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.
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
Graham Askew in collaboration with Bangor University, BBSRC (Mar 2017), £477,383
Stephen Muench, BBSRC (Mar 2017), £132,945
Nic Stonehouse, MRC (Mar 2017), £906,341
Bill Kunin, Steve Sait, BBSRC (Mar 2017), £602,831
Adrian Goldman, EU (Mar 2017), £546,576
Sheena Radford, Wellcome Trust (Mar 2017), £1,836,482
Beatrice Filippi, Royal Society (Mar 2017), £15,000
Jamie Johnston, Royal Society (Mar 2017), £15,000
Tom Bennett, Royal Society (Mar 2017), £15,000
Ryan Seipke, BBSRC (Feb 2017), £52,116
Mary O'Connell, BBSRC (Feb 2017), £46,986
Hannah Dugdale, NERC (Feb 2017), £504,138
Anastasia Zhuravleva, EPSRC (Jan 2017), £100,792
Richard Bayliss, Cancer Research UK (Jan 2017), £1,600,000
John Barr, EU (Jan 2017), £339,000
Mark Harris, Royal Society (Jan 2017), £250,000
Alison Dunn, NERC (Jan 2017), £105,000
Alex Breeze, Pancreatic Cancer Research Fund (Jan 2017), £180,000
Alison Dunn, NERC (Dec 2016), £18,000
Lisa Collins, BBSRC (Dec 2016), £1,681,835
Brendan Davies, Leverhulme Trust (Dec 2016), £247,555
Alan Benson, Mark Drinkhill, Ed White, British Heart Foundaion (Dec 2016), £217,223
Adrian Goldman, Royal Society (Dec 2016), £82,999
Lisa Roberts, Alex Breeze, Brendan Davies, Timothy Devinney, Oliver Harlen, Joseph Holden, Anthea Hucklesby, Pamela Jones, Philip Mellor, RCUK (Nov 2016), £484,172
Lisa Roberts, Alex Breeze, Brendan Davies, Timothy Devinney, Oliver Harlen, Joseph Holden, Anthea Hucklesby, Pamela Jones, Philip Mellor, Wellcome Trust (Nov 2016), £119,343
Katie Field, Rank Prize Funds (Nov 2016), £20,000
Jessica Kwok, Royal Society (Nov 2016), £14,948
John Ladbury, Cancer Research UK (Oct 2016), £4,250
Miriam Wittmann, Martin Stacey, Edward Vital, Lupus UK
(Oct 2016), £34,010
Valerie Speirs, NC3Rs
(Oct 2016), £90,000
Nicola Stonehouse, Morgan Herod, David Rowlands, BBSRC
(Sep 2016), £436,424
Joseph Cockburn, Wellcome Trust
(Sep 2016), £100,000
John Barr, Public Health England
(Sep 2016), £94,471
Helen Miller, DSM Nutritional Products A/S
(Sep 2016), £54,680
Steven Clapcote, Vitaflo International Ltd
(Sep 2016), £39,285
Juan Fontana Jordan De Urries
, Royal Society
(Sep 2016), £21,793
Jing Li, Sarah Calaghan, Mark Drinkhill, British Heart Foundation
(Sep 2016), £117,585
Sheena Radford, Alison Ashcroft, BBSRC (Sep 2016), £457,216
Patricija Van Oosten-Hawle, An-Jung Chen, David Westhead, NC3Rs
(Sep 2016), £354,456
Glyn Hemsworth, BBSRC (Sep 2016), £1,024,034