A comparison of the strengths of gastropod shells with forces generated by potential crab predators

Carcinus manenas, Liocarcinus puberandCancer pagursare thought to be three likely crab predators of the gastropodCalliostoma Zizyphinum.In order to compare the strenghts of predators and their prey, the whole shell and aperture lip strengh of white and pinkCalliostomamorphotypes and the maximum forces exerted by the chelipeds of three crab species were measured. Although white shells were thicker than pink shells,Calliostomacolour morphotyes did not differ significantly in either the force required to break the shell lip or the whole shell. BothLiocarcinus puberandCarcinus maenashave dimorphic chelipeds and their “crusher” chelipeds deliver almost double the forces generated by the‘cutter’chelipeds. In constrast,Cancer pagurushas monomorphic chelipeds both delivering similar forces. When compared withCalliostomashell strenght, the forces generated by the‘crusher’chelipeds of mostL. pubertested were, in general, sufficient to break the shell lip ofCalliostomashells, whereas forces generated by the‘cutter’chelipeds of only the larger individuals were sufficient to break the shell lip. InC. manenas, forces generated by both the‘cutter’and‘crusher’chelipeds often exceeded the minimum recorded force required to break the shell lip and the‘crusher’cheliped reached the minimum force required to break wholeCalliostomashells. Both chelipeds of allC. pagurustested generated forces in excess of the minimum required to break the shell lip, and the proportion of individuals capable of generating the minimum force required to break the whole shell increased with the size of the size of the crab.Carcinus maenasandCancer paguruswere capable of breaking both the shell lips and the whole shells of a wider range of shell sizes thanL. puber.