Annual coral spawning a spectacular sight for divers

A diver inspects a spawning coral on Thursday night. – PHOTO: LOIS HATCHER, OCEAN FRONTIERS

Over a couple of nights every September, a few days after the full moon, the corals of the Cayman Islands burst into life as their annual spawning gets under way. Last week, divers got to experience the spawning show, which lasts about 20 to 30 minutes.

The spawning of hard corals across all three islands commenced at 10:01 p.m. on Thursday, Sept. 22, six days after the full moon.

Corals – living creatures that are the mainstay of any reef – are stationery creatures, making reproduction a rather difficult task. The corals are “broadcast spawners” and reproduce by spewing huge numbers of male and female gametes into the water.

The gametes latch onto the opposite sex and the cycle begins again. There is a very short window during which divers can observe this natural spectacle.

The primary species of corals that released spawn were the Mountainous Star Coral (Montastraea faveolata) and the Lobed Star Coral (Montastraea annularis).

Steve Broadbelt, owner of Ocean Frontiers dive shop, and Dr. Alexander Mustard, first discovered and documented this natural phenomenon in the Cayman Islands in 2002.

Ocean Frontiers in East End took divers down to view the spawning, having calculated, for 14 years running, exactly when the spawning is most likely to take place.

A coral releases its gametes into the ocean Thursday night as the annual mass coral spawning got under way. Divers were treated to the natural spectacle, which lasts 20-30 minutes, at sites around Grand Cayman last week. – PHOTO: LOIS HATCHER, OCEAN FRONTIERS
A coral releases its gametes into the ocean Thursday night as the annual mass coral spawning got under way. Divers were treated to the natural spectacle, which lasts 20-30 minutes, at sites around Grand Cayman last week. – PHOTO: LOIS HATCHER, OCEAN FRONTIERS

Two full dive boats headed out on Thursday for the peak of coral spawning, each visiting a different site, Playing Field Reef and Fantasea Land. Despite the three-mile distance between the dive sites, both reefs spawned in spectacular fashion at the same time.

“Even though I have 14 years’ experience in coral spawning, I still get very anxious before the dives,” Mr. Broadbelt said. “On Thursday, we had 24 divers between two boats and they were all counting on me to pinpoint that window, and we nailed it.”

The simultaneous release of spawn of Mountainous and Lobed Star Corals are the most spectacular to watch and a favorite with divers.

Mr. Broadbelt said, “What makes these dives special is that you have to wait all year to witness a 20-minute marvel of nature. If you didn’t quite get the photo, then you have to wait another 365 days before you can try again.”

Friday night resulted in a repeat performance to finish off the corals reproduction cycle for another year.

Approximately 70 percent of the individual colonies spawned late Thursday night and the remaining spawned on Friday.

But the highlight of Friday night’s spawning was to witness the Grooved Brain Coral (Diploria labyrinthiformis) and Symmetrical Brain Coral (Diploria strigosa), which display a semi-synchronous spawn release with a chain reaction, domino effect order of release, Mr. Broadbelt explained.

“Many of our divers planned their entire vacation around the coral spawning, flying down to Cayman specifically for these dates. We are able to accurately plan these dives years in advance with published moon, tide and sunset data.”

Next year the coral spawning will be on Sept. 12 and 13.

Before each of the coral spawning night dives, Mr. Broadbelt conducts a 30-minute presentation explaining how and when the coral spawn. Detailed images and video clips in the presentation help the divers to identify which corals are going to spawn that night and which are not.

After the release, the bundles of spawn swell in size and rise through the water to the surface. They then dissolve and fertilize. Less than 1 percent will land on a suitable substrate on the reef and an even smaller percentage will actually develop into coral colonies. The rest of the spawn simply becomes part of the food chain.

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