Feeding competition between the native oyster Crassostrea virginica and the invasive mussel Mytella charruana

The sub-tropical mussel Mytella charruana has been reported as invasive along the southeast coast of the USA since 1986. This mussel has been found to negatively impact the keystone species in its invaded range, the eastern oyster Crassostrea virginica. To date, however, no mechanism for this negative impact has been determined. To elucidate the role of the invasive mussel on economically important oyster reefs, we compared the feeding of both species in a lagoon along the east coast of Florida (USA). Three different methodologies were used: (1) in situ filter-feeding experiments using the biodeposition method to estimate feeding behavior; (2) laboratory assays to estimate the depletion of bacterial particles using a flow cytometer; and (3) stable isotope analysis in conjunction with ellipse-based metrics to investigate the niche size and overlap of these 2 species. The in situ filter-feeding experiments revealed that, compared to C. virginica, M. charruana had significantly higher clearance, filtration, rejection, organic ingestion, and absorption rates, as well as higher rejection percentage and absorption efficiency, but rejected the same amount of inorganic particles. Flow cytometry data suggested that bacteria were a food source for both bivalve species. Stable isotope values confirmed that M. charruana and C. virginica filled similar functional niches in this ecosystem. These results suggest that M. charruana can out-compete native oysters; the findings also demonstrate that an invasion of M. charruana might significantly alter plankton abundance, potentially limiting food sources available to other less efficient native filter-feeders such as clams.