NOAA's Reporter's Coral Reef Tip Sheet
August 11, 1997 - Week 32

If you happen to be diving between 9:00 and 11:00 at night in the Flower Garden Banks National Marine Sanctuary 100 miles off the Texas/Louisiana coast on August 25, you are likely to witness one of the most amazing spectacles nature has to offer -- coral sex. For two hours each year, eight evenings after the August full moon, these tiny animals erupt in a reproductive frenzy that looks like an upside-down snowstorm. It's mass coral spawning -- a vital part of the life cycle of many reef-building corals.

First witnessed by sport divers in Texas in the early 1990's, the mass spawning has become a tourist attraction for adventurous divers, a business endeavor for ecotourism operators, and a field of study for some coral reef scientists. Mass spawning events also take place in the Florida Keys National Marine Sanctuary (between August 18 and 26 this year), but predicting the exact time is not always as easy as it is in Flower Garden Banks. On reefs in the Pacific Ocean, Indian Ocean, and Red Sea, mass spawning occurs during different times of the year.

During a mass spawning event, some coral species release millions of BB-sized bundles into the water column, each containing eggs and sperm. Other species release just eggs, or just sperm. Within minutes, this reproductive material floats to the surface, forming a surface slick with a mildly sweet aroma. It is there that the eggs are fertilized. The embryos quickly develop into larval forms called planulae that drift for several days or weeks before settling onto the ocean bottom. If water and bottom conditions are right, a few lucky larvae form solitary coral polyps; pea-sized cousins of jellyfish attached to the bottom with their tentacles extended to capture food and compete for space. These polyps divide asexually, forming colonies of genetically identical individuals. Shaped like large boulders, brains, or antlers, some colonies exceed the size of the average living room after a few hundred years of growth.

Scientists are still trying to determine what environmental cues the corals use to synchronize their spawning activity. It is clear that the moon plays a part. The species that participate in the mass spawning release their gametes during the last quarter of the moon - the half moon following the full moon - and only after the water temperature has reached its peak for the year. In places with warm water year round, spawning seems to be less precise and may take place over more than one month.

Mysteries still remain about coral reproduction and early life history. Scientists are studying whether different species can form hybrids by cross fertilizing, whether individual colonies can self-fertilize, what effect environmental pollution has on larval and juvenile survival, whether coral spawning is related to the overall health of a coral reef, and whether corals can be raised in captivity for possible use in restoring damaged coral reefs. They are also trying to figure out why other animals, such as brittle stars, sea cucumbers, worms, and some fish spawn about the same time as corals. Their findings may dramatically affect the future of coral reefs, the landforms they protect, and the people who depend on them.

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FOR MORE INFORMATION ON CORAL SPAWNING IN THE FLOWER GARDEN BANKS NMS OR FLORIDA KEYS NMS PLEASE CONTACT: