Coral Rebirth on Satumu reef

Date April 23, 2018

Early this month, Hantu-blog contributor Chay Hoon was fortunate enough to witness and capture a rare event within the Singapore marine ecosystem – mass coral spawning. This mass reproductive event occurs once a year and is difficult to precisely predict. Marine biologists in Singapore have been observing local reefs for over a decade to narrow down the event to the span of a few days. Thanks to years of tenaciously pursuing their curiosity, we get to get a glimpse of this amazing event through Chay Hoon’s photos.

A coral on the Hantu reef releasing its eggs into the water.

A quick rundown of coral biology – most corals reproduce sexually, releasing sperm and eggs (which are collectively called gametes) that float to the ocean surface. At the surface, the gametes fertilize each other and form coral larvae. The larvae drift on the surface for a while more and eventually settle on the ocean floor to grow into new coral colonies! The photos from this mass spawning event were captured at Pulau Satumu, an island just south of Pulau Hantu.

Pulau Satumu is marked by the red pin!

In my opinion, the true beauty of coral spawning is that almost all the species of corals all release their eggs and sperm at the same time. This leads to a flurry of egg and sperm sacs that float through the water and slowly make their way to the surface. Along the way, the coral gametes also become food for fish and other creatures to feed on. However, the sheer number of gametes released ensures that many of the gametes make it to the surface safely.

Many tiny egg and sperm sacs are barely visible on the surface of this coral colony.

Last year, Vincent Choo managed to capture the coral spawning event on Satumu on video! The video shows just how many gametes a single coral colony can produce. With all the corals on the reef spawning at the same time, the cumulative effect is much more impressive. The water is filled with brightly coloured spheres that drift along with the current.

Aside from the impressive visual spectacle, why does it matter that the Satumu corals are spawning? Firstly, it shows that the corals are healthy. Producing such a large number of gametes is costly for the coral organisms and the creatures must invest a lot of resources into reproduction. Coral spawning thus shows that the animals have spare resources to invest and are relatively healthy.

The anemone also get in on the coral spawning action.

In addition, the synchronized timing is remarkable on its own. Imagine if the entire Singapore population could only give birth once a year, and everyone did it at the exact same time. It would probably be a pretty special day for us all. In my eyes, our coral animals are no exception and their reproductive event is worthy of celebration!

In all my dives, I have never witnessed a mass spawning event and it is something that I would very much like to see. Until that day arrives, I am resigned to view this magical event through the images and videos brought back by others from the shores off Singapore.

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