My students and I combine manipulative field experiments with modern laboratory techniques to address questions related to the ecology of sessile marine invertebrates. Combining a field-based approach with laboratory methods allows us to address problems at multiple scales of organization ranging from physiological to population level processes.

More specifically, research in my lab is directed into three major areas currently:

1. the role of environmental stresses, especially ultraviolet radiation, in the ecology of Caribbean corals.
2. the evolutionary and ecological importance of self-fertilization as a mode of enhancing fertilization success and recruitment rates in Caribbean corals.
3. studies of the benthic invertebrate fauna and recruitment processes at Gray's Reef National Marine Sanctuary (go here for abstracts of theses studies).

The first major area of emphasis stems from previous studies conducted by myself and others showing that many organisms living in clear, nutrient-poor tropical waters must somehow ameliorate the negative biological effects of ultraviolet-A (UV-A, 320-400 nm) and -B (UV-B, 280-320 nm) radiation. This appears especially true for reef-building corals because their nutritional reliance on photosynthetic products translocated from endosymbiotic algae (zooxanthellae) necessitates that they inhabit open reef environments where visible light intensity promotes net production of the coral. Obviously, occupying open reef areas also exposes symbiotic corals to UV radiation. While mobile marine organisms may circumvent damaging UV radiation by moving into deeper water or to more shaded locations, this option is not available to sessile organisms, such as corals, once they settle and become established. Sessile species must rely on cues at settlement to avoid high UV radiation environments or must depend on biochemical, physiological, and cellular mechanisms that either prevent UV radiation from penetrating tissues or remove resulting photoproducts and repair DNA damage.

I have investigated the role that UV radiation plays in the biology of both pre and post-settlement stages of corals. These studies were carried out in the Florida Keys where I have worked on an annual basis since 1990. The objective of the larval portion of this project was to determine if coral planulae can detect UV radiation and if this environmental parameter provides a partial explanation for species settlement patterns. These studies were conducted in the field using brooded planulae as a model system. The larval chambers pictured at right are divided into three regions that differ in their light transmission characteristics. Larvae can be added to these chambers and settlement patterns monitored over several days. These studies were conducted in collaboration with Pete Edmunds (California State University, Northridge) and Ruth Gates (University of Hawaii).

In addition to these studies I am documenting temporal and spatial variation in two sets of compounds thought to be important in countering UV radiation induced tissue damage and photosynthetic photoinhibition in reef-building corals: mycosporine-like amino acids and carotenoids. Tissue samples are being obtained from five species of reef-building corals (M. annularis, M. faveolata, M. franksi, A. cervicornis, and A. palmata) on a quarterly basis from Key Largo, FL and Lee Stocking Island, Bahamas in collaboration with Bill Fitt at the University of Georgia. Using established high pressure liquid chromatographic (HPLC) procedures a base-line data set is being produced for the types and concentrations of MAAs and carotenoids present within these coral species throughout the year. Companion studies have been conducted by two of my graduate students: Kenyon Mobley and Stephanie Schopmeyer. Kenyon investigated how heterotrophy, UV radiation, and visible light affect the abundance and distribution of carotenoids in symbiotic cnidarians. Stephanie, on the other hand, investigated the role of coral mucus in UV radiation protection.

The second major area of research emphasis has its origins in the extensive body of literature on all aspects of self-fertilization in plants. Studies on terrestrial plants range from ecological investigations of the importance of self-fertilization as a means of reproductive assurance for populations at low densities, to evolutionary theories explaining the stability and persistence of mixed (selfing and outcrossing) mating systems. While self-fertilization has been a major focus of plant ecological and evolutionary studies, very little is known concerning its importance or even its prevalence in marine invertebrates. In these studies I have collaborated with Dan Brazeau (State University of New York at Buffalo) to determine the amounts, causes, and consequences of self-fertilization in populations of three species of reef-building Caribbean corals, Agaricia agaricites, Porites astreoides, and Favia fragum.

We used random amplified polymorphic DNA (RAPD) markers to provide the first field evidence that brooding hermaphroditic Caribbean corals can self-fertilize at fairly high frequencies (>50% in some cases). We now plan to use these, and other, molecular markers to extend our results and assay rates of self-fertilization among planula larvae collected from colonies at sites differing in current regimes and population densities. These data along with results of more controlled crossing experiments will be used to examine the roles of colony size, colony genotype, population density, and current flow and intensity on rates of self-fertilization in these three species. Paternity analysis will be used to assess whether selfing results in reduced outcrossing siring success. Relative costs of inbreeding in two of the species, P. astreoides and F. fragum, will also be investigated through several measures of larval health (i.e., planula size, protein content, and lipid content) and estimates of settlement rates, growth rates, and larval survivorship under benign and suboptimal conditions. Finally, we will test the theoretical expectation that allocation to male and female function varies predictably with differences in self-fertilization rates.

Systematically evaluating the occurrence and significance of self-fertilization to the overall reproductive output of hermaphroditic reef-building corals will provide valuable insight into one of the mechanisms that may limit coral recruitment. Understanding the relationship between selfing, reproductive success and larval viability will also furnish information useful to conservationists and coral reef managers concerned with maintaining minimum population sizes and suitable colony densities. Furthermore, data collected in the course of this work can be readily compared to the vast literature on the dynamics of selfing and resource allocation in plant systems. This affords a robust test of the evolutionary and ecological theories concerning self-fertilization using organisms that are very different from those used to develop the theory. One of my graduate students, Sarah Tso, completed a masters thesis investigating another aspect of this research by quantifying and describing the breeding system of the gynodioecious Caribbean coral Porites astreoides.

The above descriptions represent a few specific areas related to the ecology of marine invertebrates in which I have been, and am currently, engaged. More generally, my long range goal is to maintain a research program that combines manipulative field experiments with modern laboratory techniques to rigorously test ecological hypotheses of both applied and theoretical significance.