Scientists say global warming has decimated the 1,400-mile ecosystem in north-east Australia, with 30 per cent of the reef's coral dying in the heatwave from March to November 2016.
But when greenhouse gas emissions continue their existing trajectory, the reef will probably be more pliable, " also said.
Corals in Australia's Great Barrier Reef have a lower tolerance to heat stress than expected, contributing to a permanent transformation of the mix of species in some of most pristine regions, a team of global researchers has found.
Although some think the effects of climate change are hazy and yet to rear their head, it has actually been affecting the reef for at least 20 years. A study that came out just last week found that the number of ocean heatwaves has risen by more than 50% since 1925, threatening to collapse marine ecosystems all over the world.
Hughes said researchers were also surprised at how quickly some corals died in the extreme marine temperatures.
Mark Eakin of NOAA's Coral Reef Watch said that "This has really been an event that is changing the character of these reefs, and now that these marine heat waves are coming more frequently and more severely, we expect this sort of damage to keep occurring on coral reefs around the world".
As a result of the damage, the world's largest coral reef is unlikely to recover in the distant future. The new patterns of bleaching did not predict the identity of the corals that ultimately died, many corals died suddenly from heat stress, and that others died slowly following the depletion of their zooxanthellae.
Hughes and his colleagues have been directly studying this extreme die-off at the reef since its beginning during the 2016 El Nino event, when they took observations through aircraft surveys and dives, revealing scenes like this: The researchers then reported back dire dispatches about the destruction, documenting coral reefs' surprisingly immediate vulnerability to warming ocean waters. The corals that survived are "tougher", he said, than those that perished. It is a fact nearly beyond comprehension: In the summer of 2015, more than 2 billion corals lived in the Great Barrier Reef. "We need to focus urgently on protecting the glass that's still half-full, by helping these survivors to recover", Hughes said in a statement. "Our study shows that coral reefs are already shifting radically in response to unprecedented heatwaves", Professor Hughes said.
Approximately one-third of the world's coral reefs were affected by bleaching in 2016.
It garners 2 million visitors a year, supports 64,000 jobs and has contributed an estimated $6.4 billion to the Australian economy on an annual basis, according to the Great Barrier Reef Foundation.
Hughes and his team of ecologists closely examined the 2,300-kilometre Great Barrier Reef after the 2016 heatwave.
In the much warmer waters of the Red Sea, researchers at King Abdullah University of Science and Technology in Saudi Arabia have been looking at how corals can potentially adapt to increased temperatures. They shed the vibrant algae that gives them their colours and, as their algae dwindles, corals fade until they're completely white.