Every year, the Great Barrier Reef puts on one of its most spectacular natural displays over three nights.
Known as coral spawning, this underwater event sees millions of coral eggs and sperm released into the water in a synchronised burst of activity. In the water, tiny 'bundles' of coral eggs and sperm - which look like tiny balls - are released by coral colonies and float up to the water's surface.
Often called 'sex on the Reef', coral spawning usually occurs on reefs one to six nights after the October, November and December full moons. Corals on outer shelf reefs usually spawn one lunar month later than inshore corals. The timing varies across the Reef and is influenced by factors including water temperature and the lunar cycle.
It's one of the most important times for coral on the Great Barrier Reef, providing hope for a resilient future for corals on the reef.
How does coral spawning work?
During spawning, coral colonies release bundles containing eggs and sperm into the water. When the eggs are fertilised, they develop into tiny, free-swimming larvae called planulae.
These larvae drift with ocean currents for several days or weeks before settling on a suitable surface on the reef, where they can grow into new coral colonies.
This process helps replenish coral populations, supports genetic diversity and gives the Reef an opportunity to recover from damage.
Corals aren't the only marine life getting in on the action, either. Other marine species, including sponges, echinoderms, molluscs and other invertebrates, can also engage in broadcast spawning around the same time. It also follows turtle mating and the spawning of some reef fish, occurring around the time of coral spawning.
Can bleached corals spawn?
Coral spawning is an energy-intensive process, and corals affected by bleaching or other pressures may not be healthy enough to reproduce.
Coral spawning is essential for maintaining healthy coral reef ecosystems. By producing new generations of corals, it helps maintain coral populations. This diversity gives future generations a better chance of adapting to changing environmental conditions.
Genetic diversity is an important part of a healthy, resilient reef. The more variation within coral populations, the greater the chance that some corals will have traits that help them cope with changing conditions.
Reef Authority management actions help protect the conditions corals need to survive and reproduce. These include addressing poor water quality, tackling illegal fishing, and reducing pressures like Crown-of-thorns starfish.
Help keep an eye on the Reef
Coral spawning provides scientists and Reef managers with valuable information about coral health and reproductive capacity.
Whether you witness spawning underwater at night or spot a slick of spawn on the water's surface, you can help by reporting your sighting through the Eye on the Reef app. Include photos where possible.
Every sighting helps build a better picture of what is happening across the Great Barrier Reef and supports management decisions to protect its future.
Coral spawning facts
- The released bundles of coral eggs and sperm can be colourful, appearing as clouds of pink, yellow, and orange, resembling an underwater snowstorm.
- Coral spawning usually happens at night, which helps protect the vulnerable eggs and sperm from predators.
- Using safety in numbers, many other marine species will spawn alongside the corals. Invertebrates, sponges and more will often spawn at the same time.
- After fertilization, the eggs develop into tiny larvae called planulae, which float in the water for several days or weeks before settling on a suitable substrate.
- The corals that successfully spawn after bleaching events carry genetic traits that can help future generations withstand mounting pressures from climate change, poor-water quality and other threats.
- Coral spawning is the most significant event to preserve the future health and resilience of coral cover on the Great Barrier Reef.
