More than one-third of the coral reefs of the central and northern regions of the Great Barrier Reef have died in the huge bleaching event earlier this year, Queensland researchers said.
Corals to the north of Cairns – covering about two-thirds of the Great Barrier Reef – were found to have an average mortality rate of 35 per cent, rising to more than half in areas around Cooktown.
The study, of 84 reefs along the reef, found corals south of Cairns had escaped the worst of the bleaching and were now largely recovering any colour that had been lost.
Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, said he was "gobsmacked" by the scale of the coral bleaching which far exceeded the two previous events in 1998 and 2002.
"It is fair to say we were all caught by surprise," Professor Hughes said. "It's a huge wake up call because we all thought that coral bleaching was something that happened in the Pacific or the Caribbean which are closer to the epicentre of El Nino events."
The El Nino of 2015-16 was among the three strongest on record but the starting point was about 0.5 degrees warmer than the previous monster of 1997-98 as rising greenhouse gas emissions lifted background temperatures. Reefs in many regions, such as Fiji and the Maldives, have also been hit hard.
Bleaching occurs when abnormal conditions, such as warm seas, cause corals to expel tiny photosynthetic algae, called zooxanthellae. Corals turn white without these algae and may die if the zooxanthellae do not recolonise them.
The northern end of the Great Barrier Reef was home to many 50- to 100-year-old corals that had died and may struggle to rebuild before future El Ninos push tolerance beyond thresholds.
"How likely is it that they will fully recover before we get a fourth or a fifth bleaching event?" Professor Hughes said.
The health of the reef has been a contentious political issue, with Environment Minister Greg Hunt pledging more funds in the May budget to improve water quality – one aspect affecting coral health.
But Mr Hunt has also had to explain why his department instructed the UN to cut out a section on Australia from a report that dealt with the threat of climate change to World Heritage sites including the Great Barrier Reef and Kakadu.
'10 cyclones holding hands'
Professor Hughes said tropical cyclones can cut a 50km-wide swatch of destruction of corals, but this year's bleaching event was like "10 cyclones holding hands and marching across the northern third of the Great Barrier Reef".
But cyclones can also help. The category-five Cyclone Winston that slammed into Fiji in February, brought widespread rains over parts of Queensland as a tropical depression, helping to lower sea temperatures by two degrees and sparing much of the southern corals from severe bleaching, Professor Hughes said.
Even so, those southern reefs are still likely to have had their reproduction and growth rates slowed by the unusually warm seas. The scientists said the bleaching event showed how important it was to continue to bolster resilience of the reef, such as through programs to limit run-off from farms and towns bringing in excessive nutrients and pollution.
"The reef is no longer as resilient as it once was, and it's struggling to cope with three bleaching events in just 18 years," Professor John Pandolfi, from the ARC Centre of Excellence for Coral Reef Studies at The University of Queensland, said. "Many coastal reefs in particular are now severely degraded."
(Use the slider on image below to see mature staghorn coral at Lizard Island on the Great Barrier Reef. The corals bleached in February 2016 and were overgrown with algae by April.)
Professor Hughes said he did not advocate the reef being put on the "in danger" list by the World Heritage Committee, but it was time governments reconsidered their approval for massive new coal mines in Queensland's Galilee Basin and elsewhere.
"The key threat to the Great Barrier Reef is climate change – the government has recognised that many times," he said.
"[But] there is a disconnect in the policy round governments issuing permits for 60 years for new coal mines and how that might impact on the Great Barrier Reef and reefs more generally."
Most coral dead in central section of Great Barrier Reef, surveys reveal
As mass bleaching sweeps the world heritage site, scientists also find an average of 35% of coral dead or dying in the northern and central sections of the reef
Michael Slezak The Guardian 29 May 16;
The majority of coral is now dead on many reefs in the central section of the Great Barrier Reef, according to an underwater survey of 84 reefs, in the worst mass bleaching event to hit the world heritage site.
An average of 35% of coral was now dead or dying in the northern and central sections, according to the surveys led by the Australian Research Council’s Centre of Excellence for Coral Reef Studies.
But in good news for tourists and the tourism industry, only 5% of coral has died on reefs south of Cairns.
The in-water mortality studies followed earlier aerial surveys, which found that 93% of the Great Barrier Reef had been affected by bleaching.
Coral bleaches when it gets too hot for too long. The water temperature stresses the coral and it expels the colourful algae it relies on to give it energy. If warm conditions persist, the coral dies and can get taken over by seaweed.
But if the water returns quickly to temperatures that are no longer stressful, the coral can recover, regaining its symbiotic algae. That is what researchers expect to happen to most of the bleached coral south of Cairns.
“Fortunately, on reefs south of Cairns, our underwater surveys are also revealing that more than 95% of the corals have survived, and we expect these more mildly bleached corals to regain their normal colour over the next few months,” said Mia Hoogenboom from James Cook University.
The conditions that led to the bleaching event were estimated to have been virtually impossible if it were not for the greenhouse gases humans have released into the atmosphere. Models showed they would be average conditions within 20 years.
Terry Hughes from James Cook University, who led the survey work, said: “This year is the third time in 18 years that the Great Barrier Reef has experienced mass bleaching due to global warming, and the current event is much more extreme than we’ve measured before.
“These three events have all occurred while global temperatures have risen by just 1C above the pre-industrial period. We’re rapidly running out of time to reduce greenhouse gas emissions.”
Great Barrier Reef bleaching made 175 times likelier by human-caused climate change, say scientists
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John Pandolfi from the University of Queensland said the reef was already struggling to cope with the regularity of the bleaching events.
He said the reef was no longer as resilient as it once was. “It is critically important now to bolster the resilience of the reef, and to maximise its natural capacity to recover,” said Pandolfi.
The reef’s ability to recover from the increasingly regular bleaching events is being hampered by water pollution.
A recent study suggested $10bn investment was needed to adequately reduce pollution levels and improve the reef’s resilience.
The bleaching hitting the Great Barrier Reef is part of a global bleaching event, partly driven by a massive El Niño and climate change. By February this year, the event was already the longest-running global bleaching event in history, and it is expected to continue into the coming months.
Bleaching May Have Killed Half the Coral on the Northern Great Barrier Reef, Scientists Say
MICHELLE INNIS New York Times 29 May 16;
SYDNEY, Australia — Mass bleaching on the Great Barrier Reef in the past three months has killed as much as half of the coral in the north but left large parts of the southern reaches with only minor damage, scientists in Australia said on Sunday.
The current bleaching is the third to strike the roughly 1,400-mile-long reef in 18 years and the most extreme scientists have recorded.
“In the north, the mortality rates are off the scale,” said Prof. Terry Hughes, the director of the ARC Center of Excellence for Coral Reef Studies, based at James Cook University in Townsville, Queensland. “There, the coral mortality rates are approaching 50 percent, and the impact of the bleaching is still unfolding.”
But from Cairns, in tropical north Queensland, southward down the east coast of the state, about 95 percent of the coral has survived, Professor Hughes said. Mildly bleached coral should regain its color over the next few months, although the stress from bleaching is likely to slow the area’s reproduction and growth, he said.
Bleaching occurs when water temperatures rise as little as 1 degree Celsius, or 1.8 degrees Fahrenheit. The coral then expels tiny, colorful algae, causing it to turn white. The coral can recover if the water temperature drops and the algae, known as zooxanthellae, recolonize it. Otherwise, it may die.
Scientists diving on the reef in March and April recorded an average death rate of 35 percent for bleached coral in the north and central parts of the reef. Mass bleaching reduces the disparity between corals that might survive and those that are more vulnerable, resulting in higher death rates across the reef, Professor Hughes said.
Another scientist, Verena Schoepf from the University of Western Australia, said portions of the reef off the Kimberley coast had suffered severe but patchy bleaching and death rates of about 15 percent so far in the current bleaching event. The Kimberley region is across the far north of the state of Western Australia.
“We are seeing these events occur so close together, due to global warming, that coral does not have time to recover,” Professor Hughes said. “Some of the large, 50- to 100-year-old corals we saw on the very northern parts of the reef are now dead. We won’t see them there again.”