FLORIDA KEYS -- Every year, patrons of Florida Keys dive and snorkel shops play a guessing game. Locals and visitors alike try to guess the date and time of the annual coral spawn — sometimes nicknamed "sex on the reef" — on North America's only living coral barrier reef, which parallels the island chain.
  Corals were created with a method of reproduction called "broadcast spawning." The immobile animals send their eggs and sperm into the water in massive quantities. When egg and sperm unite, the resulting larval-stage "planula" swims to the surface to drift in the current and grow. After some time — two days to two months — the planula settles to the bottom where it grows into a polyp. The polyp grows into a coral head by asexual budding that creates new polyps.

Key to the successful creation of the next generation is corals in a given location broadcasting their eggs and sperm cells simultaneously. So the great mystery that has challenged researchers is: “How do brainless, stationary, uncommunicative corals know exactly when to broadcast their spawn?”

Thanks to the pioneering research of Dr. Alina Szmant of the University of North Carolina Wilmington, and ongoing studies by Dr. Margaret Miller of the National Oceanographic and Atmospheric Administration's National Marine Fisheries Service, the mystery surrounding the coral spawn gradually is being solved.

Szmant's observations have shown that Caribbean corals usually spawn around the mid to late August full moon.

The generally accepted schedule is for branching corals (e.g., finger, staghorn and elkhorn corals) in the Keys to spawn three to five days after the full moon, about two hours after sunset. Star and boulder corals spawn six to eight days after the August full moon, about three hours after sunset.

Guessing which night and at what time the corals will spawn is not an exact science, but professional researchers and amateur observers usually have a pretty good chance of seeing the action within a five-day span.

This year, the full moon is scheduled for Aug. 28. Therefore, divers and snorkelers visiting the Florida Keys National Marine Sanctuary should be able to catch a glimpse of one of nature's great mysteries in early September and a number of Keys dive shops offer up special evening excursions for voyeurs of the spectacle many have described as an "upside-down snowstorm."

For more details on Keys accommodations and links to dive shops in the region, examine www.fla-keys.com