The habitat-survival function for Caribbean spiny lobster: an inverted size effect and non-linearity in mixed algal and seagrass habitats

Abstract

The habitat-survival function (HSF) defines changes in survival relative to habitat structure; forms include linear, hyperbolic and sigmoid (threshold) curves, whose consequences on predator–prey dynamics are illustrated by their first derivatives. Survival of two juvenile size classes of Caribbean spiny lobster was evaluated as a function of plant biomass in tethering experiments in mixed algal and seagrass patches adjacent to Bahía de la Ascensión, Mexico, which serves as nursery habitat. The HSF was hyperbolic for algal biomass; even modest increases of algal biomass significantly enhanced lobster survival. The rate of change in survival as a function of algal biomass (i.e. an approximation of the first derivative) was greatest at low-to-moderate levels of habitat structure. Hence, survival in these microhabitats is either low or rapidly changing with alterations in habitat structure, and they should be avoided by juveniles. Seagrass biomass did not significantly influence survival, although its levels were relatively low. Smaller juveniles had significantly higher survival rates than larger juveniles, probably because of the limited availability of appropriately scaled refugia for larger juveniles; large juveniles may display an ontogenetic shift from these habitats to coral reefs because of elevated predation risk as they grow.