30 Nov 2018

Have you heard of the biggest breeding event on the Great Barrier Reef? It’s part Russian Roulette and part perfectly synchronised diving.  Once a year, for a week, all the coral polyps on the Great Barrier Reef release their eggs and sperm into the water with the hope that they collide, find somewhere to settle in and grow into new corals.

Coral spawning happens sometime in November, an exact date can’t be predicted with accuracy as there are three important factors that must line up before spawning happens. The polyps wait until after the full moon and for the water temperatures to increase with the start of summer months. When these elements line up the coral polyps wait for nightfall and then release the eggs and sperm into the water, the result resembles an underwater snowstorm of red, yellow, orange and white.

After the spawning event there are hundreds of thousands of fertilised coral eggs floating through the water looking for somewhere to settle. This is the part that feels most like Russian Roulette. Despite this event being discovered in the 1980s by Southern Cross University professors, there is little data around how many of these fertilised eggs make it to safe ground to grow.

Nature is a formidable and surprisingly calculated being and this great event is one of the best examples. With all types of coral (there are over 400 on the Great Barrier Reef alone) spawning at once, how do we not have hundreds of hybrids in existence? Nature is two steps ahead here; to prevent hybrid corals the spawning happens in stages, with the same corals spawning at once to create new corals of that species only.  Pair this intelligence with all the timing factors of this event and you can see why reef enthusiasts and scientists are drawn to this event year after year in awe of what can be achieved by coral polyps.