Coral bleaching on the Great Barrier Reef during a mass bleaching event in 2017 (Getty)
‘Coral bleaching’ due to climate change poses a – but could it be reversed?
A new study by Californian researchers offers hope that the damage of ‘bleaching’ might be reversible and that .
Corals receive some of their nutrients through a symbiotic relationship with photosynthetic algae which live inside their cells.
High ocean temperatures cause a breakdown in the symbiosis resulting in a ‘bleached’ coral that has expelled the algae.
If symbiosis is not initiated within a few weeks, the coral will starve to death.
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The new study shines new light on the symbiosis – finding that although photosynthesis by algae is a key part of the symbiotic relationship it is not required to initiate symbiosis.
The finding could lead to strategies that might prevent warmer oceans from breaking the symbiotic relationship between the two organisms and saving what remains of the world’s corals.
Robert Jinkerson, an assistant professor of chemical and environmental engineering at UCR, and Tingting Xiang, an assistant professor of biological sciences at the University of North Carolina at Charlotte, led a team to create mutant Symbiodiniaceae algae – and use these mutants to investigate symbiosis with cnidarians
Co-lead author Joseph Russo said, “Time is of the essence regarding the protection of the coral reefs, and our hope is that these mutants will allow ourselves and others to increase the overall pace towards this goal.”
“Our study highlights the power of forward genetic approaches to probe cnidarian Symbiodiniaceae symbiosis and provides a promising platform to answer key questions in symbiosis and ultimately develop strategies to save corals,” said Xiang.
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A study found that coral reefs are expected to see huge changes in the water around them by the second half of this century.
The researchers found that 60% to 87% of the ocean is expected to experience multiple biological and chemical changes, such as increases in water temperature, higher levels of acidity and changes in oxygen levels, by the year 2060.
The rate of change is expected to be even higher, 76% to 97%, in very large marine protected areas such as Australia’s Great Barrier Reef Marine Park and the Galapagos Marine Reserve in Ecuador.
“What we’re looking at here is the potential extinction of a whole environment,” said Watson, who specialises in marine social-ecological systems and understanding complex adaptive systems.
“In some places, the environments we have today are not going to exist in the future. We won’t be able to go visit them or experience them. It is an environmental, cultural and economic loss we can’t replace.”
Watch: Florida scientists use human medicine to help save coral reefs
Dead corals are being recorded in aerial surveys across the Great Barrier Reef in what the marine park’s chief scientist says is a widespread and serious bleaching event on the world heritage icon.
Aerial surveys have covered half of the 2,300km reef, with the worst bleaching observed in the park’s central region off Townsville, where corals on some reefs are dead and dying.
The unfolding bleaching comes ahead of a 10-day UN monitoring mission to the reef due to start on Monday.
Leading reef scientist Prof Terry Hughes said this week a sixth mass bleaching event was now unfolding on the reef, adding to events in 1998, 2002, 2016, 2017 and 2020.
Dr David Wachenfeld, chief scientist at the Great Barrier Reef Marine Park, told Guardian Australia: “There is certainly a risk we are seeing a mass bleaching event, but we aren’t in a position to confirm that yet.
“We want to finish the aerial surveys to really understand this before we make a call on the extent and severity of this bleaching.”
Lobbying last year by the Morrison government saw the 21-country world heritage committee go against UN advice to put the reef on a list of sites in danger. The committee will consider the reef again at a meeting in June, armed with a report from the UN visit.
Aerial surveys from helicopters that started last Saturday have revealed mild to moderate bleaching driven by rising ocean temperatures on reefs in the remote far north, with the most badly hit reefs across a 250km stretch to the north and south of Townsville.
Most reefs in that central region, between Hinchinbrook Island and Bowen, were severely bleached and there were still reefs not yet surveyed there.
Bleaching is considered minor if less than 10% of corals on an individual reef are bleached. Levels up to 30% are categorised as moderate, up to 60% is major and beyond that, bleaching is considered severe.
“We certainly have widespread bleaching. It’s variable,” Wachenfeld said.
“The fact that at the very least, from Hinchinbrook to Bowen, most reefs are severely bleached – this is a very serious event. There is no question about that. Some of the observations in that region have been of coral mortality.
“That is where the heat stress has been worst. We haven’t yet surveyed all that area, but I would expect that situation of most reefs being severely bleached would go north and south of Bowen.”
Aerial surveys started while the heat stress was still building across large parts of the reef. Wachenfeld said rather than wait until the heat had peaked, the flights had started because “we are starting to see coral die.”
When a coral bleaches, the transparent flesh and white skeleton are easy to see from the air. But if it dies, the flesh begins to rot and is quickly taken over by algae which is darker in colour.
“You then can’t see from the air that a living coral was there a week ago,” said Wachenfeld.
Flights are expected to continue until the end of next week. Planes will be used to survey outer reefs in the south.
Surveys have not yet been conducted over the major tourism areas around Cairns and Port Douglas, but heat stress has been lower in those areas.
In the remote north, Wachenfeld said some reefs had not recovered from a severe 2016 bleaching event. Reports of “no bleaching” from this week’s flights were down to there being little live coral left.
Dr Britta Schaffelke, director of Great Barrier Reef research at the Australian Institute of Marine Science – a partner in the survey effort – told Guardian Australia it was too early to know how the current event compared to previous ones.
“At the moment, what we see is widespread and in some parts it is severe and that is worrying. There is no doubt about it,” she said.
While some bleached corals can recover, those badly hit can take weeks or months to die from bleaching, so the full impact of the current event will take a long time to fully understand.
“It’s a major stress event for corals even if they don’t die from it. There is no historical record of such stress events happening so frequently,” Schaffelke said.
Richard Leck, head of oceans at WWF Australia, said bleaching was directly attributable to global heating caused by rising greenhouse gas emissions.
“Reducing Australia’s domestic and exported emissions fast, this decade, is the main solution within our control,” he said.
The environment group released analysis on Friday showing that for Australia to be part of efforts to keep global heating to 1.5C, the country should release no more than 4bn tonnes of CO2 between now and mid-century.
But the analysis, carried out by scientists, said the Morrison government’s current strategy to reach net zero would release 9.6bn tonnes.
“We’re going to blow our emissions budget by more than double,” said Leck.
Dr Zebedee Nicholls, one of the scientists that carried out the analysis, said: “The science is clear: the outlook for coral reefs around the world is bad at 1.5C, and their fate is all but sealed at 2C.”
Greenpeace Australia climate impacts campaigner Martin Zavan said: “This latest bleaching event has once again exposed the Morrison government’s failure to protect the Great Barrier Reef, throwing billions at band-aid measures while failing to address climate change, the biggest driver of catastrophic coral damage.”
Kelly O’Shanassy, chief executive of the Australian Conservation Foundation, said: “If the federal government is serious about its claim of wanting to protect the Great Barrier Reef it must rapidly phase out coal, oil and gas and stop encouraging the growth of fossil fuel industries.”
Dr Lissa Schindler, reef campaigner at the Australian Marine Conservation Society, said the unfolding bleaching was “disastrous news” for the marine and communities that relied on the reef.
“What is most concerning is that this widespread bleaching is happening during a La Niña weather event, which is normally characterised by rain and cloud cover on the east coast of Australia often helping to cool waters. It shows the consistent pressure our reef is now under from global heating.”
Guardian Australia has approached the environment minister, Sussan Ley, for comment about the bleaching.
One of the world’s leading coral scientists claims a sixth mass bleaching event is unfolding across the Great Barrier Reef, with official monitoring flights now under way all along the Queensland coastline.
The Great Barrier Reef Marine Park Authority (GBRMPA) has confirmed monitoring flights are being conducted “along the length and breadth” of the 2,300km world heritage reef.
But the authority is not due to make a formal update on conditions over the reef, or the initial findings from those flights, until Friday.
The development comes less than a week before the start of a 10-day United Nations monitoring mission to the reef ahead of a crucial meeting of the world heritage committee in June.
Prof Terry Hughes, a leading expert on coal bleaching at James Cook University, said he had received a “flood of reports from the field” of bleached corals in the last two weeks.
Rising ocean temperatures driven by human emissions of greenhouse gases have caused five mass bleaching events along the reef in 1998, 2002, 2016, 2017 and 2020.
Hughes told the Guardian he believes a sixth mass bleaching event is now unfolding, and that it was not mild or local.
The amount of heat stress over the reef tends to peak in early to mid-March each year but scientists began to worry as early as December after water temperatures rose to record levels for that month.
Hughes said: “We all breathed a sigh of relief because corals that were pale in December regained their colour in January and February. But in the last three weeks there have been reports of moderate to strong bleaching all along the reef.”
Observations from the Bureau of Meteorology show water temperatures at between 1C and 2C above average across wide areas of the reef.
During the last three mass bleaching events, Hughes has led aerial surveys across the length of the marine park to record the condition of corals from a low-flying aircraft.
Hughes said that task had now been passed on to GBRMPA.
He said water temperatures and the accumulated heat stress alone was not enough to say for sure if corals had bleached.
“We won’t have a full picture until the flights are done,” he said. “We have to see those maps [of bleaching] so it is premature to say how this ranks next to the other five bleaching events.”
GBRMPA has been collating information on bleaching from flights, in-water surveillance and reports for weeks.
A week ago the authority said there had been “low to moderate bleaching” reported in many areas.
In a statement on Thursday, the authority said it was “conducting aerial surveys along the length and breadth of the reef, to get a clearer picture of any bleaching in the Marine Park this summer. The status of reef health is updated each Friday.” Flights began last weekend.
The Australian Institute of Marine Science has previously said a recovery in coral cover over the reef since the last bleaching event in 2020 has been driven by fast-growing acropora corals that were also susceptible to bleaching.
Hughes said northern parts of the reef were “halfway to recovery” but a lot of “vulnerable corals” were now bleaching.
Corals can recover from mild bleaching, but if heat stress is too severe the coral can die.
While there is no formal definition of a mass bleaching event, Hughes said: “Most people would describe bleaching that includes severe levels of bleaching at a scale of hundreds of kilometres would qualify as a mass bleaching.”
Last week, environment groups said it was vital that a UN mission to the reef – requested by Australia and starting on Monday – should be able to see bleaching.
No details have been released either by Unesco or the Australian government about where the mission will go or who it will meet.
A report from the mission is expected by early May ahead of a scheduled world heritage committee meeting in June.
Last year, UN science advisors recommended the committee place the reef on a list of world heritage sites “in danger” because of the impacts of bleaching and a lack of progress in improving pollution levels.
Australia reportedly struck at least one quid pro quo – a deal with Spain to back a world heritage inscription for a site in Madrid, despite UN advisors opposing it, in exchange for Spain’s support to block an “in danger” listing for the reef.
But many reef scientists have said efforts like finding more heat-tolerant coral species, improving water quality and removing coral-eating starfish will be overrun by global heating unless greenhouse gas emissions are cut rapidly.
