DEN SHARING BY JUVENILE CARIBBEAN SPINY LOBSTERS (PANULIRUS-ARGUS) INNURSERY HABITAT - COOPERATION OR COINCIDENCE

Spiny lobsters (Palinuridae) commonly share crevice shelters with cons pecifics, a behaviour usually hypothesized to benefit mutually coopera tive defenders through reduced predation risk. The group-defence hypot hesis predicts a suite of distinct corollary life history traits and e cological correlates including more frequent co-denning than solitary denning, especially where predators or den competitors are numerous an d when the lobsters are small, moulting or otherwise vulnerable. Two a lternative co-denning hypotheses, the dilution effect (a type of selfi sh herding) and the guide effect (attraction to a denned conspecific), have different and distinctive sets of predictions. To test among the se hypotheses, the den-sharing patterns of newly emerged postalgal juv eniles of Panulirus argus and associated ecological conditions in the Florida Bay (USA) nursery habitat were examined. Only half of the juve niles shared dens, and rarely was den sharing in an area greater than that expected by chance. Den-sharing frequency was most highly correla ted with conspecific density and scarcity of local dens. The lack of c orrelation between den sharing and lobster size, moult condition, shel ter type and predator density failed to support either the group-defen ce or the dilution-effect hypothesis. Instead, the data better support the guide-effect hypothesis.