Effects of an exotic bivalve mollusc on benthic invertebrates and food quality in the Ohio River

Effects of zebra mussels (Dreissena polymorpha) on populations of amphipods (Gammarus fasciatus) and proso-branch snails (Lithasia obovata) and on nutritional quality of benthic organic matter were examined in 20 artificial streams receiving Ohio River water and containing either mussels or small gravel. Twenty individually-marked snails were placed in each trough, and streams were allowed to colonize with other benthic species for 28 days. Dreissenids positively affected other benthic invertebrates in our stream channels. Compared to gravel channels, Gammarus biomass was significantly higher (P < 0.01) in mussel channels, amphipod densities increased similar to 300%, and snail growth rates were similar to 50% greater. Food quality of fine benthic organic matter (FBOM) was greater in mussel channels (i.e. lower C:N), and FBOM was carbon depleted (lower delta C-13) but nitrogen enriched (higher delta N-15). Isotope data suggest that detrital FBOM was not the sole food source for snails and amphipods in our channels and that they were assimilating a higher quality portion of this BOM. The overall influence of dreissenids on particular benthic invertebrates may depend on the response and/or susceptibility of those species to biofouling, increased habitat heterogeneity, and changes in the quality and quantity of nutrients.