Macroinvertebrate communities on hard substrates in western Lake Erie: Structuring effects of Dreissena

Of the approximately 140 non-indigenous species that have invaded the Great Lakes since the early 1800s, few have had greater effects on this ecosyste m than the zebra and quagga mussel (Dreissena polymorpha and D. bugensis, r espectively). In this study the effects of these bivalves on macroinvertebr ates inhabiting hard substrates in western Lake Erie were quantified. Bioma ss, densities, diversity of macroinvertebrates, and particulate organic mat ter mass were measured on bricks with high and low Dreissena densities that were held at a depth of 3.5 m for 49 days in 1996. Total macroinvertebrate densities and biomass (excluding Dreissena) were two and five times greate r on substrates with high Dreissena densities than when Dreissena were rare . These differences were largely attributed to the amphipod Echinogammarus ischnus, itself an invading species, which constituted 29 and 31% of total macroinvertebrate densities and biomass, respectively, on Dreissena-dominat ed substrates. Dreissena also stimulated increased macroinvertebrate divers ity, causing a shift from a community dominated by the chironomid Dicrotend ipes neomodestus to an assemblage characterized by increased densities and equitability of hydroids (Hydridae), the flatworm Dugesia tigrina, tubifici d oligochaetes, leeches (Alboglossiphonia heteroclita and immature Erpobdel lidae), limpets (Ancylidae), snails (Physella integra and Amnicola limosa), Echinogammarus, the microcaddisfly Hydroptila ?waubesiana, and the chirono mid Micro tendipes pedellus. No taxon responded negatively to Dreissena in this study. In addition, particulate organic matter mass, an important food and habitat resource for benthic invertebrates, was two times greater on D reissena-dominated substrates than on bricks with few Dreissena. Our result s support hypotheses that Dreissena have strong effects on community dynami cs and energy flow pathways in the Great Lakes.