Behavioural responses of predatory crabs and sea stars to varying density of juvenile sea scallops

The effect of density of juvenile sea scallops (Placopecten magellanicus; 0 -45 scallops m(-2)) on behavioural responses of predatory crabs (Cancer irr oratus) and sea stars (Asterias vulgaris and A. forbesi) was examined in an experiment using tethered scallops in Lunenburg Bay, Nova Scotia, Canada. Within experimental plots (4 m(2)), mortality of tethered scallops, density of shell remains of unattached scallops, and density of predators were mon itored to determine the functional and aggregative responses of crabs and s ea stars. The cause of mortality (crab or sea star predation) could be iden tified from the scallop shell remains. Predation rate on scallops increased significantly with scallop density, but predator density did not. Thus, pr edators displayed a functional response, and not an aggregative response. P roportional mortality of scallops indicated that crab predation tended to b e positively density-dependent, whereas sea star predation was density-inde pendent. The results of this study are relevant to bottom culture operation s and indicate that crabs would have a greater impact than sea stars on see ded populations of scallops. (C) 1998 Elsevier Science B.V. All rights rese rved.