Abundance of an invasive bivalve, Corbicula fluminea, is negatively related to growth of freshwater mussels in the wild

Causes of worldwide freshwater mussel declines are poorly understood, and the potential role of the invasive Asian Clam, Corbicula fluminea, has received little attention. We measured survival and growth of captively-reared juveniles of four native mussel species during 84-day in situ exposures at 17 sites in the Rockcastle River system, Kentucky, U.S.A., where mussel declines are attributed to coal mining. We measured water temperature, a comprehensive array of water chemistry variables, and Corbicula abundance at each site during mussel exposures. Mussel survival was high (mean = 85.4%), did not differ among species, and was not related to any measured factor. In contrast, growth varied among sites by an order of magnitude, but growth responses were nearly identical for all four species. We found little evidence of water pollution from coal mining or other sources, and pollution did not explain variation in mussel growth. Growth was best explained by a model including only temperature (positive effect) and Corbicula abundance (negative effect) without interaction. Our model predicts 46% lower mass gain over 84 days for every 10-fold increase in Corbicula abundance regardless of temperature, but growth may be reduced to unsustainably low levels in cooler streams. Previous ideas about water pollution as a cause of low growth and mussel declines were not supported by our data. Instead, the predicted strong effects of Corbicula, combined with similar responses of four mussel species, suggest that Corbicula may be an important, but overlooked, factor in widespread mussel declines.