Effects of Suspended Sediment on Growth, Respiration, and Excretion of the Soft-Shell Clam (Mya arenaria)

Abstract

In long-term exposures for 35 d, soft-shell clams (Mya arenaria) were maintained in a flow-through suspension of intertidal sediment (100–200 mg∙L−1) and in a control treatment of ambient sand-filtered seawater, each with microalgae as a food source. Weekly measurements demonstrated a significant decrease in oxygen consumption and increase in ammonia excretion through time in the turbidity treatment compared with controls. Atomic O:N ratios fell to 14 for exposed clams and remained at 27 for controls, suggesting that exposed clams were utilizing body reserves to meet nutritional needs. Dry tissue weight showed no difference between initial and final values in the presence of suspended sediments, but control animals grew by 43%. In short-term exposures to 0–2000 mg suspended sediments∙L−1, oxygen consumption declined sharply with sediment concentration, suggesting that inhibition of respiration occurred at low values of turbidity. In further short-term observations, the threshold for the production of pseudofeces was 100–119 mg∙L−1. These results suggest that Mya arenaria copes with increased turbidity by reducing its ventilation rate, a response which provides tolerance to intermittent turbidity, but causes starvation during long-term exposure.