Interdependence of connectivity, genetic diversity and the effective population size of Montastraea faveolata across the Florida Keys National Marine Sanctuary: A microsatellite analysis

Coral reef species have the potential to disperse their larvae over large distances. Recently, though, the distance that reef-building species actually disperse has come into question. Several authors have noted that while corals have the potential for high dispersal, they rarely realize their capability and that many reefs may be more dependent on local production and recruitment of larvae. In Chapter 1, I tested the possibility that small-scale population structure exists within reefs. The Florida Keys National Marine Sanctuary (FKNMS), an area that can presumably draw larvae from multiple regions within the Caribbean, served as a model to understand gene flow and genetic diversity using a coral species with pelagic larvae. Gene flow and connectivity were assessed among populations of Montatraea faveolata on a relatively small scale in the context of geographic distance between populations, environmental conditions (deep and shallow environments) and local ocean circulation patterns using 6 microsatellite loci. Population subdivision was detected for M. faveolata on a relatively fine scale, though distance between populations, differences in current patterns, and differences in depth failed to explain the observed population structure.; In Chapter 2, I tested the possibility that genetic diversity and the age-structure of M. faveolata could explain some of the population sub-division that was estimated in Chapter One. Age was estimated for each colony of M. faveolata and was placed into one of four 40-year generation bins. Genetic diversity was estimated as the number of alleles per age bin and the proportion of expected (HE), and observed (H O) heterozygotes from six microsatellite loci contained in the age bin.; Despite large fluctuations in population size in the FKNMS, no general decrease in Ne, was detected for the overall Keys population. A decrease in genetic variation was observed when individual heterozygosity was correlated by size, but was not observed for HE or Na between generations. With no change in HE or Na, a reduction in individual heterozygosity is most likely due to other factors related to selection and inbreeding depression instead of reduced genetic diversity. Self-fertilization, on the other hand, while rare, may increase due to loss of inter-colony competition. This was supported by the high and positive FIS values in the lower Keys.; The intention of Chapter 3 was to gain insight on genetic decline by modeling the effective population size (Ne) for coral populations in the Caribbean Region. The model isolated three factors: fecundity as inferred by size structure, partial mortality and its effect on generation time, and survivorship. Based on the model, coral populations that had large mean colony size and high size/partial mortality covariance had lower overall Ne values. The model illustrated that coral populations vary in their Ne but not drastically. While some authors advocate assuming most populations are close to N/2, for corals at least, this does not seem to be accurate. In fact, despite severe environmental degradation and almost universal population decline the ratio Ne:N is greater than N/2 for most populations modeled here.