Influence of shelter availability on interactions between Caribbean spiny lobsters and moray eels: implications for artificial lobster enhancement

The Caribbean spiny lobster Panulirus argus is a valuable fishing resource, but local populations may be limited by availability of crevice shelter on juvenile (seagrass) habitats. This has prompted research into the potential density enhancement of juvenile lobsters with 'casitas', large (1.1 m 2 surface area) but low-lying (3.8 cm entrance height) artificial shelters that exclude large predators. Moray eels (Muraenidae), however, fit into casitas and could therefore pose a threat to lobster enhancement. In a shelter-poor reef lagoon, we examined potential interactions between juvenile lobsters and the locally dominant morays Gymnothorax vicinus and G. moringa in the absence (four 1 ha control sites) and presence of casitas (five 1 ha 'casita sites', each with 10 casitas), before (6 surveys) and after (22 surveys) deployment. Morays and lobsters did not interact as predator-prey, as morays neither consumed nor intimidated co-occurring lobsters. Rather, the 2 taxa appeared to compete for limited shelter on the reef lagoon, as suggested by a significant increase in density and mean size of both taxa on casita sites after deployment. Casitas significantly increased cohabitation of morays and lobsters, yet they tended to co-occur less often than expected by chance, but this result likely reflects behavioral differences between the highly gregarious, more numerous lobsters and the typically solitary, cannibalistic morays. Our study exemplifies the influence of habitat complexity on the nature of interspecific interactions and shows that G. vicinus and G. moringa would not pose a threat to lobster enhancement with casitas.