Factors affecting diet selection in the shore crab, Carcinus maenus (L.)

Abstract. Model prey were used to examine the olfactory and tactile basis of prey selection when crabs feed on resistant items such as bivalves. Shape was an important determinant of handling time which increased with height and hence cross-sectional area of the model. The additional stimulus of odour prolonged persistence time with inedible models and crabs preferred those incorporating the highest concentration of mussel, Mytilus edulis, filtrate. When presented with a sequence of edible models, crabs improved their handling skills during a foraging bout. When models were presented alternately with real mussels, however, the handling skills associated with the mussels were learned more slowly, particularly if a model was encountered first in a sequence. Crabs never rejected edible models that were encountered individually in a sequence, but frequently did so when they were encountered simultaneously in groups. During simultaneous encounters, handling time was shorter than for individual encounters. It appears that chemical cues are important attractants, and may be correlated with the probable yield and vulnerability of the prey. However, whereas olfaction is particularly important early in the attack, shape, which is the main determinant of handling time, becomes important later. Olfactory cues remain potent reinforcers throughout an attack.