Metabolic responses to environmental salinity in the invasive clam Corbula amurensis

Invasive species can have large impacts on food webs if their metabolic demands are higher than those of extant species. The clam Corbula amurensis is believed to have caused a large shift in the pelagic food web in the northern reach of the San Francisco Estuary (USA) since its introduction in the 1980s. This shift has been attributed to the clam's high density, high suspension-feeding rates, and ability to thrive in a wide range of salinities. To understand how environmental salinity alters the potential metabolic impacts of C. amurensis on the pelagic food web, we investigated clam metabolism following acclimation to constant low, constant high, and fluctuating salinities. We measured growth rate, feeding rate, respiration rate, activity of the metabolic enzyme malate dehydrogenase (MDH), and osmoregulatory performance. Clams did not grow during a 3 mo period at either high or low salinity, although they fed more rapidly following acclimation to high salinity than low. C. amurensis had higher metabolic rates in both high and low salinity than in fluctuating salinities. Activity of MDH was positively correlated with salinity in both foot and mantle tissues. MDH activities of C. amurensis were twice those of other clam species. Osmotic pressure of C. amurensis tissues was always lower than that in the acclimation water, but clams hyporegulated to a greater extent in high-salinity conditions. Overall, our results suggest that clams experiencing higher salinities increase metabolic rates to support greater osmoregulation and compensate by increasing their filter-feeding rate.