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Spawning corals put up awesome spectacle

03 May 2012

(From left) Marine biologists Toh Kok Ben and Tay Ywee Chieh preparing for their dive. The researchers from the NUS Reef Ecology Laboratory are members of the coral spawning monitoring team

A Favites hard coral releasing egg-sperm bundles, which break apart on reaching the water surface

Photos: Karenne Tun
"Astra inclinant, non necessitant", Latin for "The stars incline, they do not determine", is perhaps a good description of the yearly synchronous mass spawning that occurs on coral reefs all over the world.

The awesome show put up by nature happened in the waters of Singapore during the full moon period in April this year. The spectacular phenomenon was captured by a team of coral reef biologists - comprising members from NUS, National Parks Board and the National Institute of Education - who have been monitoring and documenting the event near Raffles Lighthouse over the last decade.

When the observation was first initiated in 2002 by Dr James Guest, then a PhD student at NUS investigating the reproductive patterns of Singapore corals, there was no prior information of such activities in the local reefs. Over the years and through numerous week-long expeditions studying and documenting the spawning at night, a few clear patterns had emerged.

Although strongly influenced by seasonal and lunar patterns, the colourful spectacle by nature is unique in various geographies and time zones. These differences can be attributed to the start of the spawning window, the total number of spawning days and the composition of species participating in the event.

In Singapore, synchronous mass spawning usually occurs after the Easter full moon in late March or April. It takes place from the second to seventh day after the full moon, peaking between the third and fifth days. The number of species participation varies, with some displaying population-wide participation. The spawning times also varied over the years, ranging from dusk at 7.20pm to around 9.30pm at night.

One of the most interesting discoveries by the team is the distinguishable spawning characteristics unique to each coral species. These features have enabled the biologists to home in on spawning corals by just observing the shape, colour and size of the egg bundles floating in the water. The scientists can thus record more species participation over the years, especially those with very narrow spawning windows lasting only a few minutes.

The team has been finding new species participation even after 10 years of survey. This year, they spotted four new species participation, bringing the total number recorded to 73 species, or close to 30 per cent of Singapore's coral species.

By Karenne Tun, PhD candidate, Department of Biological Sciences