Selective feeding on bivalves by<i>Polinices alderi</i>(Forbes) (Gastropoda)

Abstract

Abstract Laboratory experiments indicate that Polinices alderi (Forbes) feeds selectively when offered different species of bivalves. Shell thickness appears to be an important factor and the species with the thinnest shell, Mya arenaria L., is strongly preferred. The snails also showed size selectivity when offered different size classes of either Spisula sub-truncata (da Costa) or Spisula elliptica (Brown). The larger size classes were not preferred, although they could be handled by the predator. It is suggested that the size and shape of the bivalve, which affects ease of handling by the predator, rather than shell thickness is responsible for this result. The shell thickness of different species greatly affected the time required to drill and consume prey items of the same size. Nevertheless over a period of 14 days the snails spent a similar proportion of their time drilling irrespective of prey species. The number of bivalves which were consumed therefore depended on the shell thickness.