Decision of the asteroid Leptasterias polaris to abandon its prey when confronted with its predator, the asteroid Asterias vulgaris.

We examined the decision of the asteroid Leptasterias polaris to abandon its bivalve prey Spisula polynyma when confronted with the predatory asteroid Asterias vulgaris. The frequency of abandonment decreased as the proportion of prey ingested increased from 10 to 40%, and increased with further increases in proportion of prey ingested. The escape response of L. polaris appears to be a compromise between risk of predation and benefits of feeding. This increase in the frequency of abandonment as the prey became further consumed beyond 30-40% likely represented decreasing benefits in the face of continued risk of predation. We propose that the initial decrease in fleeing as the proportion of prey eaten increased from 10 to 40% was because of a decreasing costs in subduing the prey, as there was a coincident decrease in the proportion of prey which were still capable of holding their valves closed.