Growth, physiological rates and behaviour of mytilus edulis exposed to the predatorAsterias rubens

A laboratory study was made of the defensive behaviours and their bioenergetic 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 predator‐exposed mussels but was not accompanied by reduced weight increment, thus suggesting development towards a more compact and rounded morphology. A Scope for growth index confirmed an equal growth potential for predator‐exposed and control mussels. Respiration, excretion and activity were reduced and the O/N‐ratio increased in predator‐exposed water but these defensive behaviours were noted only at low food concentrations. Long‐term predator exposure seemed to lower the risk of a mussel being attacked by starfish in a choice assay. The growth experiment suggests that predator‐induced phenotypical change in morphology as an improvement of the mechanical protection against predators, may occur in M. edulis.