Every summer around the August full moon, a remarkable and little understood phenomenon takes place on the coral reefs. All at one time, a number of species of branching and stony corals spawn, filling the waters with tiny round eggs and a cloud of sperm. Although generally asexual in their reproduction, meaning that during the year they simply divide into exact genetic replicas, the corals have apparently set aside this one night of the year for sexual reproduction.
The fact that corals even had such a night life wasn't discovered until the 1980s in Australia. It was first documented in North America in 1990 at the Flower Gardens National Marine Sanctuary in the Gulf of Mexico. Since then, the spectacle has been observed at reefs throughout the Keys, and has even become a well-attended event. Apparently other species take a cue from the coral because sponges, brittle stars, gorgonians, and Christmas tree worms are known to spawn at the same time.
Dive shops throughout the Keys offer night dive trips to observe the coral spawn. Although the activity is geared around the August full moon, it can vary according to the reef and the species.
Elkhorn and staghorn branching corals tend to spawn with the full moon while star corals spawn eight days later.