Benthic Macroinvertebrate Communities in Southwestern Lake Ontario Following Invasion of Dreissena: Continuing Change

Abstract

Benthic macroinvertebrate communities were compared and quantified at natural cobble and artificial reef sites in Lake Ontario in 1983 (pre0-Dreissena invasion), and in both 1991-1992 and 1995 (1 to 2 and 5 years post-Dreissena invasion, respectively). Diversity and abundance of non-dreissenid macroinvertebrates generally rose from 1983 to 1991-1992, but returned to 1983 levels or lower by 1995. Although community similarity (excluding Dreissena from analysis) remained high across study years, the 1995 invertebrate community more closely resembled the pre-Dreissena community of pre-1983 than the initial post-Dreissena community of 1991-1992 because of recent declines in the absolute abundance and diversity of macroinvertebrates. In particular, gastropods responded negatively to Dreissena or to associated benthic habitat or community changes that occurred from 1991-1992 to 1995. These results suggest that short- and long-term effects of Dreissena on other organisms may be quite different, and illustrate the need for long-term monitoring of biological communities in order to more fully determine effects of invasive species or other environmental perturbations on ecosystems.