Virginia Institute of Marine Science
A principal mechanism underlying a production hypothesis that artifical reefs increase environmental carrying capacity and eventually the biomass of reef-associated organisms is that these structures reduce predation on reef residents. We tested this predation mechanism with a series of field experiments at two sites (inner-bay sand-seagrass flat, and outer-bay seagrass bed adjacent to coral reefs) in Bahia de la Ascension, Mexico. We examined survival of two size-classes of juvenile Caribbean spiny lobster Panulirus argus tethered in seagrass beds with and without access to artificial lobster shelters, and at different distances from the shelters. The artificial shelters were concrete structures (casitas) that simulate lobster dens. Large juvenile lobsters (56-65 mm CL) attained a relative size refuge when tethered 60 m away from casitas compared with smaller (46-55 mm CL) lobsters. Conversely, the small lobsters survived better beneath casitas than did large lobsters. Small juveniles also survived better at casitas or 30 m away from casitas than at 15 m or 70 m away. Observations indicated that the daytime predator guild, composed primarily of snappers (family Lutjanidae), seldom foraged more than 60 m from casitas and were typically within 15 m of casitas. There was also a significant positive correlation between predation-induced lobster mortality and numbers of snapper associated with casitas at the inner-bay site. Thus, tethering lobsters 70 m away from casitas appeared adequate to examine survival of lobsters in an environment uninfluenced by daytime predators aggregating to casitas. These results indicate that (1) the relative importance of a lobster-size refuge from predators varies according to shelter availability, and (2) that there is a nonlinear relationship between predation risk and distance from an artifical shelter. Our results demonstrate that casitas increase survival of small juvenile lobsters but reduce survival of larger juveniles. Small casitas scaled according to body size may enhance survival of large juvenile lobsters in nursery habitats where large conspecifics are removed from large casitas.
Eggleston, David B.; Lipcius, Rom; and Miller, DL, "Artificial Shelters And Survival Of Juvenile Caribbean Spiny Lobster Panulirus-Argus - Spatial, Habitat, And Lobster Size Effects" (1992). VIMS Articles. 603.