2020 Coral Spawning event: The World’s Biggest Reproductive Show

This weekend (4-6 December 2020), corals in the Great Barrier Reef released trillions of egg and sperm into the ocean in a synchronised effort to reproduce. It’s safe to say, the 2020 coral spawning event went OFF. Often described as a gigantic underwater snowstorm, this natural phenomenon happens on only a few nights each year, a celebration of life and resilience of the Great Barrier Reef.

Image credit: Tourism and Events Queensland

“The Reef is beautiful, vibrant and resilient. But, after three mass coral bleaching events in five years, it is under greater pressure than ever. In many parts of the Reef, the shallow corals were hit really hard in bleaching events in 2016, 2017 and 2020. But those that survived are a genetic gold-mine of tough corals that have proved they can survive marine heatwaves.” Says GBRMPA Chief Scientist, Dr David Wachenfeld.

Marine biologist and Reef Teach Master Reef Guide Gareth Phillips explains “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. It also requires little tidal movement and mostly happens at night when plankton eaters are sleeping, giving the egg and sperm bundles a greater chance of fertilisation and survival.

“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. Most corals – 75 per cent – are hermaphrodites which means polyps are both male and female. These corals reproduce externally, producing both sperm and egg that is released in the water simultaneously during the annual coral spawning event. After the egg and sperm bundles are released, they slowly rise to the surface where they form a thick, brown slick. Now, the fertilisation process begins.
 
“The other form of reproduction is called ‘brooding’. It occurs when separate sex corals reproduce through internal fertilisation. During this process, the male coral releases sperm into the water that then swims to a female of the same species containing ripe eggs to fertilise these internally. Once fertilised, the eggs will develop into coral larva – called a planula – that can float in the water for several days or up to two months before settling on the ocean floor to start a brand-new coral colony. This is where new life begins for the corals of the Great Barrier Reef.”
 
“Year after year, this shows that despite the pressures on the Reef from climate change, there is still hope for the future,” GBRMPA Chief Scientist Dr David Wachenfeld adds.

“We encourage Australians to visit the Reef when travel is possible from their state – because when you see it and fall in love with it, you ultimately want to help protect it.

“The Reef is an amazing sight at any time of year, but the coral spawning is one of nature’s greatest spectacles and incredible to witness. You just need to be in the right place at the right time to see it.”

The above is an excerpt from an article by author Deborah Dickson-Smith.