Suspension-feeders and coexisting infauna: an enhancement counterexample

Mytilus edulis L. density was manipulated in a New England soft-bottom intertidal population, and the response of the oligochaete Tubificoides benedeni (Udekem) was measured to test the hypothesis that the presence of mussels causes increased oligochaete abundance. There was a positive correlation between mussel density and oligochaete abundance within the mussel bed, and removal of mussels from 1-m 2 patches led to a 50% decline in oligochaetes after 3 months. These results support the proposed hypothesis and contradict the idea that no infaunal forms should attain their highest densities among densely packed suspension-feeding bivalves. T. benedeni juveniles emerge from cocoons and may escape ingestion by M. edulis and suffocation in mussel feces and pseudofeces. In benthic environments where suspension-feeders reduce successful planktonic larval settlement, we suggest that those infauna which form cocoons, brood, fragment asexually, or disperse at large postlarval stages may be relatively more abundant than species with planktonic larval dispersal.