GROWTH, PHYSIOLOGICAL RATES AND BEHAVIOR OF MYTILUS-EDULIS EXPOSED TOTHE PREDATOR ASTERIAS-RUBENS

A laboratory study was made of the defensive behaviours and their bioe nergetic costs in the blue mussel, Mytilus edulis, exposed to water in which the starfish, Asterias rubens, had been kept. The shell length increase during a long-term growth assay was significantly lower for p redator-exposed mussels but was not accompanied by reduced weight incr ement, thus suggesting development towards a more compact and rounded morphology. A Scope for growth index confirmed an equal growth potenti al for predator-exposed and control mussels. Respiration, excretion an d activity were reduced and the O/N-ratio increased in predator-expose d water but these defensive behaviours were noted only at low food con centrations. Long-term predator exposure seemed to lower the risk of a mussel bring attacked by starfish in a choice assay. The growth exper iment suggests that predator-induced phenotypical change in morphology as an improvement of the mechanical protection against predators, may occur in M. edulis.