CRITERIA FOR PREY SIZE-SELECTION IN MOLLUSCIVOROUS CRABS WITH CONTRASTING CLAW MORPHOLOGIES

This paper briefly reviews our current understanding of prey size-sele ction in several families of tropical and temperate water molluscivoro us crabs. Differences in the morphological and mechanical features of crab claws reflect their function and account for many of the observed differences in prey handling techniques and foraging behaviour. Claws , however, have functions other than feeding and these can confound si mple correlations between form, strength and feeding habits. Species f eeding predominantly on rapidly moving prey typically have fast, weake r acting claws whereas those specialising on heavily-armoured mollusca n prey have claws that are slower but more powerful. Complex shell ope ning behaviour or specialised claw morphology can sometimes compensate for limited crushing power. Claw characteristics and foraging behavio ur also vary geographically; thus, compared with their temperate water counterparts, tropical crabs generally are considered to be more spec ialised for attacking hard-shelled molluscan prey, possibly as a resul t of prolonged and intense coevolution between these predators and the ir prey. Most crabs forage selectively on small-sized molluscan prey w ell below the critical size that can be opened. The reasons for such s ize-selection are not entirely clear but energy maximisation, rime min imisation, or the risk of claw damage associated with attacks on large r more resistant prey have been suggested as causal factors. The struc tural and ecological features evolved by molluscan prey that effective ly reduce the risk of predation and thus facilitate the continued coex istence of predator and prey are also briefly considered.