Predation on Hard Clam (Mercenaria mercenaria) Populations

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Abstract
Predation on hard clams (Mercenaria mercenaria) was examined in laboratory experiments and in wild populations. Increases in clam density following predator reduction was also examined. The principal predators of hard clams are gastropods and crabs, which take mostly small clams. In the laboratory, crabs consume clams rapidly. Wild populations of clams are most abundant in areas where either predators are scarce or stones provide cover from them. Variations in recruitment and predation on clams smaller than about 15 to 20 mm determine the strength of year classes. As clams grow, they become less vulnerable to a succession of predators, first outgrowing mud crabs at a length of about 7 mm, rock crabs at about 15 mm, oyster drills at about 20 mm, and moon snails at about 50 mm. Clam densities were seven and eight times as great in sections of shellfish beds where predators were reduced by pesticide applications compared with untreated sections of the same beds.