Abstract

The Florida stone crab, Menippe mercenaria, is an ecologically and economically important species in south Florida. The research described in this dissertation was designed to study those early-life-history processes that may affect recruitment into adult populations. Specifically, I examined: (1) timing of release of larvae by brooding females; (2) metamorphosis of larvae in nursery habitat; (3) inter-specific and intra-specific competition for food and shelter during the juvenile stage; and (4) growth during the first year after metamorphosis.

Results of the initial set of experiments showed that larval release patterns vary with location. Females from both the east and west coasts of the main Florida peninsula do not release larvae in phase with the tidal cycle and exhibit only a diurnal pattern of larval release. However, females collected in the Florida Keys release larvae during the diurnal phase of the diel cycle and near the time of the higher amplitude high tide. This localized adaptation and may facilitate transport of larvae away from spawning locations where water temperature may exceed the tolerance limits of the larvae.

Results of a second set of experiments showed that advanced-stage larvae maximize settlement and metamorphosis in nursery grounds by responding to both physical and chemical cues associated with these habitats. My study investigated the effect of water-soluble exudates from four substrata, as well as natural biofilms, and exudates from adult stone crabs. In addition, the influence of natural substrata was compared to that of artificial substrata. Adult exudate had no significant effect on metamorphosis, despite a wide range of tested concentrations. In contrast, there was a significant effect on mean time to metamorphosis in experimental groups exposed to multiple cues associated with the brown alga Sargassum fluitans, rubble from stone crab habitat, the eastern oyster Crassostrea virginica, and biofilms associated with the oyster. Furthermore, I provide evidence for metamorphic responses to water-soluble chemical cues, as well as biochemical and physical cues associated with different substrata. Overall results were consistent with previous work on metamorphosis of brachyuran crab larvae and indicated that both physical and chemical cues are important factors in facilitating the settlement and metamorphosis of M. mercenaria larvae in juvenile nursery habitat.

In a third group of experiments, I examined post-settlement events that may be important in regulating populations of the Florida stone crab, Menippe mercenaria. I investigated the prevalence of intra-cohort cannibalism among stone crab megalopae at different densities and in the presence of an alternate food source, as well as the social behaviors of first stage juvenile instars. Experiments also tested the competitive interactions of juvenile stone crabs with mud crabs (Panopeus herbstii) and blue crabs (Callinectes sapidus) of the same size. The first competition experiment gave each species access to a single shelter, while the second experiment had a piece of food as the limiting resource. My results indicate that stone crab megalopae are highly cannibalistic and that the rate of cannibalism is dependent on density. However, the presence of an alternate food source significantly decreases the incidence of cannibalism, regardless of density of the megalopae. Early instar juveniles also exhibit anti-social behavior, which is consistent with my cannibalism results. Furthermore, stone crab juveniles were shown to be dominant space competitors, out-competing both mud crabs and blue crabs for shelter. In addition, my experiments demonstrated that juvenile stone crabs are effective competitors for food, dominating the food source when in competition with mud crabs and maintaining equal access to the food when in competition with blue crabs.

In a final experiment, I determined juvenile growth curves for juvenile stone crabs reared in the laboratory. Results indicated that the rate of growth in carapace width fit a linear model and was similar in pattern to that reported for other brachyuran species. Additionally I found that growth to sexual maturity may require as much as two years from hatching and that recruitment to the fishery may not occur until the crab reach an age of nearly four years. (Abstract shortened by UMI.)