Ocean Heat Wave Wreaked Havoc on Great Barrier Reef

Gbr bleaching21

Between March and November 2016 the Reef experienced an extended heatwave, and the ARC Centre of Excellence for Coral Reef Studies (Coral CoE), working out of Cairn's James Cook University, studied the disastrous effects this had on the Reef and its ecosystems.

Tim McClanahan, a conservation zoologist at the Wildlife Conservation Society in Mombasa, Kenya, says the study's findings might not predict how other reefs will cope with a warmer world.

In surveying the 3863 individual reefs that make up the system off Australia's north-east coast, scientists found that 29 percent of communities were affected.

The coral bleaching event of March 2016, triggered by prolonged high ocean temperatures, dealt such a shock to the reef that millions of corals died nearly immediately, researchers found.

"The 2016 bleaching event triggered an unprecedented loss of corals on the northern third of the Great Barrier Reef, and to a lesser extent, the central third, with nearly no heat-stress mortality occurring further south", the report, published today in Nature, found.

The Great Barrier Reef suffered a catastrophic die-off after two back-to-back marine heat waves in 2016 and 2017, a new study finds - and many of its reef communities have been fundamentally changed. These were combined with underwater surveys at over 100 locations. "That's why it's so important that we deal with carbon dioxide levels in the atmosphere", he said. This rapid onset is not the same starvation mechanism. "They cooked because the temperatures were so extreme".

Researchers across Australia and the world are attempting to save the Great Barrier Reef and other coral reefs like it by developing heat-resistant coral, creating 3D simulations to track erosion and showing the world (in VR no less) what we stand to lose. It was dead and overgrown by algae by April 2016.

The team found that the northern third of the reef was hit hardest, with many corals dying immediately from "heat stress", while corals with more complex branching structures were also more susceptible to bleaching.

Not all areas of the reef, or all coral species, were equally affected.

"There have been some signs of recovery", said Dr Heron.

In years to come, sprawling and intricately shaped coral species such as the Staghorn variety will be largely replaced by flat, mound-shaped formations.

The paper repeated previous science suggesting parts of the reef may never recover from the 2016 bleaching, and again called for more urgent action to prevent its decline as a result of climate change. (In 2017, another ocean heat wave claimed another roughly 20 per cent of corals, Hughes said.) Many corals died faster than expected and at a lower level of sustained heat than had been predicted to be deadly. Deprived of their colorful partners, corals turn bone-white and will starve and die unless water temperatures cool and the zooxanthellae return.

As it stands, the makeup and mix of species of the Great Barrier Reef have already started to change. Record high temperatures in 2016 were followed by another bleaching event a year ago.

"We're very concerned that the return period between events is now much shorter than the recovery time required", he told BBC News. "Before the study we didn't know where those tipping points were".

"Will there be a reef? Yes".

Such events, though, tend to carve a swathe through the reef, perhaps 50 to 100 kilometres wide, with patchier damage than mass bleaching.

Prof Jörg Wiedenmann from the University of Southampton's Coral Reef Laboratory agrees that, if present conditions continue, significant change lies ahead.

"If we fail to curb climate change, and global temperatures rise far above 2 degrees (Celsius), we will lose the benefits they provide to hundreds of millions of people", Terry Hughes, the lead author of the report and director of the coral-reef centre at James Cook University, said.

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