthic macroinvertebrate community.