Reproduction and phylogeography of two scleractinian corals in the Western Atlantic

Reproductive processes have biogeographic and evolutionary implications. Such processes can vary geographically, thereby affecting local and regional population demography. Planulation by the coral Favia fragum at its distributional extreme, Bermuda, was examined for effects of geographic location on reproductive timing. Lunar synchronization of planulation in Bermuda was similar to that found in Puerto Rico, suggesting no effect of geographic location on lunar periodicity. Fecundity of F. fragum in Bermuda and Puerto Rico was also similar; however, reproduction was limited to summer months in Bermuda, suggesting that annual fecundity may be reduced at high latitude locations. Diel patterns of planulation and latent effects associated with release time, such as competency, settlement, growth, and mortality were also analyzed. Peak planulation occurred shortly before dawn, and planulae released at that time compared to those released close to sunset had higher competency rates, higher settlement rates, lower mortality, and higher initial growth rates. The benefits of pre-dawn release likely result from immediate exposure to light as a settlement cue and as a source of symbiont-derived photosynthetic products. Additionally, population structure of two coral species across the Caribbean and Bermuda was examined using multilocus sequence data and skeletal morphology. The brooding coral, F. fragum, which has a larval life stage shorter than 48 hours, showed high genetic structure and limited gene flow among locations. Furthermore, a single unique sequence type was found for all individuals from Bermuda, which also varied morphologically from all other locations. These results indicate that populations of F. fragum rely on local recruitment and that isolated populations such as those in Bermuda are "closed". Conversely, the broadcasting coral, Montastraea cavernosa, which has a larval life of several days to weeks, had high degrees of genetic connectivity within and among locations. The presence of private haplotypes and significant F ST comparisons, however, suggest that although gene flow among locations is high, populations are also partially maintained through self-seeding. Variations in skeletal anatomy found among certain locations are likely due to depth-related phenotypic plasticity. Information on connectivity among reefs indicates resilience to disturbance events and will assist in conservation efforts of theses threatened ecosystems.