Experts fear mass coral bleaching when El Nino returns

Tan Qiuyi Channel NewsAsia 8 Jun 14;

SINGAPORE: The world is bracing for El Nino this year, which could mean months of drought and sweltering temperatures for Southeast Asia.

You may be feeling the heat on the ground, but one of the most dramatic and potentially catastrophic consequences of El Nino is underwater -- on the world's coral reefs.

Singapore has lost up to 60 per cent of its coral reefs due to development since the 1960s, but what remains today still supports rich marine life.

And they are no less vulnerable to the threat of warming seas.

Most of Singapore's reefs are located on the fringes of its southern islands.

Coral cover today is only about 40 per cent of what the country had in the 1950s -- most of it lost to coastal development, land reclamation and seabed dredging over the past 50 years.

What remains is threatened by more reclamation to meet land use demands by 2030.

But for now, marine biologists have a more pressing, global threat to deal with.

Underwater, researchers from the National University of Singapore's (NUS) Reef Ecology Lab survey the natural reef off Semakau.

Lionel Ng, a research assistant with Reef Ecology Lab, said: "Most of the corals were quite OK. Less than five per cent, I would say, were bleaching."

That's good news for now, but marine biologists fear a return of the mass coral bleaching that took place in 1998 and 2010 when the region was swept by unusually warm seawater -- a result of El Nino.

Experts say this disruptive weather phenomenon is likely to hit again in 2014.

Assistant Professor Winston Chow from the NUS Geography Department said: "We're seeing warmer than usual conditions throughout the entire tropical or equatorial Pacific Ocean. It's greater than 0.5 degrees Celsius compared to the long-term average, which is a precursor of El Nino conditions. The warmth of the Pacific Ocean extends all the way towards the South China Sea and also into our part of the world in Southeast Asia."

In healthy conditions, algae living on coral tissue absorbs the sun's energy and produce food for the algae as well as their coral hosts.

When the water gets too warm, the algae produces harmful toxins.

As a result, coral polyps expel the coloured algae and turn white, the actual colour of coral tissue.

Coral can survive bleaching, but lack of food from the algae causes stress and makes it more prone to disease.

So prolonged bleaching can kill entire reefs.

Whether El Nino will happen more often from now on remains a question for climatologists, but there are signs extreme weather is the "new normal".

Assistant Professor Chow said: "The baseline conditions have changed. What we considered in the past to be extreme events could likely become normal events, going forward in the future.

"So more droughts and higher temperatures would be a concern, going forward."

Since May this year, corals in Singapore waters, especially those closer to the water surface, have started to show signs of stress.

There is not much one can do to stop corals from bleaching if and when it happens, because it's all about the temperatures of the oceans around us.

But what the researchers in Singapore are doing can help them find ways to improve the long-term survival chances of Singapore corals.

Since 1997, university researchers have been collecting coral fragments and growing them on man-made coral nurseries off Pulau Semakau.

The nursery anchors the fragments in a sheltered environment, allowing them to grow larger and stronger, before they are transplanted.

Toh Tai Chong, a PhD student at Reef Ecology Lab, said: "First, we do want to study the responses of these corals to bleaching, and thermal stress, as well as move some of these coral fragments to nursery sites with higher water flow.

"So this helps reduce the effect of thermal stress. In the event the corals on the reefs are being wiped out, we can use these as transplant material to re-colonise the reef."

Around the world, coral reefs are declining.

However, despite facing the double whammy of coastal development and climate change, Singapore's reefs continue to survive.

This gives hope to scientists.

Dr Karenne Tun, NParks deputy director (National Biodiversity Centre), said: "The two major bleaching events in 1998 and 2010, we did see a dip in coral cover, amount of corals on the reef. So after the event, the coral cover went down.

"But then, they recovered several years later. This kind of long-term monitoring data gives us the ability to pick out these signals, so we know that there is a chance that if there's another bleaching event now, our corals have a good chance of recovering because they've shown that in the past two decades.

"It's not something that's obvious to people, but it basically means we have reefs that you can probably keep on diving at for a long time to come."

The resilience of Singapore's coral reefs lies in their diversity, which lowers the risk of entire reefs being wiped out.

There are about 250 coral species in Singapore, out of 600 for the whole of Southeast Asia.

And there could be more -- as marine biologists have only scratched the surface of what's underwater.

Dr Karenne Tun said: "There are so many new species that haven't been discovered or recorded in Singapore. We don't really have a good grasp of what we have, and if we lose it faster than we get that information, then we lose a whole body of knowledge that's there."

Studying how and why Singapore's reefs survive and adapt to warmer seas could well offer answers to coral conservation efforts in Singapore and elsewhere.

We don't know.

But if we lose the reefs, we will never find out.


- CNA/ir