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Coral spawning

By on November 28th, 2018

Every year on coral reefs around the world all coral species spawn en masse on the same night.

It’s been described like an underwater snowstorm, as if you were swimming through a snow globe. There are various colours, and they can form clouds of white, pink, red, orange or yellow dots, floating all around.

This phenomenon was only discovered in 1981, so there’s still so much to learn about it. There’s currently a team of marine biologists studying coral and spawning at the National Sea Simulator at the AIMS facility just north of the Whitsundays. Through their research, they hope to learn more about coral, bleaching, spawning, growth, and health, to help better protect the Great Barrier Reef.

There’s even a current coral spawning project being undertaken that has been dubbed ‘IVF for the Great Barrier Reef”!

What is coral spawn?

Photo: www.secore.orgCoral spawn is coral eggs and sperm! Corals are living creatures, not plants, and they reproduce by making ‘babies’. Most coral are hermaphrodites, so they produce both male and female reproductive cells.

The corals simultaneously release masses of eggs and sperm into the water. Hopefully the eggs and sperm find each other to form larvae, and create lots of new little coral babies!

Once fertilised, these little coral larvae are called ‘planula’. Planula will float around for days or sometimes even weeks, until they reach a suitable location to establish themselves.

Coral spawn is often confused with plankton blooms called trichodesmium. Trichodesmium, also called sea sawdust, is normally a red/brown color, floats on or near the surface and is often found in large streams. It is a natural phenomenon caused when the water is warm and conditions calm.

Coral spawn - The Great Barrier Reef on FBWhen does coral spawning occur?

On the northern parts of Queensland’s Great Barrier Reef, where the Whitsundays area, it usually occurs in late spring or early summer. Most commonly coral spawning happens in November or December, but it has occurred between October and January.

In 2018, spawning was recorded on reefs in the Whitsundays on 27 – 28 November 2018.

Coral spawning usually only happens once a year. In rare years, when conditions are just right, coral may spawn more than once, in two consecutive months!

It occurs when the water temperature is just right, 26 degrees or warmer for a whole month, and follows the phases of the moon. Spawning usually happens 3-6 nights after the full moon, when there is little tidal movement.

Coral spawning always happens at night, usually around 3 hours after sunset, so specialised night diving equipment is needed to witness the spectacle. This is because by this time all the sea creatures that feed on plankton are asleep, and the coral spawn has more time to settle on the reef without being eaten.

coral about to spawn - Philip MercurioHow can you see coral spawning?

As if the uncertainty surrounding the month of coral spawning weren’t vague enough, it’s also hard to predict which day it will happen. There are very few coral spawning tours offered for tourists, and no guarantees can be given that it will actually occur.

Signs of spawning aren’t visible until about 20 – 30 minutes before it actually happens, when the egg can be seen rising through the coral polyp as it makes it’s way towards release.

Night dives or snorkels should only be conducted by experienced divers on guided tours. Whitsunday Escape does not recommend snorkelling at night.

Coral spawning videos

2018 Coral Spawning Video in the Whitsundays

Update: Local Marine Biologist Johnny Gaskell has filmed the spawning event in the Whitsundays. He and the team from Daydream Island report that the coral did in fact spawn over 2 nights, 27 – 28 November, and they were lucky enough to witness it on both nights just off the coast of Daydream Island itself. Magic!

 

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