How a marine heatwave is threatening Australia's spectacular coral reefs

The Guardian

3 days ago

When it comes to coral, the Great Barrier Reef steals the global limelight. It's a bucket-list place for many and, when it gets hit by coral bleaching, it makes news around the world.
But Australia has another group of spectacular reefs on the west of the continent. Many of them had managed to escape the worst of global heating, until the worst marine heatwave ever recorded for this region. Even a 'hope spot' for coral reefs has been decimated by the most severe heatwave on record for that part of the world.
I've been following the fate of the reefs on both coasts over recent months, and for today's newsletter I'll try to make some sense of it – after the most important reads of the week.
When you're the biggest living structure on the planet, it's not surprising you would hog the headlines. When the climate crisis is putting you under pressure, you light up like a million raised white flags to let the world know you're in trouble.
The Great Barrier Reef (GBR), on Australia's Queensland coast, is bigger than Italy and home to thousands upon thousands of species of fish, coral, molluscs and other amazing stuff.
This Australian summer, parts of the reef saw mass coral bleaching for the sixth time since 2016. We learned last week that the bleaching the previous summer – the worst on record there – drove the biggest annual drops in coral cover since detailed monitoring started in the mid-1980s.
But on the opposite side of the vast continent, Western Australia (WA) has its own World Heritage-listed reef at Ningaloo, famed for its corals and whale sharks. And just like the GBR might overshadow Ningaloo on the name-recognition stakes, so does Ningaloo overshadow Western Australia's other remote and largely pristine coral reefs.
Most of WA's reefs had escaped major heat stress events, at least until the 'longest, largest and most intense' marine heatwave ever recorded in the state's waters started to unfold around September 2024.
This week, marine scientists from government agencies and universities revealed the most comprehensive assessment yet of the known impacts of that heatwave. From Ningaloo north, reefs saw between 11% and more than 90% of their corals hit by bleaching, and death on systems as far as 1,500 km apart (for UK readers, that's farther than driving from Land's End to John o'Groats or, for American subscribers, a few hours farther than a drive from New York to Chicago).
Scientists found hardly any live corals on three remote but spectacular reefs at Rowley Shoals. The shoals, more than 1,000 km from Darwin in the Northern Territory, are described by some as one of the world's greatest diving spots. Scientists speak of them with reverence. With their steep drop-offs and sandy-bottomed lagoons covered in corals and teeming with life, they had been a 'hope spot' for marine scientists because they had been largely untouched by the rising ocean heat that has hit most of the world's reefs. Until now.
Australia's reefs are not the only ones suffering. Reefs elsewhere are also in the midst of an ongoing global bleaching event that has caused enough heat to bleach more than 80% of reefs in more than 80 countries since it started in January 2023.
How, or if, these reefs recover is an open question. Corals are complex animals, and the reefs they make with their skeletons in tropical waters are some of the richest places, in biodiversity terms, on the planet. They make up less than 1% of the ocean floor, but are home to about a quarter of marine life. They support the lives and livelihoods of hundreds of millions of people.
Previous work published by the UN's Intergovernmental Panel on Climate Change has warned that if global temperature increases hit that famous 1.5C increase, then 70% to 90% of tropical reefs will disappear.
The reality is likely more complicated. Scientists are still learning about how much capacity corals have to acclimatise, and are still understanding how reef systems will respond depending on their size, location and other pressures such as fishing and pollution.
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What solutions might there be? There's the obvious one: get greenhouse gas emissions down as low as possible, as fast as possible.
And there are a suite of more direct efforts, from developing more heat-resistant corals and 'restoring' reefs by planting out more heat-tolerant species, to brightening clouds to shade reefs, to improving local conditions to make corals as resilient as possible.
None of the coral scientists I've spoken to argue that any of these steps are a substitute for climate action, and there's a live debate among them about the wisdom of some of these interventions.
The lowest-risk approach for averting an ecosystem collapse remains tackling global heating. Without it, the surviving corals will keep raising the white flag of alarm.
Read more:
WA's 'longest and most intense' marine heatwave killed coral across 1,500km stretch
'If the reef had a voice, it would sing': could legal personhood help the Great Barrier Reef?
Fears for South Australia's annual cuttlefish gathering amid deadly algal bloom
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