PHYSIOLOGICAL-RESPONSES OF INFAUNAL (MYA ARENARIA) AND EPIFAUNAL (PLACOPECTEN-MAGELLANICUS) BIVALVES TO VARIATIONS IN THE CONCENTRATION ANDQUALITY OF SUSPENDED PARTICLES-II - ABSORPTION EFFICIENCY AND SCOPE FOR GROWTH

Placopecten magellanicus, an epibenthic scallop, and Mya arenaria, an infaunal clam were studied to compare their physiological responses to variations in the quantity and quality of suspended food. The two biv alve species were exposed, simultaneously, to four concentrations of s eston (1, 3, 7 and 14 mg l(-1)) at each of three levels of organic qua lity (25, 50 and 80%) for several days. Experimental diets consisted o f mixtures of microalgae and silica at concentrations typical of those observed in their natural habitats. Absorption efficiency (AE) was no t significantly different between scallops and clams. In both species, AE was independent of concentration, and increased as the organic fra ction of the seston increased. Oxygen consumption and ammonia excretio n were also similar for both scallops and clams, and there was no cons istent effect of concentration or food quality on these metabolic proc esses for either species. Scope for growth (SFG) in both species incre ased at a decreasing rate with elevated particle concentrations and or ganic content of the seston until an asymptote was reached. SFG in sca llops was equal or exceeded SFG in clams at low concentration, but the opposite was true at high concentrations. Mya arenaria appeared to be better suited than Placopecten magellanicus to cope with higher conce ntrations of seston, especially if it consisted of relatively poor qua lity particles. (C) 1998 Elsevier Science B.V.