Food quality in low-gradient streams of the southeastern coastal plain is controlled by streamflow, connectivity to the floodplain, and the position within the watershed. These important abiotic factors structure streams along with co-occurring biotic interactions. Freshwater mussels are a dominant invertebrate in these streams and have the ability to alter the availability and quality of basal food resources through their filtration and excretion activities. Corbicula fluminea, an invasive bivalve species, has become established throughout North America and has the potential to alter available food resources. This study examined the functional roles of Elliptio crassidens (native) and C. fluminea. Both species selected for organic, living materials over inorganic, non-living materials, however these species assimilated different resources into their tissues as reflected by their stable isotopic signatures. Additionally, C. fluminea released more nitrogen back into the sediments through biodeposits. This research indicates the need to understand more about invasive species functional roles.