Illuminated by the moody glow of a dozen torchlights, a group of divers hovers over the reef.
The distinctive antler-like shape of a large staghorn formation emerges from the gloom. An octopus squirts between coral heads. Bloodworms swarm in the torch beams.
It’s just after 10pm on a reef off East End known as Fantasea Land. It is an unusual time to be in the water, but the group from Ocean Frontiers dive shop is here for a reason. One of the most iconic displays in nature is about to begin.
The spectacle starts slowly at first.
Tiny pink bubbles fizz from a large head of mountainous star coral, so named because of the peaks and valleys that cover its stony surface. Then it erupts, and bundles of gametes gush into the water column, drifting upwards like a snowstorm in reverse.
Soon the entire reef is exploding.
Across Cayman’s reefs, the same phenomenon occurs almost simultaneously. Within the space of 20 minutes, six or seven nights after the September full moon, almost every hard coral in Cayman’s reef system spontaneously reproduces.
This is how these stationary creatures, sometimes referred to as living underwater cities, rebuild themselves.
Entire coral colonies simultaneously send bundles of sperm and eggs into the water. The colourful flakes, known as gametes, mix together in an underwater blizzard. Some join together to become coral larva.
With luck, a fraction of one percent of them will survive the gauntlet of predators and drop to the ocean floor where, depending on the conditions, they may begin to form new coral colonies, growing at the infinitesimally slow rate of a centimetre per year.
The chance to see the moment of conception for organisms that can take millions of years to grow into the spectacular coral reefs that make up Cayman’s underwater world is something that people come from far and wide to see.
Steve Broadbelt, of Ocean Frontiers, says the shop’s annual coral spawning night dives are often sold out months in advance.
“It is something that is on the bucket list for a lot of divers,” he said, “because it is the chance to see something that not many people get to see.
“This is about being in sync with nature. Being in the right place at the right time. It happens once a year for 20 minutes and if you miss it, that’s it for another year.”
Over the last 20 years, Broadbelt and his dive buddy, underwater photographer Alex Mustard, have got the timing down to a fine art.
Still, Broadbelt feels the pressure.
“I get anxious every time because this is a natural phenomenon,” he said. “People have timed their trips to Cayman to come and see it, but there are no absolute guarantees. We have a good system to predict when it will happen, but there is always a chance that we will see nothing. For me it is always a relief when it happens.”