Influence of conspecifics on the ontogenetic habitat shift of juvenile Caribbean spiny lobsters

Abstract

Werner and Gilliam’s (1984) model predicts that size-specific rates of growth and mortality determine the size at transition for animals with an ontogenetic habitat shift (OHS). Although animals are unlikely to calculate mortality rate, they often respond to changes in predation risk. For many social species, an individual’s risk of predation is reduced by conspecific aggregation. We hypothesize that individuals in groups respond to this reduction of predation risk and should shift habitats at a smaller size than solitary individuals. We tested this hypothesis by altering food availability, predation risk and conspecific presence for newly settled spiny lobsters in mesocosms. Juvenile Caribbean spiny lobsters, Panulirus argus, undergo an ontogenetic habitat shift from algal dwelling to crevice sheltering concomitant with aggregation in crevices. We found that juveniles raised with low food availability and low predation risk underwent transition at a smaller size. We also found that juveniles raised with conspecifics underwent transition at a smaller size than did solitary lobsters under the same conditions. Our results suggest that the ontogenetic habitat shift of algal-phase lobsters is accelerated when food is scarce, predation risk is low, and conspecifics are present. In the absence of conspecifics, algal lobsters wait until they are larger to change from algal dwelling to crevice sheltering. This result suggests that ontogenetic habitat shifts for gregarious animals are influenced by the proximity of conspecifics.