Size Selection of Mussels by the Blue Crab Callinectes sapidus: Energy Maximizer or Time Minimizer?

Abstract

Blue crabs Calllnectes sapidus Rathbun fed rapaciously on mussels Geukensia (= Modiolus) demissa (Dillwyn) in the laboratory. Very small mussels were crushed immediately, slightly larger ones more slowly across the umbonal region; all larger mussels were opened by gradually chipping the posterior edges of the shell, severing the posterior adductor and tearing the valves apart. Handling time increased with mussel volume, while profitability (yield of flesh per unit handling time) decreased monotonically as mussel size increased. C. sapidus preferred smaller to larger mussels, thereby simultaneously minimizing the time spent handling prey and maximizing the net rate of energy intake. The relative importance of 'energy maximization' and 'time minimization' could not be distinguished. C. sapidus could reduce the recognition procedure for optimal (smaller) mussels from several seconds of manipulation by the mouthparts and chelae to an instantaneous touch by a walking leg after a few minutes experience. The physico-chemlcal basis of prey evaluat~on by C. sapidus remains to be determined.