Survival of juvenile Caribbean spiny lobster: effects of shelter size, geographic location and conspecific abundance

The Caribbean spiny lobster Panulirus argus seeks structured shelter throughout its benthic phase, often forming aggregations within shelters. Casitas - concrete, low-relief, artificial shelters - are effective in aggregating lobsters, and are used to harvest spiny lobster in the Caribbean. However, casitas may also enhance populations of P. argus, by providing shelter from predation. In this study we examined the effects of various shelter features upon the survival of juvenile P. argus. Juvenile lobsters were tethered at several artificial shelter treatments in Florida Bay, Florida, USA, to test the efficacy of casitas as refuge from predation. Survival of juveniles was analyzed with respect to 4 shelter types (2 casita sizes, a simulated natural shelter and a no-shelter control) within 2 locations in Florida Bay. In general, casita availability significantly increased survival. The geographic location of artificial shelter placement also significantly affected survival; the degree of survival enhancement was apparently linked to the availability of natural shelter. Furthermore, there was a quantitative relationship between lobster survival and lobster abundance within shelters, which was tempered by local predation pressure. Survival of tethered individuals was highest when the number of conspecifics was high and predator abundance was low. While larger shelters allowed for larger lobster aggregations and usually contained more lobsters, lobsters tethered to large shelters that contained relatively few conspecifics sustained higher mortality, probably due to their increased vulnerability to larger casita-associated predators. Thus, the survival of juvenile P. argus is controlled not only by physical features of the shelter, but also by the relative abundance of conspecifics and predators in shelter-providing habitats