SEASONAL-VARIATION IN PHYSIOLOGICAL ENERGETICS OF MYTILUS-EDULIS AND CERASTODERMA-EDULE OF DIFFERENT SIZE CLASSES

Seasonal variation of clearance, absorption and respiration rates of m ussels Mytilus edulis (Mollusca: Bivalvia) and cockles Cerastoderma ed ule (Mollusca: Bivalvia) of various size classes have been measured un der ambient temperature and sea-water conditions. Food availability wa s kept almost constant during the measurements. Allometric body weight coefficients were b(cl)=0.5 for clearance and about b(r)=0.7 for resp iration rate of both species. Stepwise multiple regression suggested n o relation for clearance rate of mussels with temperature and reproduc tive condition throughout the year. Respiration rates of mussels were highest during the reproductive period. Excretion rate was measured fo r mussels only and showed an allometric coefficient of b(ex)=0.7 and a n increase with temperature in spring. For cockles a significant relat ion of clearance rate, body weight and temperature was observed; at lo w temperature, clearance rates of small animals were more reduced than for larger animals. Respiration rates of cockles showed a significant relationship with temperature and reproductive condition.Physiology o f cockles proved to be more sensitive to low temperatures than mussels . Seasonal variation in physiological energetics of cockles depended o n temperature and reproductive condition, and showed maximum scope for growth in summer; scope for growth of mussels under conditions of con stant food availability varied throughout the year, independent of tem perature.