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

Five sympatric species of intertidal decapod crustaceans were studied in the field and laboratory with regard to the mechanisms used for predator defense. The species are sympatric and represent a gradient from high intertidal (Cyclograpsus lavauxi) to subtidal (Notomithrax ursus) with Petrolisthes elongatus, Heterozius rotundifrons, and Halicarcinus innominatus intermediate in tidal distribution. We tested the hypothesis that the diversity of defensive features would increase along a tidal gradient from high to low tide. All species were scored in the field for degree of background matching in color and tendency to autotomize appendages, In the laboratory individuals were scored with regard to delay to first movement following disturbance, maximum speed of movement, maximum extent of cheliped extension, and responses to conspecific alarm odors. Maximum sizes for individuals of the different species were obtained from the published literature. The five species varied significantly in the scores recorded for all of the different defensive features. Halicarcinus innominatus matched its background significantly better, Petrolisthes elongatus autotomized the most readily, Heterozius rotundifrons 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 different features revealed that the magnitude of the overall diversity of defensive features (1) did not vary along the tidal gradient and (2) showed surprisingly little variation among the different species.