U.S. Department of Commerce


Date of this Version



Can. J. Fish. Aquat. Sci. 58: 518–529 (2001). DOI: 10.1139/cjfas-58-3-518


Surveys of benthic macroinvertebrates conducted in Lake Ontario during 1994 and 1997 revealed recent declines in populations of three major taxonomic groups: Oligochaeta, Sphaeriidae, and Diporeia spp. (Amphipoda), with the most drastic reductions occurring in the latter. Results from sediment measurements were used to classify deepwater sediments into three habitat zones. Densities of all three taxa declined in the shallowest (12–88 m) of the sediment zones between 1994 and 1997; the greatest changes in density were observed for Diporeia, which declined from 3011 to 145 individuals·m–2, and for total benthic macroinvertebrates, which declined from 5831 to 1376 individuals·m–2. Mean densities of Dreissena spp. in 1997 were highest in the shallowest zone, and the areas of greatest densities corresponded to areas of largest reductions in Diporeia populations. We believe that dreissenids are competing with Diporeia by intercepting the supply of fresh algae essential for Diporeia survival. A decline in macroinvertebrate densities, especially populations of an important food item such as Diporeia, in Lake Ontario sediments at depths of 12–88 m may have a detrimental impact on the benthic food web.