Good news from Queensland: Certain reefs in Australia’s Great Barrier Reef Marine Park seem to have undergone a remarkable recovery since the devastating Keppel Islands coral bleaching event of 2006.

In 2006, massive and severe coral bleaching occurred around the Keppel Islands due to high sea temperatures. After being bleached, the reefs rapidly became overgrown with a species of seaweed and scientists feared this would be the end of the corals.

Picture is not from Keppel Island. It is another part of the Great barrier reef

Earlier studies have indicated that reefs that do manage to recover from catastrophes like this one need at least a decade or two to bounce back. However, a lucky combination of three previously underestimated ecological mechanisms now seems to have made it possible for the Keppel Islands reefs to make an amazing recovery, with large numbers of corals re-establishing themselves within a single year.

“Three factors were critical,” says 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). “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.“

Dr Diaz-Pulido also stresses that the astonishing recovery took place in a well-protected marine area where the water quality is at least moderately good.

Surviving tissue, not sexual reproduction

“The exceptional aspect was that corals recovered by rapidly regrowing from surviving tissue,” explains 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. This study demonstrates that for fast-growing coral species asexual reproduction is a vital component of reef resilience.”

Buying time

According to Professor Ove Hoegh-Guldberg, also of the CoECRS and The University of Queensland, understanding the different mechanisms of resilience will be critical for reef management under climate change. “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. 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.”

Dr Laurence McCook from the Great Barrier Reef Marine Park Authority agrees. “As climate change and other human impacts intensify, we need to do everything we possibly can to protect the resilience of coral reefs. 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.“

You can find out more about the remarkable recovery in the paper “Doom and boom on a resilient reef: Climate change, algal overgrowth and coral recovery”, published 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.

According to University of Queensland marine biologist Professor Ove Hoegh-Guldberg, recipient of the prestigious Eureka science prize in 1999 for his work on coral bleaching, sea temperatures are likely to rise 2 degrees C over the next three decades due to climate change and such an increase will cause Australia’s Great Barrier Reef to die.

Hoegh-Guldberg’s statement is now being criticized by other scientists for being overly pessimistic, since it does not consider the adaptive capabilities of coral reefs. According to Andrew Baird, principal research fellow at the Australian Research Council’s Centre for Excellence for Coral Reef Studies, there are serious knowledge gaps when it comes to predicting how rising sea temperatures would affect the coral.

Great barrier reef

“Ove is very dismissive of coral’s ability to adapt, to respond in an evolutionary manner to climate change,” says Dr Baird. “I believe coral has an underappreciated capacity to evolve. It’s one of the biological laws that, wherever you look, organisms have adapted to radical changes.”

According to Dr Baird, climate change would result in major alterations of the reef, but not necessarily death since the adaptive qualities of coral reefs would mitigate the effects of an increased water temperature. “There will be sweeping changes in the relative abundance of species,” he says. “There’ll be changes in what species occur where. But wholesale destruction of reefs? I think that’s overly pessimistic.”

Marine scientist Dr Russell Reichelt, chairman of the Great Barrier Reef Marine Park Authority, agrees with Dr Baird. “I think that he’s right,” says Dr Reichelt. “The reef is more adaptable and research is coming out now to show adaptation is possible for the reef.”

Professor Hoegh-Guldberg responds to the criticism by saying that the view “that reefs somehow have some magical adaptation ability” is unfounded. He also raises the question of how big of a risk we are willing to take. “The other thing is, are we willing to take the risk, given we’ve got a more than 50 per cent likelihood that these scenarios are going to come up?” professor Hoegh-Guldberg asks.”If I asked (my colleagues) to get into my car and I told them it was more than 50 per cent likely to crash, I don’t think they’d be very sensible getting in it.“