Predation on Littorina Irrorata (Mollusca:Gastropoda) by Callinectes Sapidus (Crustacea: Portunidae)

Callinectes sapidus swim to the surface in the intertidal zone during high tide, and remove Littorina irrorata adhering to plant stems near to and above the water line. Snails are carried to the bottom, cracked open, and eaten. Laboratory observations indicate specialized roles for each of the morphologically different chelipeds during shell opening. Concentration of predation on snails of a particular relative size is suggested by analysis of opercula in cardiac stomachs, and may be partly related to maximizing the amount of food obtained per unit time. The movement of L. irrorata up plant stems on an advancing tide probably serves as a defense against predation by C. sapidus, Melongena corona, and possibly other predators.