Asia-Pacific, Biodiversity, Climate Change, Environment, Headlines

ENVIRONMENT: Coral Reefs Lucky – This Time

Stephen de Tarczynski

MELBOURNE, May 6 2009 (IPS) - Scientists have been surprised by the rapid recovery of coral reefs from mass bleaching on Australia’s iconic Great Barrier Reef, but they warn that reefs remain particularly vulnerable to the effects of climate change.

“An unusual combination of circumstances led to a really lucky escape for coral reefs in the Keppel Islands,” says Dr Laurence McCook from the Great Barrier Reef Marine Park Authority – the government’s main advisory body for the Great Barrier Reef (GBR) – and the Australian Research Council’s Centre of Excellence for Coral Reef Studies (COECRS).

Large-scale coral bleaching – stress-induced loss of colour – occurred at reefs around the Keppel Islands, which lie in the southern area of the Great Barrier Reef Marine Park, in early 2006.

The world heritage-listed GBR is the largest reef system on earth, containing close to 3,000 individual reefs and 900 islands. It stretches along the coast of Australia’s north-eastern state of Queensland for more than 2,500km.

Along with other Australian-based scientists, McCook co-authored a paper on the recovery of the reefs from the adverse effects of global warming, titled ‘Doom and Boom on a Resilient Reef’, which was published Apr. 22 in the online scientific journal, PLoS ONE.

The bleaching that occurred resulted from the premature onset of high sea surface temperatures towards the end of 2005, which researchers attribute to climate change.

“The water went up a couple of degrees above the mean, so the corals rapidly responded and they bleached,” says another co-author of the ‘Doom and Boom’ report, Dr Guillermo Diaz-Pulido from the University of Queensland’s Centre for Marine Studies and COECRS.

Bleaching and mortality took place after the corals “expelled the zooxanthellae, the microscopic algae that live within the tissue,” Diaz-Pulido told IPS.

A bloom of seaweed then covered the damaged reefs, an event which could have led to total loss of the corals.

But while cases of coral bleaching resulting from climate change are not uncommon – coral reefs in the Maldives, Seychelles and Palau have suffered devastating bleaching events – the speedy recovery of reefs in the Keppel Islands amazed the scientists.

“We were astonished,” says McCook, explaining that a fortunate combination of biological circumstances was essential to the corals’ resurgence.

“Most of the seaweeds died back because of their own inherent seasonality, and that gave the corals the chance to recover. The second factor was that the corals had this spectacular growth ability.”

Normally, when bleaching occurs to the extent that it did in the Keppel Islands – in this case, bleaching affected an estimated 77 to 95 percent of coral colonies – reefs take more than a decade to recover.

“Baby corals basically have to come in from a distant reef, settle and grow to re-establish coral populations,” McCook told IPS.

But surviving tissue in the bleached corals was able to take advantage of the seaweed’s die-back, leading to the dramatic recovery of coral populations just a year after they were decimated.

While scientists say that luck played a vital role in the coral re-growth on the reefs, they point out that good management of the marine environment was also important.

“The Great Barrier Reef Marine Park is being well managed in terms of water quality,” says Diaz-Pulido.

Although shipping and aquaculture, as well as run-off from coastal development and agriculture remain threats to the water quality at the GBR, the park’s authorities aim to protect the reef system through zoning and regulatory practices.

Among other concerns for park officials are over-fishing and tourism. Each year, close to two million tourists and five million recreational visitors spend time at the GBR.

But McCook says authorities are “doing everything we can to manage those risks, and there’s no doubt that was a factor in the recovery that we saw.”

He says that compared to many reefs around the world, “especially in the Caribbean where there has been widespread degradation,” reefs in Australian waters reap the benefits of the nation’s relative prosperity.

But the marine scientist warns that the threat to reefs posed by climate change means that “we need to continue to be as watchful and as careful as we can be.”

Global warming represents a major danger to the existence of coral reefs, particularly through ocean warming and ocean acidification. Besides bleaching, stronger and more frequent storms are expected to lead to increased coral mortality, while slower growth rates of coral are also anticipated as sea levels rise.

According to networks of coral reef conservation groups, much damage has already been done to the “rainforests of the ocean”, so called due to their biodiversity.

The International Coral Reef Action Network says that the decade to 2008 – last year was the ‘International Year of the Reef’ – saw unprecedented levels of deterioration in coral reefs, while Brian Huse, executive director of the United States-based Coral Reef Alliance says that reefs continue to decline “at an alarming rate.”

Huse argues that although the world’s coral reefs support the livelihoods of some 100 million people through income and food – in addition to the protective barrier they provide for coastal communities – “we could lose up to 70 percent of the world’s coral reefs by 2050.”

McCook agrees that the outlook for reefs remains grim.

“It is pretty gloomy. There’s pretty broad scientific consensus that the combined effects of climate change are going to have a lot of direct impacts,” he says.

McCook warns that while a combination of lucky circumstances and good management saved the coral reefs around the GBR’s Keppel Islands this time, efforts to tackle climate change at its source, rather than attempts to mitigate its effects, are required for the long-term survival of such fragile ecosystems.

According to scientists, protection measures such as those implemented by the GBR’s marine park authority are about “buying time” for coral reefs.

“In many ways, what we do is we buy time as we, hopefully, set about addressing the cause of climate change,” McCook says.