| Like their Indo-Pacific counterparts, western Atlantic coral reefs exhibit predictable annual mass spawnings. In this study spawning events at the Flower Gardens (northwestern Gulf of Mexico), are described. At this site, highly synchronized multi-specific spawning episodes occur each summer, around a last quarter moon. Spawning by each of the eleven invertebrates takes place on certain evenings, during brief (30 to 120 min) windows. Although overlap in the timing of spawning occurs, its extent among closely related species is minimal, reducing the likelihood of hybridization. Among simultaneous hermaphroditic corals (Colpophyllia natans, Diploria strigosa, Montastraea annularis, M. faveolata and M. franksi), outcrossing yields higher estimates of fertilization than either selfing within, or hybridization between, species. In the gonochoric spawners, Montastraea cavernosa and Stephanocoenia intersepta, fertilization may be internal. Fertilization in spawned egg samples exceeds those characteristic of hermaphroditic corals; male colonies initiate spawning earlier than females, providing time for sperm to reach female colonies. Development of five coral species is characterized. Initially utilizing a pseudo-spiral cleavage pattern, cellular divisions beyond the 64-cell stage become asynchronous. Gastrulation begins within 12 to 15 hours after fertilization and planulae are fully differentiated within 48 hours. Recruitment of D. strigosa planulae derived from spawned gametes onto artificial substrates met with limited success, demonstrating a potential application for reef restoration efforts.; Connectivity among the Flower Gardens and coral reefs in the southwestern Gulf of Mexico and on the Yucatan's Caribbean coast was assessed by sequencing the mitochondrial control region of two fish species. Estimates of genetic divergence among populations for species with planktonic durations of 20 days (Stegastes partitus) or up to 80 days (Thalassoma bifasciatum) indicate no substructure (Fst = 0.0–0.02). AMOVA confirmed that genetic variation is distributed between sampled reefs and is not restricted to specific locations. Estimates of migration rates between sampled sites are substantial. However, migration does not represent a significant source of larval input in terms of population maintenance at the Flower Gardens. Rather, large-scale transient circulation features on the outer continental shelf provide mechanisms of localized retention at the Flower Gardens. |
