Predation on hard clam (Mercenaria mercenaria) populations

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 predation on clams smaller than about 15 to 20 mm determine the strength of years classes. As clams grow, they become less vulnerable to a succession of predators, first outgrowing mud crabs at a length if about 7 mm, rock crabs at about 15mm, oyster drills at about 20mm, and moon snails at about 50mm. Clam densities were seven and eight times as great in sections of shellfish beds where predators were reduced by precide applications compared with untreated sections of same beds.