Fertilization in Broadcast-Spawning Corals of the Flower Garden Banks National Marine Sanctuary

Broadcast spawning is considered to be the dominant reproductive strategy for reef corals, but little is known about two critical postspawning processes, fertilization and early larval development. Instead, most efforts have focused on dispersal and recruitment. Since 1993, we have examined coral fertilization and development at the Flower Garden Banks, which contain two isolated reefs with predictable and dramatic annual mass spawning events in the northwestern Gulf of Mexico. Observations of in vitro fertilization indicate that the hermaphroditic scleractinian species Colpophyllia natans, Diploria strigosa, Monfastraea faveolata, and M. franksi all have high fertilization potentials when outcrossing. However, although D. strigosa can self-fertilize readily, self-fertilization levels within C. natans and the Montastraea species are low. In addition, interspecific crossing attempts among the hermaphroditic species of Montastraea (M. franksi, M. faveolata, and M. annularis) yielded low levels of fertilization. The differences observed in the timing of spawning and the low hybridization success between the Montastraea siblings lend additional support to their recent reclassification as separate species. Spawned egg samples collected immediately upon release from female colonies of the gonochoric species M. cavernosa and Stephanocoenia intersepta produced an unexpected observation—very high levels of fertilization. This suggests internal fertilization prior to egg release, a process that has not heretofore been observed in a broadcast-spawning scleractinian