Behavioral responses to variable predation risk in the California spiny lobster Panulirus interruptus

Shelter dwelling and gregariousness are behavioral strategies used by benthic marine organisms to reduce the risk of predator-induced mortality. For spiny lobsters, the relative and synergistic success of shelter dwelling and aggregation in reducing mortality may vary with the perceived risk of predation as well as the availability and size distribution of conspecifics and shelters. We tested how these factors influence antipredator behavior in the California spiny lobster Panulirus interruptus in southern California kelp forests. We measured shelter and lobster characteristics, predator density, relative lobster mortality outside of shelter, and quantified lobster antipredator behaviors in (1) the La Jolla Ecological Reserve (LJER), a marine protected area with high densities of large fishes known to be lobster predators, and (2) the Point Loma kelp forest, a nearby, heavily fished area. Predator densities and the relative mortality of tethered juvenile and adult lobsters were much higher in the LJER than in Point Loma, as was mean lobster size. In response to higher predation risk, solitary lobsters in the LJER used shelters more closely scaled to their body size than lobsters in Point Loma, thereby restricting predator access to shelters. In addition, aggregations of 2 or more lobsters were more frequent than expected by chance in the LJER, but not in Point Loma. Lobsters in Point Loma commonly were found outside of shelter during the day, whereas no lobsters ever were observed outside of shelter during daylight hours in the LJER. Overall, our results indicate that California spiny lobsters modify their antipredatory behaviors with level of predation risk and that behaviors designed to minimize predator-induced mortality are similar between California spiny lobsters and other spiny lobster species.