One-by-one, the silent explosions begin, like an underwater fireworks display.
Tiny pink balls rise like bubbles, fizzing from the coral heads and accumulating in thick clouds in the water column.
This is how a reef reproduces.
For most of their lives, corals appear as inert and impassive as rocks.
Once a year, just after the September full moon, in response to some unfathomable trigger, they come to life in spectacular fashion.
For the scuba divers witnessing the phenomenon, it is like swimming in a snow globe.
Entire coral colonies simultaneously send bundles of sperm and eggs into the water. These colourful gametes mix together and some become coral larva.
With luck, a small fraction 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.
On Tuesday night, 8 Sept., dive operator Ocean Frontiers, which has become a specialist at predicting the timing of the annual event, took 45 divers to three sites around the island to view the spectacle.
There are 19 different types of hard coral that spawn throughout September, but dive shop owner Steve Broadbelt says the lobed star, mountainous star, and symmetrical brain corals are the easiest to predict and the most spectacular to watch.
“Ocean Frontiers has been successfully observing coral spawning since 2002, when myself and Dr. Alex Mustard finally figured out the timing formula after a few years of getting it wrong,” said Broadbelt.
Video by Tom Williamson:
The event has become a bucket-list dive for scuba enthusiasts, and Broadbelt said it was encouraging to fill three boats entirely with local divers.
“As divers are ‘stuck here’ and unable to travel, they are seeking out adventures locally, and perhaps discovering and appreciating that they live in one of the best places in the world to go scuba diving,” he said.
“Never before have we taken 45 divers night diving on the same evening. The highlight for me was that all divers from all three of our boats witnessed the spawning and experienced a night dive they will always remember.”