Several species of coral polyps, the tiny invertebrates whose fragile colonies build the reefs of the Virgin Islands, are now known to spawn on the same night each year, according to marine photojournalist Jesse Cancelmo. Local divers led by Chris Sawyer will contribute their observations of reef spawning when the annual occurrence takes place Wednesday, and experienced night divers are being sought to volunteer.
Cancelmo wrote in a recent article for Dive Training Magazine that the mass spawning phenomenon was first reported in scientific journals in 1984 by researchers at Australia's Great Barrier Reef. Six years later, he said, a similar mass spawning was noted by a group of night divers from Texas in the Gulf of Mexico.
"The mass coral spawning phenomenon," Cancelmo said, "is a subject of great interest to marine scientists and researchers. A better understanding of coral reproduction may provide clues for developing methods to repair and rejuvenate damaged reefs."
In 1995, organizer Jim Hart of Oceanographic Expeditions invited sport divers to join scientists and oceanographers in an effort they named Project Reef Spawn.
"The most important information that we can obtain from divers," he wrote on the project's data collection sheet, "is short written summaries, video footage or photographs that describe their observations of the spawning. Your data is very helpful to scientists and oceanographers trying to unravel the mysteries of this event."
Armed with cameras and Project Reef Spawn data collection sheets, experienced night divers assembled by local dive operator Sawyer have recorded details during each of the past five spawning events.
Based on his past experience, he expects conditions this year to be optimal from shortly after sunset on Wednesday, August 23, until roughly 10 p.m.
"That," according to Sawyer, "is when the water temperature, light levels and the lunar cycle cue many corals to spawn simultaneously. All at once, both star and brain coral heads will begin releasing many thousands of orange or pink BB-sized sperm and egg packets into the water.
"We've also seen tube sponges spawning along with the corals. We'll dive repeatedly in buddy teams and record our observations for the Project Reef Spawn scientists."
In the past, Sawyer has collected spawning data at reefs between St. Thomas and St. John, but he said all reefs in the Virgin Islands are likely to respond in kind.
Researchers recognize mass simultaneous spawning as an effective reproductive strategy that overwhelms hungry predators that might otherwise eat all of the tiny coral eggs.
Most egg packets don't get far before being gobbled up by eager brittle stars, bristle worms, crabs and reef fish. Those packets that survive the nocturnal feeding frenzy drift out of harm's way in the tropical current, eventually settling in a new location to build a separate coral colony.
Interested in adding your firsthand observations to Project Reef Spawn? Coral Spawning Data Forms are available on St. Thomas from the Chris Sawyer Diving Center at 777-7804. Further information about Project Reef Spawn is available from project coordinator Hart at (504) 488-1573 or e-mail [email protected].