Potential impact of two invasive species on the macroinvertebrate communities surrounding islands in navigation pools of the upper Mississippi River

Relatively little is known about the structure of near-shore, aquatic macroinvertebrate communities surrounding islands of the upper Mississippi River (UMR).  This is a significant shortcoming, due to the fact that additional invasive species such as the aquatic snail, Bithynia tentaculata, are currently establishing in an ecosystem already impaired by zebra mussels, Dreissena  polymorpha.  In order to address this issue, we sampled macroinvertebrate communities around a total of 16 island sites spanning Navigation Pools 7 and 8 of the UMR during the summer of 2008.  Collection sites were established based on their variability in characteristics such as island age, channel position, proximity to tributary inlets, substrate profiles, water flow, and macrophyte density.  Macroinvertebrates were exhaustively sampled on a biweekly basis at 4 points around each of the 16 island sites.  Organisms were identified and enumerated upon return to the laboratory.  Assessments of pooled data revealed important differences in the taxonomic richness of organisms across sites.  In addition, multiple-linear regression demonstrated negative correlations between taxonomic richness and the densities of both B. tentaculata and D. polymorpha.  The consequences of these relationships and the general variability of macroinvertebrate taxa in the UMR will be presented.