Red anthia fish and rainbow-coloured wrasse dart among the glittering reefs of Indonesia’s Wakatobi archipelago, as eagle rays and barracudas cruise past in the blue depths.
It’s hard to believe Wakatobi is anything but a thriving marine paradise, packing a bewildering abundance of life that supports 100,000 people and contributes millions of dollars to Indonesia’s economy.
But scientists are worried. Last year, coral bleaching caused by higher sea temperatures wreaked havoc across the Coral Triangle, a region of rich tropical reefs spanning much of Southeast Asia and almost all of Indonesia.
Up to 70 per cent of the coral in Wakatobi, off the southeastern tip of Sulawesi island, was totally or partially bleached. In Aceh province, off the northern tip of Sumatra, as much as 90 percent was killed, scientists said.
Experts from environmental groups The Nature Conservancy and WWF, as well as the Indonesian government, returned to Wakatobi last month to see if the marine park’s reefs had bounced back.
Over two weeks of diving at sites with names like Table Coral City and Blue Hole, the team looked for signs of long-term damage or resilience, in the hope of learning more about how reef systems respond to climate-related stresses.
“In Aceh about 90 per cent of the coral bleached, and that included some of the really big varieties that are hundreds of years old and had survived the (2004) tsunami but died because of the bleaching,” Joanne Wilson, deputy director for science in TNC’s Indonesia Marine Programme, said.
“Very fortunately in Wakatobi ... it seems that only about five to 10 percent of the corals actually died. We’re very lucky here.”
Bleaching occurs when corals respond to stress, such as stronger than normal direct sunlight or elevated sea temperatures, by expelling the algae that live inside them and give them their brilliant colours.
In normal conditions the symbiotic algae provide the corals with nutrients, and without them the corals turn white and can die within days. They may also recover, depending on the circumstances.
Dr Wilson described the “eerie” experience of diving on wintry, frozen-looking reefs during the height of the bleaching at Wakatobi last year, the warmest year on record.
Scientists feared a repeat of the 1998-1999 global bleaching that was linked to the El Nino and La Nina weather cycles in the Pacific Ocean.
About 16 per cent of the world’s reefs died in that crisis, providing a wake-up call to scientists about the dangers posed to reef systems – and the millions of people who depend on them – from global warming.
Ove Hoegh-Guldberg, the director of the Global Change Institute at the University of Queensland in Australia, said the effects of El Nino and La Nina were being magnified by “background warming” linked to general climate change.
“Over the next five to 10 years, we will probably return to fairly serious bleaching conditions,” he said.
Last year’s bleaching event has given scientists a chance to test theories of resilience and see which kinds of reefs, under which circumstances, are best suited to adapt to warmer seas.
The aim is to develop a kind of survival checklist which can be used to identify key reef systems that should be given priority in the designation of marine parks and conservation zones.
TNC’s Coral Reef Conservation director Rod Salm, who joined the Wakatobi expedition from his base in Hawaii, said last year’s bleaching hit the reefs of Thailand, Malaysia, Myanmar and Indonesia “very hard”.
“It was a tragic event but at the same time we can get something from it – we can learn how the corals respond, and we can relate how they respond back to our original resilience principles,” he said.
Other teams are doing similar studies in Aceh and Bali, looking at local characteristics and micro-climates – perhaps a cooler current or upwell of cooler water – that may indicate a better chance of surviving global warming.
The researchers will come together at a workshop next month to compare their findings.
“We’re trying to come up with the factors that are the real drivers of resilience... The idea is to identify the 10 or 12 factors that are absolutely crucial,” Dr Salm said.