Trophic niche space of a native mussel and Corbicula fluminea in a coastal plain stream

Filter-feeding mussels link the water column and benthic zones in aquatic systems, and historically comprised the majority of benthic biomass in many North American streams.  The invasive bivalve, Corbicula fluminea, has the potential to profoundly alter organic matter dynamics, yet little is known about differences in their feeding ecology relative to native unionid mussels.  In this study, we compared the stable isotopic signatures of C. fluminea and a native freshwater mussel, Elliptio crassidens.  We used a multi-response permutation procedure (MRPP) as an omnibus test of equality between species’ stable isotopic signatures.  Whenever the MRPP test indicated a difference in trophic use, Van Valen’s test was used to determine if the distribution of isotopic signatures expanded or contracted (i.e., dispersion changed), and descriptive statistics were used to determine if the distribution of signatures shifted (i.e., central tendency changed).  We hypothesized that C. fluminea, given their invasive properties, would assimilate a larger range of materials.  Our results indicated these two species did have differences in assimilation of the food resources.  The invasive species, C. fluminea, occupied a larger trophic niche space and assimilated a higher diversity of organic particulates as indicated by the large range of isotopic signatures than did E. crassidens.