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Abstract
The behavior of the sea star, Asterias forbesi, feeding on hard clams, Mercenaria mercenaria, was observed in large tanks with and without sand as a substrate for burial. The sea star captures clams by excavating them, apparently in a non-random fashion. This behavior is described. The seasonal feeding pattern of A. forbesi on buried clams was bimodal with peaks occurring in the spring and fall. Sea star digging effort (# pits/day/clam excavated during each monthly sample) varied with the average monthly temperature from Sept. 1977 to June, 1977. During March and April 1977, three day averages for number of sea star excavations varied with three day averages for the number of visible clam siphons. More clams were unearthed between the new moon and first quarter than between other phases of the moon.
A. forbesi attempted to open clams either solitarily or in aggregation. Both processes depended on the realtive sizes of predator and prey. Large clams (5->7 cm length) were generally attacked in aggregation while small clams (2–4.9 cm length) were handled by individuals. Aggregated attack was also more common when clams were buried. Aggregated attack may allow access to large clams and serve to spread resources through a population when food availability is low.