Everything you need to know about coral spawning on the Great Barrier Reef

Guide

By Sarah Campbell

Coral spawning 2024 | What is coral spawning? | When does it happen? | How to see it

Each year, around the full moon in November, the world’s largest synchronised coral spawning event happens along the Great Barrier Reef — described by Sir David Attenborough as ‘one of the greatest of all natural spectacles’..

But what exactly is this gigantic underwater snowstorm, and how can you go and experience it first-hand?

Coral spawning on the Great Barrier Reef 2024

22 November 2024: Ever heard of Coral IVF? To help this year’s coral spawning produce more coral babies, tourism operators and the local Reef industry have worked through the night to capture millions of coral eggs and sperm.

Bundled into specially designed floating larval pools for up to a week before being placed onto reefs, this initiative will greatly support the Reef’s natural regeneration process as scientists estimate that Coral IVF boosts successful coral fertilisation rates by 100-fold — raising the chances of one in a million in natural settings to one in 10,000.

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By combining the tourism and marine industry’s leadership, vessels, local expertise and people power, we’re aiming to achieve reef restoration on a much larger scale than researchers alone could accomplish. This is truly a powerful partnership.

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Anna Marsden

Great Barrier Reef Foundation Managing Director

What is coral spawning?

Coral spawning on the Great Barrier Reef 2024

Coral spawning really is the biggest reproduction show on Earth. And as inquisitive humans, we love to watch.

Once a year corals simultaneously release eggs and sperm bundles (spawn) into the water. These bundles then rise slowly to the surface where the fertilisation process begins. If successful, the fertilised eggs will settle on the ocean floor, eventually developing into coral.

The spawning can last a couple of hours or a few days.

With the health of the Reef continuing to make headlines, the interest in coral spawning has never been so high.

When does coral spawning happen?

Well, see that’s the interesting thing. No-one knows exactly.

Sure, marine scientists can predict a rough timeframe, but they’re never going to put their house on an exact time and date.

Scientists at Townsville’s James Cook University only discovered the coral spawning phenomenon for the first time in 1981, so while research around it has developed since then, it’s still impossible to say exactly when it will occur.

Generally, coral spawning takes place between November and December in the northern Great Barrier Reef.

“Coral spawning generally happens two to six days after a full moon in November when the water temperature has been over 27 degrees Celsius for a month prior," says Marine biologist and Reef Teach Master Reef Guide Gareth Phillips.

“And while we are somewhat able to predict a timeframe for when it might happen, so much about this annual event is still a mystery, for example what exactly triggers the synchronized release. However, spawning happens later on the southern or outer reaches of the Reef."

How do environmental factors affect coral spawning?

There are several environmental factors that affect when coral are likely to spawn:

The ocean temperatures must be 26 degrees or above for the month before for the eggs to mature enough.
The coral will reproduce three to six nights after the full moon in November or December (in the northern Reef) when there’s less tidal movement.
Spawning is also most likely to take place at least three hours after sunset when all plankton feeders are sleeping, giving eggs more time to settle into the safety of the Reef and ensure a higher chance of survival.

What's the best way to see coral spawning?

Coral spawning can occur between Heron Island to the south, and Port Douglas to the north, across a distance of 1000kms.

If you want to be among the action, your best chance of seeing coral spawning is by heading out on a dive boat from Cairns.

Operators like Tusa Dive, Divers Den and Pro Dive all offer night trips out to the Reef for coral spawning. These trips are suitable for divers, snorkellers or just keen observers.

After the experience of a nighttime visit to the Reef, extend your stay in Cairns to see some of the famous dive sites during the day.

You can also take a four day/three night liveaboard boat out of Townsville with Adrenalin Snorkel and Dive. You’ll enjoy up to three night dives to see the spawning, as well as having the chance to visit other sites during the day like Lodestone Reef and Keeper Reef.

While the Whitsundays region isn’t renowned for its coral spawning viewing opportunities, there’s always the chance it could be the place to see it this season. Charter your own yacht to head out and see if you can witness the magic.

Just by visiting the Reef you’re helping to contribute to its long-term health.

A portion of the cost of visiting the Reef with a tour operator goes to the Great Barrier Marine Park Authority, who manages the Reef and its conservation.

You can even see it on land

Rather not go on a boat at all?

You can see the spawning from an island resort on the Reef. One of your best opportunities is on Lady Elliot Island.

Though they don’t run specific coral spawning night dives, if you’re on the island during the event it’s easy to see the spawning.

If the tide’s high enough you can see it night snorkelling in the lagoon. Or keep dry, thanks to a night time glass bottom boat tour during the spawning. There’s also night diving available just offshore from the resort.

Learn more about the state of the reef and the ongoing efforts to keep it thriving in Great Barrier Reef myths, busted by marine biologist Russel Hore.