‘Deathly silent’: two out of three corals in world heritage-listed Ningaloo reef have been killed, scientists confirm | Ningaloo reef

Almost two in three corals at popular tourist spots on the world heritage-listed Ningaloo Reef have died following an unprecedented marine heatwave affecting the Western Australian region, scientists said.

Areas in Ningaloo’s northern lagoon had undergone “profound ecological simplification”, with coral species – the cornerstones of habitat – among those killed.

A marine heatwave ravaged the Western Australian coastline last summer and autumn, turning corals from Ningaloo to Ashmore reefs 1,500km to the northeast turning white from heat stress.

When corals stay in unusually hot water for too long, they break away from the algae that give them most of their color and nutrients, leaving behind a translucent flesh that reveals the white skeleton.

Approximately 90% of the extra heat on the planet is absorbed by the oceans. Warming is caused by greenhouse gases released by burning fossil fuels and cutting down forests.

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Coral scientist Zoe Richards, associate professor at Curtin University, surveyed 1,600 individual corals across eight 40km sites during the peak of the bleaching event in March.

“The bleaching was very confronting because it was so broad,” he said.

Other scientists who visited Ningaloo during the mass coral bleaching spoke of their shock at the extent of the heat and the suffering of the corals.

When Richards, who carried out the study in partnership with Minderoo Exmouth Research Laboratory, returned at the end of October with Curtin University researcher David Juszkiewicz, about 1,000 of the 1,600 corals he recorded were dead.

He said: “You would hope that the partially bleached corals you see would be able to recover. Unfortunately the scales have tipped towards mortality. Most of the data shows that corals that are bleached in March die later.”

‘Incredible places’

Richards said the areas examined were between the Osprey and Tantabiddi sacred sites and included northern parts of the Ningaloo lagoon popular with tourists.

“These are incredible places where you can swim right off the coast and see all these luxurious corals,” he said.

Diving and snorkeling on these reefs is often accompanied by “lots of popping and popping” sounds from fish and other animals, Richards said.

“It was dead silent,” he said. “The only animals that looked happy were the sea cucumbers. They’re detritus eaters.”

Richards said corals in neighboring Exmouth Bay were doing much better, but the northern Ningaloo areas studied were experiencing “profound ecological simplification” with “a marked loss of biodiversity and reduction in habitat complexity”.

“There are some resilient corals out there, but they are only a small fraction of the diversity that was there before,” he said.

“These corals provided habitat for the fish, crabs and molluscs that lived among them.

“This means ecological extinction of corals, but what other co-extinctions could be occurring at the same time? We don’t have data on that.”

Fourth mass whitening

Coral loss at Ningaloo was part of the fourth and worst recorded global mass bleaching event, which left more than 80% of reefs in more than 80 countries exposed to temperatures high enough to cause bleaching.

Some scientists have argued that global warming has already pushed tropical coral reefs into long-term decline.

“Corals act as thermometers for the ocean,” Richards said.

“When they bleach, they send a clear signal that the temperature is too high. They don’t speak, but they signal to us very clearly. We are on the verge of a catastrophic ecosystem collapse. It’s happening everywhere.”

“It’s really depressing. I’ve dedicated my whole life to coral research. I’m starting to envision the point where all that’s left of corals and reefs are memories.”