Abstract

The subtidal predators Leptasterias polaris and Asterias vulgaris strongly overlap in their size, distribution and use of prey resources. We evaluate the factors determining their use of prey (feeding rate and prey selection) by comparing prey use in the laboratory and in the field. Both seastars have the same preferred prey, the mussel Mytilus edulis, select medium-sized mussels (1.5-3.0 cm), and show similar responses to increasing mussel density (functional response). Differences between the two seastars in their feeding abilities appear to affect both their size selection of mussels and use of alternative prey when mussels become rare or absent. A. vulgaris selects larger mussels than L. polaris when mussel abundance is low, and this may optimize its energetic intake. L. polaris is be better able to prey on the crevice-dwelling clam Hiatella arctica and A. vulgaris on the ophiuroid Ophiopholis aculeata. These differences in prey selection may reduce potential competitive interactions between the two seastars, as they cause prey partitioning when the preferred prey is rare or absent. The greater feeding rate of A. vulgaris on larger mussels likely provides it with a competitive advantage when the abundance of preferred prey is limited. (C) 2001 Elsevier Science B.V. All rights reserved.