Gabriel A. Delgado

Predator-Induced Behavioral and Morphological Plasticity in the Tropical Marine Gastropod Strombus gigas

Florida queen conch stocks once supported a significant fishery, but overfishing prompted the state of Florida to institute a harvest moratorium in 1985. Despite the closure of the fishery, the queen conch population has been slow to recover. One method used in the efforts to restore the Florida conch population has been to release hatchery-reared juvenile conch into the wild; however, suboptimal predator avoidance responses and lighter shell weights relative to their wild counterparts have been implicated in the high mortality rates of released hatchery juveniles. We conducted a series of experiments in which hatchery-reared juvenile conch were exposed to a predator, the spiny lobster (Panulirus argus), to determine whether they could develop behavioral and morphological characteristics that would improve survival. Experiments were conducted in tanks with a calcareous sand substrate to simulate a natural environment. Conditioned conch were exposed to caged lobsters while conch in the control tanks were exposed to empty cages. Conditioned conch moved significantly less and buried themselves more frequently than the naive control conch. Morphometric data indicated that the conditioned conch grew at a significantly slower rate than the naive conch, but the shell weights of the two groups were not significantly different. This implies that the conditioned conch had thicker or denser shells than the control group. As a result, the conditioned conch had significantly higher survival than naive conch in a subsequent predation experiment in which a lobster was allowed to roam free in each tank for 24 hours. In the future, the conditioning protocols documented in this study will be used to increase the survival of hatchery-reared conch in the wild.

Predator-Prey Interactions Between the Corallivorous Snail Coralliophila abbreviata and the Carnivorous Deltoid Rock Snail Thais deltoidea

Coral reefs in the Florida Keys have become highly degraded in recent decades, prompting efforts to reestablish populations of vital reef-accreting corals to restore reef structure and ecological function. However, predation on these corals by the corallivorous gastropod Coralliophila abbreviata has been a substantial and chronic impediment to these restoration efforts. We conducted laboratory experiments to determine whether Thais deltoidea, a carnivorous gastropod that commonly occurs with C. abbreviata, is a predator of C. abbreviata. We demonstrated that T. deltoidea readily preys upon C. abbreviata and preferentially targets smaller individuals, a foraging behavior that may optimize the energy gained due to reduced handling and consumption times. If this trophic relationship proves ecologically relevant, understanding the predator-prey dynamics between these species could ultimately aid in the development of a comprehensive coral reef restoration strategy for Florida.

Effects of mosquito control pesticides on competent queen conch (Strombus gigas) larvae.

Pesticides are applied seasonally in the Florida Keys to control nuisance populations of mosquitoes that pose a health threat to humans. There is, however, a need to investigate the effects of these pesticides on non-target marine organisms. We tested naled and permethrin, two mosquito adulticides used in the Keys, on a critical early life-history stage of queen conch (Strombus gigas). We conducted 12-h exposure experiments on competent (i.e., capable of undergoing metamorphosis) queen conch larvae using environmentally relevant pesticide concentrations. We found that there was little to no mortality and that the pesticides did not induce or interfere with metamorphosis. However, after introduction of a natural metamorphic cue (extract of the red alga Laurencia potei), a significantly greater proportion of larvae underwent metamorphosis in the pesticide treatments than in those with the alga alone. In addition to the morphogenetic pathway that induces metamorphosis when stimulated, there thus appears to be a regulatory pathway that enhances the response to metamorphic triggers, as suggested by the increased sensitivity of the queen conch larvae to the algal cue after pesticide exposure (i.e., the pesticides stimulated the regulatory pathway). The regulatory pathway probably plays a role in the identification of high-quality habitat for metamorphosis, as the increased response to the algal cue suggests. Aerial drift and runoff can carry these pesticides into nearshore waters, where they may act as a false signal of favorable conditions and facilitate metamorphosis in suboptimal habitat, thus adversely affecting recruitment in nearshore queen conch populations.