Experts sound alarm as corals show new spate of bleaching

By Christiane Oelrich Oct 8, 2010, 12:56 GMT

   Singapore - Marine experts are sounding the alarm after underwater surveys revealed widespread bleaching of the world's coral reefs.

   Twelve years after the severe global bleaching of 1998, corals are once again showing signs of stress from rising water temperatures. Experts fear that 2010 may be another very bad year for the world's reefs.

   Up to 90 per cent of Thailand's corals are bleaching, experts said, while significant paling is affecting reefs off Indonesia's island of Sumatra and in the Caribbean.

   Scientists blame the rise in water temperature for the bleaching. It does not kill the coral directly, but does leave it vulnerable to disease and unable to reproduce, which often leads to its death.

   Corals have a symbiotic relationship with algae, said Clive Wilkinson of the Reef and Rainforest Research Centre in Townsville, on Australia's north-eastern coast, not far from the Great Barrier Reef, the world's largest coral reef.

   'They take the algae virtually prisoner, so the algae have to produce sugar for the corals,' he explained.

   'With high temperatures and bright sunshine, the algae start creating toxins. The corals then spit out their energy source. The coral is still alive, but starving and susceptible to disease. They have no energy for reproduction and eventually die.'

   The algae are what lend the coral its eye-catching colours. The loss of the algae causes it to take on a bleached appearance.

   Wilkinson, who heads the Global Coral Reef Monitoring Network, is alarmed by its findings this year, which he said could be as bad as 1998, when 16 per cent of the world's coral was lost.

   This year has so far seen a global water temperature on average 0.67 degrees Celsius higher than in the middle of the last century, exactly the same average temperature as in 1998.

   'In South-East Asia, this has led to bleaching that was extremely severe,' said Mark Easkin, director of the coral programme at the US National Oceanic and Atmospheric Administration (NOAA).

   Eakin and Wilkinson said they fear worse to come, unless the weather takes a turn for the worse.

   'Only a string of hurricanes can can influence this very quickly,' he said. Hurricanes cause a drop in temperature in the shallow waters where corals live.

   Australia is 'having a big wet season and expects cyclones' during the southern hemisphere's summer, Wilkinson said, adding that he hoped the bad weather would mitigate the impact of the rising temperatures on the Great Barrier Reef.

   The nooks and crannies of coral reefs provide habitats for crabs, starfish and other small marine creatures.

   Many fish species use the coral as protective nurseries for their young, as well as feeding off them. 'The reefs are the start of complex food chains,' Wilkinson said.

   Those food chains reach far beyond the ocean. 'The fish that grow and live on coral reefs are a significant food source for over a billion people worldwide,' the NOAA said.

   There have been seven widespread bleachings since 1979, the NOAA reported, all linked to temperature changes, although other factors can cause the phenomenon.

   Wilkinson is convinced climate change is at least partly to blame. 'In 1998, people said 'this is a millenium event,' in 2005 in the Caribbean they said the same thing, and now again? Hardly possible,' he said.

   There are no quick fixes to the problem. Australian experiments to build shades for the reefs have had limited success.

   'A dive operator could do that, shade a reef that he takes his clients to,' Wilkinson said. 'But on a large scale - how many billions have you got?'

   In Thailand, several dive centres have given up taking divers to the fading reefs in favour of visiting wrecks.

   Without a reduction in the greenhouse gases widely held responsible for the warming of the atmosphere and the seas, the long-term prospects are bleak, Wilkinson said.

   Coral has started to grow again on half of the reefs that suffered bleaching in 1998, he said, but this did not mean it had recovered.

   'In the Maldives, virtually all corals had died in 1998,' he said. 'Surveys said the corals were extinct, but then juveniles started reappearing. Down in the deep banks there were living corals that had spawned.'

   'But this is like a forest fire - whoever gets in first after that has the best chance of growing. The slower ones have a hard time. To the average tourist it looks good, but for a scientist it is very different.'