Great Barrier Reef suffered worst bleaching on record in 2016, report finds

By Hywel Griffith
BBC News, Sydney

media captionWarmer water has led to the worst destruction of coral ever recorded on the Great Barrier Reef

Higher water temperatures in 2016 caused the worst destruction of corals ever recorded on Australia's Great Barrier Reef, a study has found.

Some 67% of corals died in the reef's worst-hit northern section, the ARC Centre of Excellence for Coral Reef Studies report said.

The situation was better in the central section, where 6% perished, while the southern reef is in good health.

But scientists warn recovery could be difficult if climate change continues.

Coral bleaching happens when water temperatures rise for a sustained period of time.

image copyrightARC Centre of Excellence for Coral Reef Studies
image captionWarmer waters has led to the worst destruction of coral ever recorded on the Great Barrier Reef

In February, March and April, sea surface temperatures across the Great Barrier Reef were the hottest on record, at least 1C higher than the monthly average.

"Some of the initial mortality was down to heat stress," said study leader Professor Terry Hughes.

"The coral was cooked."

How bleaching occurs

Far more has been lost through gradual starvation, after the coral expelled the colourful algae zooxanthella, which turns sunlight into food.

This is what leads to the white, skeletal appearance of the coral, which is left without its main source of energy.

image copyrightARC Centre of Excellence for Coral Reef Studies
image captionFor three months, sea temperatures were a degree higher than average

The study also found that the coral which survived the bleaching have now come under greater threat from predators such as snails and crown of thorns starfish.

This year's mass bleaching was the worst-ever recorded on the Great Barrier Reef, following two previous events in 1998 and 2002.

Professor Hughes is certain that the increased water temperature is the result of carbon emissions, and warns that climate change could bring annual bleaching within 20 years.

"Most of the losses in 2016 have occurred in the northern, most pristine part of the Great Barrier Reef," he said.

"This region escaped with minor damage in two earlier bleaching events in 1998 and 2002, but this time around it has been badly affected."

Where is the damage?

One of the worst-hit areas is around Lizard Island in Far North Queensland, where around 90% of the coral has died.

Dr Andrew Hoey, whose team charted the area, said the impact was far worse than feared after an initial survey in April.

"It's devastating to get in the water somewhere you've been coming for almost 20 years, and it's just knocked it on its head," he said.

image copyrightARC Centre of Excellence for Coral Reef Studies
image captionBleaching is caused when water temperatures rise for a sustained period

"There's very little coral cover left there. It was dominated by the acropora - the branching corals - but we lost most of them."

Lizard Island is home to a research station, where scientists from across the world have come for decades to study marine life

One of its directors, Dr Anne Hogget, said this was by far the worst event to hit the Great Barrier Reef since she started working there in 1990.

"We had bleaching here in 2002," she said. "We thought this was bad at the time, but this has blown it completely out of the water."

She is hopeful that the reef is capable of recovery, but fears it may not be give an opportunity, as sea temperatures continue to rise.

image captionDr Andrew Hoey (pictured) said the loss was far worse than feared

"The trajectory is not good," Dr Hogget explained.

"We keep pumping carbon dioxide into the atmosphere, and this happened absolutely because of that."

What happens next?

On the central and southern parts of the Great Barrier Reef, where bleaching was not as prevalent, there is concern that it has been misreported, with one magazine even publishing an obituary of the reef earlier this year.

Tourism operators like Michael Healey from the Quicksilver Group are keen to point out that many sites were unaffected, but there is concern for the reef's long term health.

"Without the Great Barrier Reef, we wouldn't survive," he said.

"So it is absolutely of the utmost importance that we ensure that our politicians and everyone else in our community and around the world are doing what they can."

image copyrightARC Centre of Excellence for Coral Reef Studies

The Australian Government has published a long-term sustainability plan for the reef, and pledged financial support for research into coral bleaching.

The 2050 plan identifies the need to help make the reef more resilient to climate change in the future, while trying to lower carbon emissions.

Mr Healy argued even those not financially involved had a stake in the reef.

"I'd say every human on the planet does," he said.

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