Coral Bleaching Currently Affecting 91 Percent Of The Great Barrier Reef


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer


This is the first time mass bleaching has occurred during a La Niña, proving that no year is safe. Image credit: Ethan Daniels/  

A report quietly released by the Great Barrier Reef Marine Park Authority (GBRMPA) has revealed that 91 percent of individual reefs in one of the wonders of the world were affected by bleaching last summer. Although the proportion is lower at the organism level, and some of them will recover, the report is shocking because this should have been a year for regrowth, not further setbacks.

Last year the world experienced a major La Niña event, which means heavy rains along Australia's east coast. That brought devastating floods to much of the region, including cities that suffered a “one in a hundred-year” flood a month after a “one in five hundred years” disaster. However, one morsel of compensation was the anticipated respite for the western Pacific's coral reefs, whose primary threat is the heat associated with El Niño events.


It hasn't turned out that way. For months marine biologists have been sounding warnings of the tell-tale white patches that appear when corals get stressed and expel their symbiotic microalgae. However, results of GBRMPA's annual survey of the reef as a whole have been kept quiet, leading to allegations their release was being delayed until after the Australian federal election on May 21 to avoid embarrassing the government.

The report was released without the usual publicity, but was picked up by The Guardian.

Whether or not reports of pressure for delay are true, there is no question this isn't news the governing coalition would have wished anyone to hear before voting. “The surveys confirm a mass bleaching event, with coral bleaching observed at multiple reefs in all regions,” a statement accompanying the report said

This is the sixth known mass bleaching event, all in the last 25 years, and the fourth since 2016. It's also the first time mass bleaching has occurred during a La Niña, proving that no year is safe.


Even when corals survive a mass bleaching event, which can happen when temperatures drop quickly enough for them to replenish themselves with new symbionts, the event takes its toll, leaving corals more vulnerable to future threats. As such, the next hot summer could mark the death knell for most of the reef, taking with it extraordinary numbers of species found nowhere else, and tourist and fishing industries worth tens of billions of dollars a year.

Scientists looked at 719 of the 3,000 designated reefs in the system, and found bleaching on 654 of them. At the northern and southern ends much of this was moderate (meaning less than 30 percent of the coral on the reef bleached) and some qualified as mild. However, the center of the reef, from the Whitsundays to near Port Douglas the impact has been apocalyptic. Almost every reef surveyed there has suffered at least 30 percent bleaching, and in most cases it is over 60 percent. This includes the major tourist areas, since at the northern end lacks facilities, and most of the southern reef is a long way offshore.

Although the report's authors have not been available for comment, Professor Terry Hughes of James Cook University has not been so reticent. Hughes, who founded the survey and led it for many years before passing it over to be jointly run by GBRMPA and the Australian Institute of Marine Science, expressed himself on Twitter.


Many factors, including over-fishing, nutrient run-off, and storms can add to the damage to coral reefs, but marine biologists agree rising temperatures and ocean acidification are the primary threats. Both are caused by the burning of fossil fuels, a fact the government – and Australia's largest media outlets – have been keen to avoid discussing, particularly while so much coal is exported through the reef.


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