Coral Spawning on the Great Barrier Reef

What is coral spawning?

Coral spawning is a reproductive event in which coral polyps release bundles containing eggs and sperm into the water. When the bundles meet, fertilisation can take place. The eggs then develop into tiny, free-swimming coral larvae called planulae.

The larvae drift with ocean currents for several days or weeks before some settle on a suitable surface and begin growing into new coral colonies.

When does coral spawning happen?

On the Great Barrier Reef, coral spawning usually takes place at night in the period following the full moons in October, November or December. The timing varies between reef locations and species and depends on environmental cues including seasonal water temperatures and the lunar cycle.

There isn’t one set date for the whole Reef, and exact dates can’t be guaranteed. For general information, visit the Reef Authority’s coral spawning page. For local Whitsundays updates, check Reef Catchments’ latest articles.

How do corals know when to spawn?

Corals respond to a combination of environmental cues. Seasonal warming and the lunar cycle help signal when conditions may be right, while factors such as tides and daylight can also play a part.

Spawning at the same time gives eggs and sperm from nearby colonies a better chance of meeting. It usually happens at night, when there are fewer active predators feeding on the eggs and sperm.

The importance of coral spawning

Spawning produces the next generation of corals and helps maintain genetic diversity across the Reef. After fertilisation, some larvae settle and grow into new colonies.

Corals that survive challenging conditions may carry traits that help future generations cope with stress. However, spawning takes a lot of energy, and corals still recovering from impacts such as bleaching may not be healthy enough to reproduce.

What might you see on a reef trip?

Explore doesn’t offer overnight trips specifically to witness coral spawning. The event happens at night, but in the days afterwards you may see slicks of spawn or developing larvae on the water’s surface.

These slicks can appear pink, yellow, orange or pale in colour, and their visibility depends on conditions such as wind and currents. A surface slick can be difficult to identify by colour alone, so sightings aren’t guaranteed.

Planning a reef trip? See Explore’s Great Barrier Reef experiences from Airlie Beach and Hamilton Island reef tours.

Does bleached coral mean the Reef is dead?

Bleaching doesn’t automatically mean a coral is dead. When corals are stressed, they can expel the microscopic algae that live in their tissues and provide much of their colour and energy. Without the algae, the coral’s white skeleton becomes visible.

Bleached coral is stressed and may recover if conditions improve. If the stress continues or is severe, the coral can die. Bleaching can also affect a coral’s growth and ability to reproduce.

Help researchers keep track of sightings

If you see what you think may be coral spawn, you can share your sighting through the Reef Authority’s Eye on the Reef app or sightings network. Photos and location information can help researchers and managers learn more about Reef health and coral reproduction.