Causes and consequences of arm damage in the sea star Leptasterias hexactis

Abstract

Leptasterias hexactis, a sea star common in rocky intertidal areas of Puget Sound, Washington, often has damaged or missing arms. We measured the frequency of arm damage in 5 populations and examined the causes and costs of the damage. Between 30 and 46% of L. hexactis found at the study sites were missing arms or parts of arms. Some of the damage, particularly when only parts of arms were missing, may result from physical disturbance (e.g., crushing). Most arm damage, however, appears to result from predation by the crab Cancer oregonensis. The ability to lose, or autotomize, arms has adaptive significance if it saves a sea star from death. However, it also carries costs. The greatest cost was a decrease in reproduction. Leptasterias hexactis missing arms showed a 44-69% drop in egg production 7 months after arm loss. The effect was still evident during the next reproductive season (19 months after arm loss). We estimate that natural levels of arm damage could decrease the reproductive output of a population of L. hexactis by 7-10%.