EVIDENCE FOR HYDRODYNAMIC ORIENTATION BY SPINY LOBSTERS IN A PATCH REEF ENVIRONMENT

Western Atlantic spiny lobsters (Panulirus argus) are superb underwate r navigators. Spiny lobsters perform dramatic seasonal offshore migrat ions and have also been shown to locate and home to specific den sites within the elaborate coral reef environment in which they live. How t hese animals perform such complex orientation tasks is not known. The study reported here was designed to explore the sensory mechanisms tha t spiny lobsters use to orient in and around a familiar patch reef env ironment. Our results show that, in the absence of visual cues, lobste rs displaced a short (50 m) distance off the reef do not initially (i, e. within 20 min) travel towards their dens or return to the patch ree f where their dens are located. Instead, the headings lobsters follow are significantly correlated to the direction of local hydrodynamic cu es and, specifically, to the direction of approaching wave surge. Resu lts from ultrasonic tracking experiments over longer periods (24 h) su ggest that displaced lobsters are able to relocate the reef where they were captured, even without visual cues. These results suggest that h ydrodynamic cues may provide useful and immediate directional informat ion to lobsters within the local environment of the home reef.