GROWTH UNCOUPLING AND THE RELATIONSHIP BETWEEN SHELL GROWTH AND METABOLISM IN THE SOFT SHELL CLAM MYA ARENARIA

The goal of this study was to investigate whether shell growth reflect s metabolic rate rather than overall or somatic tissue production in t he soft shell clam Mya arenaria. This was accomplished by conducting l aboratory experiments exposing clams to different levels of food, imme rsion period and temperature in order to uncouple shell and soft tissu e growth, and then determining if shell growth and oxygen consumption remained positively correlated. Soft shell clams were raised in a simu lated intertidal system for 2 to 3 wk to acclimate them to experimenta l conditions. After acclimation, oxygen consumption, a measure of meta bolic activity, ingestion rate, a measure of energy intake, shell grow th and soft tissue growth were estimated for all individuals. Tissue a nd shell growth were successfully uncoupled in all experiments. In the 2 experiments where significant changes in shell growth, soft tissue growth and oxygen consumption occurred, shell growth was positively co rrelated to oxygen consumption. Soft tissue growth was either uncorrel ated or negatively correlated to oxygen consumption and shell growth. Shell transparency in thin sections increased with metabolic rate, whi le shell growth line clarity decreased in those treatments most stress ful to the clams (i.e. low food level and high temperature). Our resul ts are consistent with the hypothesis that shell growth is coupled to metabolic activity and is not a measure of somatic tissue production. We suggest that information on physiological rate processes is recorde d in the shell of bivalves, and that growth Line patterns may be used to reconstruct metabolic rates from field collected individuals.