What natural event releases coral eggs and sperm across the Great Barrier Reef?

Mass coral spawning releases coral eggs and sperm across the Great Barrier Reef.

During this spectacular reproductive event, many coral colonies release bundles of eggs and sperm into the water at roughly the same time. The synchronised release increases the chance that reproductive cells will meet, helping corals reproduce successfully across large areas of reef.

Great Barrier Reef spawning is commonly associated with the warmer months and often occurs after particular lunar cues, especially around November. The exact timing varies among coral species, locations and environmental conditions, so it is not a single event occurring on one fixed night everywhere. This is why “mass spawning” is more precise than simply calling it a coral bloom.

After fertilisation, coral larvae drift with currents before settling on suitable surfaces and developing into new colonies. Spawning differs from coral bleaching: bleaching is a stress response in which corals lose symbiotic algae, whereas spawning is a natural reproductive process. The event is scientifically important because it reveals how reef-building corals renew populations and maintain genetic diversity.