Annual coral spawning begins on Great Barrier Reef

By Australian Geographic 28 November 2018
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CORAL POLYPS have begun simultaneously releasing eggs and sperm bundles for external fertilisation, marking a beginning to the annual spawning event for 2018.

It began last night on Moore Reef, directly off the coast of Cairns, and scientists believe the spawning will continue today and tomorrow.

“We had patchy spawning last night with the soft corals and we anticipate the Acropora, Montipora and other stony corals will mass spawn on Thursday which is when it feels like you are swimming through an upside down snow storm,” said marine biologist Stuart Ireland, who captured the video.

“The spawn varies from small to tiny pink and mauve balls which represent either eggs or bundled egg and sperm masses, while cloud-like white slicks or ‘smokers’ represent individual male colonies.”

Coral spawning, now regarded as a natural wonder, was first discovered back in 1981 by a Jame Cook University research team. Stuart has been documenting coral spawning since 1996.

The event is difficult to predict and so being at the right place at the right time is key. What is known is that the phenomenon only happens at night, after rising water temperatures have stimulated the maturation of gametes (the egg and sperm) within the polyps. And they usually occur over several days to just over a week after a full moon.

Thus far, the largest synchronised spawning events recorded have occurred on Queensland’s Great Barrier Reef and in Western Australia’s reefs. Large-scale spawning events on Western Australia’s reefs tend to occur in autumn, with smaller but significant events also recorded in spring, while large events on the Great Barrier Reef appear to take place only in late spring or early summer.