Seasonal and spatial variation in the energetics of the invasive clam Corbula amurensis in the upper San Francisco Estuary

Predicting the impacts of invasive species on native communities requires an understanding of the energy requirements of the community members and the strength and direction of energy flows within the ecosystem. The Asian clam Corbula amurensis invaded the San Francisco Estuary (SFE) in 1986 and is implicated in the decline of native fish species, by diverting pelagic productivity to the benthos through filter feeding. We sought to characterize how energetic demands of C. amurensis respond to natural seasonal and spatial variation in salinity, and how this response may be influenced by variation in temperature and food availability. We found that metabolic rates of C. amurensis vary seasonally and spatially within the estuary, but temperature, salinity, and food availability explain little of the variability. The insensitivity of metabolism to salinity suggests a re-evaluation of the importance of this environmental factor in determining the distribution of C. amurensis in the SFE. Though C. amurensis did hyperosmoregulate under low salinity conditions, the potential costs of this activity were not associated with changes in metabolic rate or energy stores (glycogen). Current knowledge suggests that under natural food, temperature, and salinity regimes in the SFE, the distribution of adult C. amurensis is not likely a consequence of the energetic costs of salinity tolerance. However, the role that food availability plays in modulating salinity tolerance, especially at different temperatures, deserves additional attention.