Witnessing one of the great mysteries of the reef, Coral Spawning is one of the most rewarding experiences that a diver can witness in his/her Scuba lifetime. One of the most unpredictable phenomenons that occurs only once each year and that too at night, makes the event all the more special.

Corals use several reproductive strategies from broadcasting their eggs and sperm to brooding (Corals that do not broadcast their eggs).  About 75% of coral species are broadcasters and once a year in a synchronized event, all coral in the reef release their gametes into the waters, dispersing several million eggs over 2-3 days believed to maximize the chances of fertilization, and at the same time overwhelm predators with more food than they can eat. The cues that guide the release are highly complex and still not fully understood today. But marine biologists believe it is a combination of factors such as lunar changes, water temperature, sunset time, and possibly chemical signaling.

The gametes fuse during fertilization to form a microscopic larva called a Planula, that float to the surface where it embarks on a voyage that can last for months and carry it hundreds of miles from its origin, past filter feeders, fish, and predators until it finally finds a suitable substrate where it will begin to calcify and form coral.

In Australia’s Great Barrier Reef, coral spawning occurs usually in November. Corals need exactly the right conditions (sea temperature, tides, time of day) to spawn, and mass spawning usually occurs 4-6 nights after the full moon in November. This is a huge event for divers who often staying of liveaboards dive steadily each night during this period in the hopes of catching a glimpse of the spawning. The first signs is the sight of colored bundles of eggs inside female polyps being squeezed out through the mouths of the polyps and released hundreds each minutes filling the Reef with eggs. This sight has often been compared by divers as an “upside-down snowstorm.” Next the male polyps produce clouds of sperm that clouds the waters up rapidly ruining visibility. Divers therefore have a narrow window in which to witness this spectacle.

Divers hoping to witness spawning should choose a dive site that has plenty of coral, and relatively shallow to maximize your bottom time. Look carefully at the coral for swollen polyps with pink eggs inside them as this is a sign that they are ready to spawn. Usually a few hours after sunset is the best time to spot coral spawning.

As mentioned above the Great Barrier Reef coral is said to spawn each year in November. In Bonaire which is an excellent place to witness coral spawning due to the proximity of the reefs from the shore, and abundance of coral species, spawning takes place in September and/or October, and often have predicted schedules posted on their tourism website. In the Caribbean coral spawning occurs usually in the first week of August, and schedules are usually posted on each destinations dive websites.

photos by: Orang Asli, Brittanie Shey