Coral researchers including two experts from the University of Leeds are now carrying out new aerial and underwater surveys along the Great Barrier Reef and elsewhere in Australia as bleaching reappears again this year.
The Great Barrier Reef is built by corals, a diverse group of marine invertebrates which form the reefs. The corals have been heavily bleached three times since records began in the 1980s, each time worse than the last.
The most recent bleaching was in 2016, when 85 per cent of reefs were damaged.
Bleaching is caused by thermal stress – high water temperatures during marine heatwaves – which disrupts the relationship between corals and the algae living within them. This causes the coral to lose its colour, leaves it physiologically damaged and can result in its death.
They say rising sea surface temperatures due to global warming have triggered unprecedented mass bleaching of corals.
“The severity of the 2016 bleaching was off the chart,” said lead author, Professor Terry Hughes from the Australian research Council Centre of Excellence for Coral Reef Studies at James Cook University in Australia.
“It was the third major bleaching to affect the Great Barrier Reef, following earlier heatwaves in 1998 and 2002. Now we’re gearing up to study a potential number four.”
Hotter than usual water caused by global warming was the main cause of bleaching, and Dr Beger said this latest warning on the dangers of global warming highlighted the risks of repeated exposure to unusually hot conditions.
“The Great Barrier Reef is one of the most outstanding phenomena of the natural world,” she said. “We now have evidence global warming is the leading threat to its continued existence.
"The coral supports hundreds of thousands of life forms including fish, but most of it will die by the time my kids are my age without action by governments and business to reduce global warming.”
Professor Hughes added: “It broke my heart to see so many coral dying on northern reefs on the Great Barrier Reef in 2016. With rising temperatures due to global warming, it’s only a matter of time before we see more of these events.”
Although there have been gaps of several years between past bleaching events, it has already started to be detected this year, less than 12 months after the last occasion, and Professor Hughes added: “A fourth event after only one year would be a major blow to the reef”.
The research team said while some studies had indicated prior exposure to bleaching could create resistance in corals to future incidents, their analysis of 171 sites showed it did not lessen the severity of the damage in the 2016 bleaching.
Their study did find that storms and cyclones could be a bonus for heat affected coral by cooling the seas, reducing the impact of rising temperatures.
Tropical cyclone Winston cooled the southern section of the Great Barrier Reef by around three degrees Celsius when it passed over in March 2016, meaning corals in those areas which had started to bleach recovered more quickly, while those in the northern section of the reef continued to bleach.
The study also reveals that protecting reefs from fishing, and improving water quality, makes no difference to the amount of bleaching during extreme heatwaves, although it might help them recover in the longer term.
The reality of warming oceans means that coral bleaching is the new normal and threatens reefs on a global scale, the research paper states.
Helen Miller, Innovate UK (Apr 2018), £999,960
Elisabetta Groppelli, David Rowlands & Stanley Lemon (University of North Carolina), Medical Research Foundation Fellowship (Apr 2018), £293,494
Nikesh Patel, Medical Research Foundation fellowship (Apr 2018), £290,976
Jessica Kwok & Ralf Richter, Leverhulme Trust (Apr 2018), £298,273
Julie Aspden, Royal Society (Apr 2018), £20,000
Liz Duncan, Royal Society (Mar 2018), £14,602
Alex O'Neill & Ryan Seipke, BBSRC (Feb 2018), £45,489
Jim Deuchars, Royal Society (Feb 2018), £16,300
Stefan Kepinski & Netta Cohen, Leverhulme Trust (Feb 2018), £320,387
Lisa Collins, BBSRC (Feb 2018), £49,950
Lars Jeuken, BBSRC (Feb 2018), £30,000
Nikita Gamper, BBSRC (Feb 2018), £30,000
Alison Baker, BBSRC (Feb 2018), £30,000
Scott Bowen, Leducq Foundation Grant (Feb 2018), £28,470
Jessica Kwok and Ronaldo Ichiyama, International Spinal Research Trust (Feb 2018), £94,450
Alex O'Neill, Oxford Drug Design (Jan 2018), £86,098
Dave Lewis and Colleagues in South Africa, HEFCE Global Challenge Research (Jan 2018), £48,000
Sarah Calaghan, Ed White, John Colyer, Isuru Jayasinghe, BHF (Jan 2018), £128,308
Christine Foyer and Alison Baker, HEFCE GCRF Grant (Jan 2018), £71,158
Alison Baker, Yun Yung Gong and Lindsay Stringer and ICRISAT India, HEFCE GCRF Grant (Jan 2018), £27,000
Graham Askew, Simon Walker, BBSRC (Jan 2018), £699,781
Jennifer Tomlinson, Royal Society (Jan 2018), £512,801
Alison Dunn, NERC (Dec 2017), £18,000
Jennifer Tomlinson, Royal Society-Research Fellows Enhancement Award (Dec 2017), £94,681
Helen Miller, AB AGri Grant (Dec 2017), £73,600
Simon Walker, Royal Society Enhancement Award (Dec 2017), £10,000
Carrie Ferguson, Bryan Taylor, Harry Rossiter, The Physiological Society (Dec 2017), £7,392
Ralf Richter, Royal Society (Dec 2017), £6,000
Christine Foyer, British Council Newton Fund (Dec 2017), £49,840
Adrian Whitehouse and colleagues in School of Chemistry and University of Liverpool, MRC (Nov 2017), £622,319
Michelle Peckham, Neil Ransom, MRC (Nov 2017), £495,159
Dave Lewis, British Council India (Nov 2017), £22,540
Elton Zeqiraj, Royal Society (Nov 2017), £15,000
Hannah Dugdale, Royal Society (Nov 2017), £15,000
Shaunna Burke, Cancer Research UK Innovation Grant (Nov 2017), £20,000
Alex O'Neill and colleagues in Chemistry, BBSRC (Nov 2017), £431,865
Jessica Kwok, Wings for Life (Nov 2017), £87,365
Tom Bennett, BBSRC (Oct 2017), £523,679
Neil Ranson, Darren Tomlinson, BBSRC (Oct 2017), £494,318
Nikita Gamper, BBSRC (Oct 2017), £490,426
Amanda Bretman and colleagues from UEA, NERC (Oct 2017), £430,886
Juan Fontana, Rosetrees Trust consumables grant (Oct 2017), £22,500
Helen Miller, DSM Nutritional Products AG (Sep 2017), £69,988
Neil Ranson, Juan Fontana, Mark Harris, Michelle Peckham, Ralf Richter, Peter Stockley, Patricija Van Oosten-Hawle and colleagues in Engineering, FMH and MAPS, Wellcome Trust Equipment Call (Sep 2017), £418,000
Jamie Johnston, Physiological Society (Sep 2017), £10,000
Frank Sobott, Adrian Goldman, Mark Harris, Andrew Macdonald, Stephen Muench, Sheena Radford and colleagues in FMH and MAPS, Wellcome Trust Equipment Call (Aug 2017), £415,000
Ralf Richter, David Brockwell, Eric Hewitt, Jessica Kwok, Emanuele Paci and MAPS/FMH, BBSRC (Jun 2017), £600,000
Eric Blair, Adrian Whitehouse, Nicola Stonehouse, Alison Baker, Richard Bayliss, Joan Boyes, Ryan Seipke, Sally Boxall and MAPS/FMH, BBSRC (Jun 2017), £376,000
Stefan Kepinski, Yoselin Benitez-Alfonso, Tom Bennett, Michelle Peckham, BBSRC (Jun 2017), £331,000
Roman Tuma, Lars Jeuken, Paul Millner, Sheena Radford, Peter Stockley and MAPS/FMH, BBSRC (Jun 2017), £222,000
Vas Ponnambalam, Darren Tomlinson, Stephen Wheatcroft, BHF (May 2017), £107,878