High incidence of limb autotomy in a crab population from a coastal lagoon in the province of Buenos Aires, Argentina

Abstract

A total of 2243 individuals of the shore crab Cyrtograpsus angulatus were obtained from Mar Chiquita lagoon, in the province of Buenos Aires, Argentina, from August 1986 to May 1987. Adult crabs were found at low tide on stones or on the beach, whereas juveniles were found beneath stones. Each crab was measured, sexed, and examined for the incidence of autotomized and regenerated limbs. Crabs exhibited a high, although size dependent, incidence of autotomy that was higher in female than in male adult crabs; the lowest values were found in juveniles. Crabs lost from one to seven limbs; both sexes showed a higher number of multiple, and a reduced number of single, autotomies than expected. The highest incidence occurred in the longest and most exposed limbs: the third and fourth walking legs; the chelae showed a reduced incidence. Crabs with multiple autotomy lost adjacent rather than nonadjacent limbs. The regeneration of a lost limb did not depend on the number of autotomies in small crabs, but it did in the case of large crabs which frequently did not regenerate some of their lost limbs. The five pairs of limbs had similar, size dependent, incidence of regeneration. Adult crabs with multiple autotomies had a lower proportion of synchronous regeneration of adjacent limbs. The high incidence of autotomy in this population of C. angulatus is discussed and alternative explanations of its causes are proposed, namely, inter- and intra-specific predation and agonistic behaviour.