Clam-Digging Behavior in the Starfish

Abstract
The starfish, Pisastcr brevispinus, was observed to locate, dig, and eat bivalves in sand gravel substratum in Puget Sound. The tube feet were thrust through the substratum, moving sand and gravel toward the tips of the rays similarly to the tube foot motions in burrowing starfish such as Astropecten. P. brevispinus does not burrow, however, but digs a hole approximately the same diameter as the starfish and up to ten centimeters deep at the center. The mechanism by which the starfish locates the clam it not known, but the holes were accurately centered over the clams, not randomly dug. The entire digging process took two to three days in specimens observed in the field. MACGINITIE and MACGINITIE (1949) described California P. brevispinus as typically feeding on sand dollars. When placed on sand dollars in Puget Sound, P. brevispinus showed apparent irritation, but later in aquaria ate sand dollars although preferring clams. In the vicinity of Bremerton, P. brevispinus was not found associated with or bordering sand dollar beds.