Australia’s Great Barrier Reef has suffered its most widespread coral bleaching on record, scientists said today in a dire warning about the threat posed by climate change to the world’s largest living organism.
James Cook University’s Professor Terry Hughes said a comprehensive survey last month found record sea temperatures had caused the third mass bleaching of the 2300-kilometre reef system in just five years.
Bleaching occurs when healthy corals become stressed by changes in ocean temperatures, causing them to expel algae living in their tissues which drains them of their vibrant colours.
“We surveyed 1036 reefs from the air during the last two weeks in March to measure the extent and severity of coral bleaching throughout the Barrier Reef region,” Professor Hughes said.
“For the first time, severe bleaching has struck all three regions of the Great Barrier Reef, the northern, central and now large parts of the southern sectors.”
The damage came as February brought the highest monthly sea temperatures on the Great Barrier Reef since Australia began keeping records in 1900.
Professor Hughes has released maps showing severe levels of bleaching occurred in 2020 in all three sections of the reef, northern, central and southern, the first time this has happened since mass bleaching was first seen in 1998.
Professor Hughes said severe mass bleaching had never before hit the southern section of the reef, from Mackay south.
That area had high numbers of heat-sensitive corals that “light up like a Christmas tree” when viewed from the air.
“It’s not too late to turn this around with rapid action on emissions,” he said.
“But business-as-usual emissions will make the Great Barrier Reef a pretty miserable place compared to today.”
The reef is worth an estimated $4 billion a year in tourism revenue for the Australian economy, but is at risk of losing its coveted UNESCO World Heritage status because warmer oceans brought about by climate change have damaged its health.
Back-to-back bleaching events in 2016 and 2017 prompted the Australian government agency overseeing the reef to downgrade its long-term outlook to “very poor”.
Bleaching was first seen on the reef in 1998, at the time, the hottest year on record, but as temperature records continue to tumble its frequency has increased, giving coral less time to recover.
James Cook University’s Professor Morgan Pratchett said although bleaching did not necessarily kill all corals, some were expected to fare worse than others.
More than half of shallow-water corals in the reef’s northern reaches died in the 2016 bleaching.
“We will go back under water later this year to assess the losses of corals from this most recent event,” Professor Pratchett said.
Dr David Wachenfeld, chief scientist at the Great Barrier Reef Marine Park Authority, said: “My greatest fear is that people will lose hope for the reef. Without hope there’s no action.
“People need to see these bleaching events not as depressing bits of news that adds to other depressing bits of news.
“They are clear signals the Great Barrier Reef is calling for urgent help and for us to do everything we can.”
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One Response
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