Great Barrier Reef bursts to life in nature’s most spectacular yearly event

Coral spawning

Jamie Jansen

Journalist

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The annual mass coral spawning causes an underwater snowstorm.

One of nature's most awe-inspiring events has started; the spectacular and mysterious mass coral spawning.

Once a year, following a full moon in November, the Great Barrier Reef turns into an underwater spectacle resembling the inside of a snowglobe.

On cues from the lunar cycle and the water temperature, entire colonies of coral reefs simultaneously release their tiny egg and sperm bundles into the ocean for external fertilisation.

This causes an underwater snowstorm with billions of colourful flakes cascading in white, yellow, red, and orange.

According to Jenny Edmondson, marine biologist and owner of Wavelength Port Douglas, the spawning was revived yesterday night and tonight on the outer reef off Port Douglas.

Simultaneous reproduction

Coral spawning is an annual mass event where corals simultaneously reproduce.

“Corals release their eggs and sperm into the water,” Ms Edmondson explained.

“They make their way up to the surface and hopefully make larvae which then move on the currents until they settle out some time later on the ocean floor and some survive to make new baby corals.

“The reef looks like it’s upside down snowing with ‘snow’ being the egg and sperm packets streaming from the coral mouths up to the surface.

“There is then a frenzy of worms and fish trying to eat as much as they can, it's like a fiesta!”

The perfect timing

Coral spawning generally happens two to six days after a full moon in November when water temperatures have risen enough to stimulate the maturation of the egg and sperm bundles.

However, there remains a lot of mystery around the exact dates of when the coral spawning happens.

It only happens at night once most plankton feeders are sleeping to give the eggs a greater chance at survival.

“It was only discovered about 30 years ago that most of the hard corals spawn on one or 2 nights a year,” Ms Edmondson said. “It’s a dark science trying to predict when it’s going to happen.

“These days it’s realised that there’s a bit of stagnation with different species spawning at different times after darkness falls presumably to get better success in the right species gametes meeting up at the surface.

“It is hard to say how long it lasts, approximately 5 to 7 hours over 3 nights after the full moon in November or December but nobody wants to be pinned down.”

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