James Cook U. Study - Since 1998, Less Than 2% Of The Great Barrier Reef Has Not Been Bleached

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Hopes that enough of the Great Barrier Reef could escape global heating long enough for it to recover have been challenged by research finding less than 2% of its coral reefs have escaped bleaching since 1998. The world’s largest coral reef system has suffered five mass bleaching events in that time – caused by rising ocean temperatures driven by the burning of fossil fuel – which have undermined its survival. The most recent event was the most widespread yet.

In a study released on Friday, James Cook University’s Prof Terry Hughes and colleagues studied the locations of bleaching events and found only 1.7% of individual reefs had avoided bleaching. Almost all of the places that escaped damage were in an area known as Swain reefs in the southern section of the world heritage listed marine park.

Some reef experts hope cooler areas will act as refuges from bleaching, enabling corals to survive and naturally disperse their larvae on to damaged reefs. But the research in the journal Current Biology found areas “earmarked earlier as candidate refuges” had now experienced severe or moderate bleaching at least once.

“The world is now littered with former potential coral reef refuges that have since bleached,” leading reef expert Hughes said. Hughes said reefs would struggle to survive even if countries were successful in meeting pledges made at the ongoing Cop26 climate talks in Glasgow.

EDIT

https://www.theguardian.com/environment/2021/nov/05/great-barrier-reefs-future-dealt-blow-as-study-finds-only-2-escaped-coral-bleaching

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1. There is some good news in the 2020/21 condition report from Australian Institute of Marine Science

Summary

Hard coral cover increased across all three regions (Northern, Central and Southern) in the last two years, and most reefs surveyed had moderate or high coral cover.

After a decade of cumulative disturbances, the Great Barrier Reef (GBR) has experienced a low disturbance year in 2021. There was no prolonged heat stress or any cyclones of note, and decreased numbers of crown-of-thorns starfish outbreaks across much of the GBR. Results from 2021 revealed minimal loss of coral from the 2020 coral bleaching event, as only a few survey reefs experienced heat stress during 2020 above the threshold at which extensive coral mortality is expected.

While there has been recovery of hard coral cover, this was driven by fast-growing Acropora corals which are vulnerable to the common disturbances affecting the GBR. Surveys also recorded shifts in coral communities on some outer shelf reefs in the Northern and Central GBR following the 2016/17 mass coral bleaching events.

The GBR remains exposed to the predicted consequences of climate change, including more severe cyclones and more frequent and intense marine heatwaves. The observed recovery has been seen previously and can be reversed in a short amount of time.

https://www.aims.gov.au/reef-monitoring/gbr-condition-summary-2020-2021