Sex on the Reef
The International Year of the Reef 2008 is a worldwide campaign to raise awareness of the value and importance of coral reefs and threats to their sustainability, and to motivate people to take action to protect them. To that end, over the next year, articles about coral reefs will be featured regularly in this magazine.
On unsuspecting nights, sometime after the August full moon and sometime after the sun goes down, our crystal clear waters turn murky from a lively display of exploding eggs and sperm from corals in an undersea love fest. This phenomenon is known as coral reef spawning. Although some corals often reproduce asexually by dividing and creating an exact replica of themselves, only once a year corals will reproduce sexually by releasing both eggs and sperm into the water column. This exhibition lasts less than an hour and can be seen while snorkelling, but is best seen while scuba diving.
This event was first officially recognized in 1981, but many questions remain unanswered. Experts once believed most of the corals would reproduce by brooding larvae inside the polyps, and then releasing the larvae onto the surrounding reef. Now it is better understood that many corals will reproduce by “broadcasting” eggs and sperm into the water for external fertilization. While coral spawning is known to occur around the world, the timing of the event is made more unpredictable because not all coral species spawn at the same time. New studies have found that corals have photoreceptors sensitive to the blue portion of lunar irradiance; in other words, the full moon most likely has something to do with the event. Enough studies have been conducted now throughout the Caribbean to pinpoint the timing of the spawning event down to about a week. (See the accompanying chart for this year’s predictions).
The evolutionary rationale behind this particular method of reproduction is that the greater the number of eggs floating around the ocean, the better chance of survival, especially since many reef and pelagic predators feed on the spawn. The ocean currents also take many of the fertilized eggs to new areas for colonization and increase the distribution of genetically different coral species.
For those who enjoy night diving, coral spawning is a dramatic display of nature to witness, made even more exciting by the number of other organisms that spawn at the same time, such as sponges, brittle stars and Christmas tree worms. There is also a myriad of reef and pelagic fishes that swarm to the area to feed on the spawn. So if you are out diving a week or so after the August full moon, keep an eye out for spawning corals. If you do happen to see this event, please give the Conservation & Fisheries Department a call at 284-494-3429; we are keeping records to ensure even better predictions in the future.
