Food regime modulates physiological processes underlying size differentiation in juvenile intertidal mussels Mytilus galloprovincialis
Feeding and growth experiments were conducted to test the hypothesis that physiological attributes responsible for size differentiation among bivalves likely vary with environmental conditions. Juvenile mussels (Mytilus galloprovincialis) were collected from an intertidal population in Biscay, Spain (43°24′42,462″N02°56′43,659″W), in January 2007 and 2009. These mussels were maintained in the laboratory under either restrictive or optimal feeding conditions until fast- and slow-growing individuals on each maintenance regime could be identified. After fast- and slow-growing individuals were identified, the components of energy balance responsible for such growth rate differences were measured. The analysis of physiological traits indicates that under optimal food supply conditions, the capacity to ingest and absorb food and associated costs of growth are the main factors underlying growth rate differences. The set of physiological differences changed when size differentiation took place under restrictive food conditions. Higher rates of absorption coupled with reduced rates of metabolism accounted for faster growth in this case, especially under low food rations.