A field experiment to determine Dreissena and predator effects on zoobenthos in a nearshore, rocky habitat of western Lake Erie

Results from several previous studies showed that zebra and quagga mussels (Dreissena polymorpha and D. bugensis, respectively) are key structuring ag ents of benthic invertebrate communities. However, the relative effects of Dreissena and other potentially important biotic factors on these communiti es remain poorly understood. The goal of this study was to improve our unde rstanding of community-structuring mechanisms in habitats with Dreissena by quantifying simultaneous effects of Dreissena and large benthic predators (primarily fish) on invertebrates inhabiting hard substrates in western Lak e Erie Biomass, densities, and diversity of invertebrates were compared on bricks with low and high (= ambient) Dreissena biomass that were held in we stern Lake Erie for 49 d within cages that excluded large predators, partia l cages where predators had access to invertebrates, and cageless-reference plots. Dreissena had positive effects on total invertebrate biomass, and b iomass of gastropods, chironomid larvae, and the amphipod Echinogammarus is chnus. Dreissena also caused increases in taxonomic richness of invertebrat es, Echinogammarus body size, and densities of several invertebrate taxa. O ur results suggest that predators reduced Echinogammarus biomass in the hig h Dreissena biomass treatment. However, predators did not affect Dreissena biomass, total invertebrate biomass, invertebrate densities, or taxonomic r ichness of invertebrates. We conclude that both Dreissena and large predato rs regulate invertebrate community structure on hard substrates in western Lake Erie, but that Dreissena are of much greater importance.