Reef boom beats doom
The University of Queensland Australia 21 Apr 09;
Marine scientists say they are astonished at the spectacular recovery of certain coral reefs in Australia's Great Barrier Reef Marine Park from a devastating coral bleaching event in 2006.
That year high sea temperatures caused massive and severe coral bleaching in the Keppel Islands, in the southern part of the Great Barrier Reef. The damaged reefs were quickly smothered by a single species of seaweed � an event that can spell the total loss of the corals.
However, a lucky combination of rare circumstances meant the reefs were able to achieve a spectacular recovery, with abundant corals re-established in a single year, said Dr Guillermo Diaz-Pulido, from the Centre for Marine Studies at The University of Queensland and the ARC Centre of Excellence for Coral Reef Studies (CoECRS).
Dr Diaz-Pulido said that the rapid recovery was due to an exceptional combination of previously-underestimated ecological mechanisms.
"Three factors were critical," he said.
"The first was exceptionally high regrowth of fragments of surviving coral tissue. The second was an unusual seasonal dieback in the seaweeds, and the third was the presence of a highly competitive coral species, which was able to outgrow the seaweed.
"But this also all happened in the context of a well-protected marine area and moderately good water quality.
"It is rare to see reports of reefs that bounce back from mass coral bleaching or other human impacts in less than a decade or two.
"The exceptional aspect was that corals recovered by rapidly regrowing from surviving tissue," said Dr Sophie Dove, also from CoECRS and The University of Queensland.
"Recovery of corals is usually thought to depend on sexual reproduction and the settlement and growth of new corals arriving from other reefs," she said.
"This study demonstrates that for fast-growing coral species asexual reproduction is a vital component of reef resilience."
Professor Ove Hoegh-Guldberg of the CoECRS and The University of Queensland said that coral reefs globally were increasingly being damaged by mass bleaching and climate change.
Their capacity to recovery from that damage was critical to their future, he said.
"Our study suggests that managing local stresses that affect reefs, such as overfishing and declining water quality, can have a big influence on the trajectory of reefs under rapid global change," Professor Hoegh-Guldberg said.
"Clearly, we need to urgently deal with the problem of rising carbon dioxide in the atmosphere, but managing reefs to reduce the impact of local factors can buy important time while we do this."
Understanding the different mechanisms of resilience is critical for reef management under climate change.
"Diversity in processes may well be critical to the overall resilience and persistence of coral reef ecosystems globally," said Dr Laurence McCook, from the Great Barrier Reef Marine Park Authority.
The research was partially funded by a Pew Fellowship in Marine Conservation awarded to Dr McCook, the Great Barrier Reef Marine Park Authority as well as the ARC Centre of Excellence program.
"This combination of circumstances provided a lucky escape for the coral reefs in Keppel Islands, but is also a clear warning for the Great Barrier Reef," Dr McCook said.
"As climate change and other human impacts intensify, we need to do everything we possibly can to protect the resilience of coral reefs."
The research was published this week in the paper Doom and boom on a resilient reef: Climate change, algal overgrowth and coral recovery, in the journal PLoS ONE, by Guillermo Diaz-Pulido, Laurence J. McCook, Sophie Dove, Ray Berkelmans, George Roff, David I. Kline, Scarla Weeks, Richard D. Evans, David H. Williamson and Ove Hoegh-Guldberg.
'Lucky escape' for Australian coral reef
AFP Yahoo News 23 Apr 09;
SYDNEY (AFP) – A section of Australia's Great Barrier Reef, which scientists have warned could be killed by global warming within decades, has regenerated itself in record time, a scientist said Thursday.
But Laurence McCook, head of research for the authority that preserves the World Heritage-listed reef, said the giant organism remained at serious threat of climate change and labelled the partial regeneration a "lucky escape.".
The badly damaged stretch of coral at Keppel Island, at the reef's southern end, became strangled by seaweed after it began bleaching in 2006 due to elevated sea temperatures and acidity, the results of global warming.
Bleaching occurs when the plant-like organisms that make up coral die and leave behind the white limestone skeleton of the reef.
Bleached coral usually takes up to 10 years to regrow by a process of "reseeding," when larvae from a distant reef is carried by currents to repopulate the damaged area.
But in an unusual combination of circumstances, McCook said, the Keppel reef managed "asexual regrowth" from surviving tissue fragments and had returned to abundance in just 12 months.
"This is very unusual because it was a single species of seaweed and it's a species that dies back in winter," McCook told AFP.
"Then some of the coral had actually maintained enough surviving tissue that they were actually able to grow much faster than we would normally expect."
But he urged caution about the finding, describing it as an unusual and rare combination of the perfect conditions.
"If the reefs had been heavily polluted, if the area had been overfished, if tourism wasn't being well managed, all of those things could lead to the reef failing to recover," he said.
While the overall health of the Great Barrier Reef was "relatively good on a global scale," McCook said it was under very serious threat from climate change and other human impacts.
"This is a timely warning of just how serious the damage (can be) that climate change can cause. We had a lucky escape because of these unusual circumstances and that is a rare event," he said.
The reef, which is treasured as the world's largest living organism, stretches for 345,000 square kilometres (133,000 square miles) off Australia's northeast coast.
Coral growth has slowed markedly on the reef since 1990, believed to be caused by warmer seas and higher acidity.
