A comparative study of the defense syndromes of some New Zealand marine crustacea

Five sympatric species of intertidal decapod crustaceans were studied in th e field and laboratory with regard to the mechanisms used for predator defe nse. The species are sympatric and represent a gradient from high intertida l (Cyclograpsus lavauxi) to subtidal (Notomithrax ursus) with Petrolisthes elongatus, Heterozius rotundifrons, and Halicarcinus innominatus intermedia te in tidal distribution. We tested the hypothesis that the diversity of de fensive features would increase along a tidal gradient from high to low tid e. All species were scored in the field for degree of background matching i n color and tendency to autotomize appendages. In the laboratory individual s were scored with regard to delay to first movement following disturbance, maximum speed of movement, maximum extent of cheliped extension, and respo nses to conspecific alarm odors. Maximum sizes for individuals of the diffe rent species were obtained from the published literature. The five species varied significantly in the scores recorded fur all of the different defens ive features. Halicarcinus innominatus matched its background significantly better, Petrolisthes elongatus autotomized the most readily, Heterozius ro tundifrons showed the longest periods of immobility following disturbance, Cyclograpsus lavauxi could move the fastest, and Notomithrax ursus reached the largest size. However, all species utilized multiple mechanisms related to predator avoidance. Summation of the rank scores for the seven differen t features revealed that the magnitude of the overall diversity of defensiv e features (1) did not vary along the tidal gradient and (2) showed surpris ingly little variation among the different species.