Changes to the deepwater benthos of eastern Lake Erie since the invasion of Dreissena: 1979-1993

The deepwater benthic community in Lake Erie was resampled in 1993, using the same sites and methods as used in a 1979 survey (before establishment of Dreissena bugensis). This exotic mussel was present at all 13 sites in 1993 (shells >2 mm long, averaged 3240.m(-2)) and formed over 91% of the benthic biomass beyond 30 m depth. Total dry biomass (shell-free) increased from 1.58 g.m(-2) in 1979 to 11.93 g.m(-2) in 1993. The burrowing amphipod Diporeia hoyi declined from 38 to 1.8% of the total benthic biomass from 1979 to 1993, and its density declined from 1840.m(-2) in 1979 to 220.m(-2) in 1993. Diporeia hoyi was common at all sites in 1979, but absent at eight sites and common at only two sites in 1993. Likewise, reductions in native clams (Pisidium spp.) (from 330 to 80.m(-2)) may be due to competition with mussels for freshly settling algae. No significant reduction was measured for oligochaetes or chironomids. Excluding Dreissena, the total macro- and meio-fauna increased from 20 100 to 48 400 organisms m(-2), but total biomass decreased from 1.58 to 0.98 g.m(-2). The meiofauna (small nematodes, ostracods, and harpacticoids) increased in density, perhaps benefiting from the deposited pseudofeces of the mussels.