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

Leptasterias hexactis, a sea star common in rocky intertidal areas of Puget Sound, Washington, often has damaged or missing arms. We measured the freq uency of arm damage in 5 populations and examined the causes and costs of t he 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 p arts of arms were missing, may result from physical disturbance (e.g., crus hing). Most arm damage, however, appears to result from predation by the cr ab Cancer oregonensis. The ability to lose, or autotomize, arms has adaptiv e significance if it saves a sea star from death. However, it also carries costs. The greatest cost was a decrease in reproduction. Leptasterias hexac tis 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%.