Corals go spawning, but El Nino may turn them white

Corals go spawning, but El Nino may turn them white
Whole colonies of coral releasing eggs and sperm, in an orgiastic ritual that occurs every April.

SINGAPORE - It's an orgy in Singapore waters that occurs every April.

In a ritual triggered by the light of the full moon, corals release their eggs and sperm during mass spawnings that have been described as aquatic symphonies.

The spectacle resembles an underwater snowstorm, with billions of little pink bundles bursting out from the corals in synchrony.

A few weeks ago, from April 18 to 20, a team of observers, including Minister for Manpower Tan Chuan-Jin, witnessed the love fest in dusk dives off Pulau Satumu.

In a Facebook post, the minister described his "first night dive" as "fascinating".

This year, the corals were fairly productive, spawning up to 70 per cent of the levels seen in 2010. Later that year, the reefs took a beating from a mass coral bleaching event.

For research purposes, 2010 serves as a reference year as the spawning was robust, said Karenne Tun, deputy director at the National Biodiversity Centre.

This year, at least 25 species were seen spawning, she said.

But with a 50 per cent chance of El Nino developing this year, marine biologists here are on the alert for a possible coral bleaching.

The phenomenon occurs when corals under stress lose their colour and turn white.

In May to July 2010, water temperatures in the area exceeded the bleaching threshold of 31.15 deg C. Just a tiny bump in temperature for about a month resulted in the death of nearly 5 per cent of the corals here.

Fearing another mass coral bleaching this year, the National Parks Board (NParks) has placed temperature loggers in the sea to assess the risks.

It also relies on a network of volunteers who dive in local waters to report any signs of bleaching.

Still, corals here have proved to be tough, said Dr Tun. Mortality rates following the bleachings seen in 1998 and 2010 have been lower than those suffered by other reefs in the region.

"We have a lot of optimism because our corals are quite resilient," Dr Tun told My Paper.

"If a bleaching event comes, we won't be able to control it, but we will monitor our reefs to understand how different species respond. This will help us develop management plans to safeguard the more vulnerable species."

One option could involve moving a representative sample of a sensitive species, if the bleaching is as severe as it was in 2010.

Marine biologists and conservationists here are no strangers to relocating corals, with at least five major coral transplant projects having been conducted so far.

Since late last year, the Maritime and Port Authority of Singapore (MPA) has been moving some 1,600 coral colonies from the Sultan Shoal to the southern St John's and Sisters' Islands.

The shoal will be affected by the development of a new Tuas Terminal, as MPA works to consolidate Singapore's container port activities in Tuas.

The corals relocated earlier in the year are doing well, Dr Tun said.

Over the years, techniques have been refined, and migrated corals now enjoy a better chance of survival, said reef ecology expert Chou Loke Ming.

In the 1990s, a relocation project from Pulau Ayer Chawan to a site off Sentosa saw two thirds of the corals die off but, today, the survival rate is around 70 to 80 per cent.

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