Each year sometime around November a synchronised coral spawning takes place on the Great Barrier Reef. If you’re lucky enough to be visiting during this time, it is quite a spectacular event that attracts scuba divers and snorkelers from across the globe. As coral spawning is linked to the moon and water temperatures, it’s hard to predict exactly when this mass reproduction will happen.
Likened to underwater fireworks, coral spawning on the Great Barrier Reef involves colonies and species of coral polyps simultaneously releasing tiny egg and sperm bundles from their gut cavity into the water.
This is how last year’s coral spawning played out – it was pretty spectacular!
Video by Calypso Productions
By expelling the eggs and sperm at the same time, the coral increases the likelihood that fertilisation will take place, populating the Great Barrier Reef for future generations.
The mass spawning occurs after a full moon and only after rising water temperatures have stimulated maturation within the adult coral. The day, tide and salinity levels also appear to be factors in deciding when the event will happen.
The spawning lasts between a few days and a week. This is because different species release their eggs and sperm on different days to prevent hybrids from being produced.
The phenomenon — which only happens at night — results in a cascade of clouds of red, yellow and orange bundles which rise slowly to the surface where the process of fertilisation begins.
While spawning takes place on a large scale, it doesn’t happen across the entire Great Barrier Reef all at once.
Instead, the time of year that corals spawn depends on their location. Those on inshore reefs usually start spawning one to six nights after the first full moon in October, whereas those in outer reefs spawn during November or December.
When an egg is fertilised by a sperm it develops into coral larva called a planula that floats around in the water for several days or weeks before settling on the ocean floor. After the planula has settled in a particular area it starts to bud and the coral colony develops.
The mass spawning also provides ready food for other marine creatures, particularly nocturnal animals such as plankton and some fish species.
Local dive operators are well-versed on this annual phenomena and usually plan their trips to the reef to coincide with the best viewing opportunities. Ask our Adventure Desk team to book your spot for this wonderful event on the Great Barrier Reef!