Unprecedented heatwave causes mass bleaching of Ningaloo, Kimberley reefs

The state government has sounded the alarm over the health of local marine ecosystems after a severe and prolonged heatwave, stating the “scale and intensity of coral bleaching has never before been witnessed in WA waters”.

The Department of Biodiversity, Conservation and Attractions first reported above-average sea surface temperatures off the coast in mid-2024.

Photos from coral bleaching along the Ningaloo coast in February.Credit: Blue Media Exmouth, Brooke Pyke

Temperatures in the north of the state continued to escalate and reached the threshold for coral bleaching in November.

Although the Kimberley region has cooled in the last month, predictive modelling by the Bureau of Meteorology suggests highly elevated temperatures will persist along the Pilbara, Gascoyne and Mid West coast into May or June.

Newly minted Environment Minister Matthew Swinbourn raised the issue in parliament this week and said the scale and duration of the marine heatwave exceeded any previously recorded conditions along the state’s coast.

He said the DBCA had conducted broadscale aerial surveys to evaluate coral bleaching across the Kimberley and Ningaloo marine parks, and in-water surveys in the marine parks between the Montebello Islands and Jurien Bay to assess the health of corals, algae, invertebrates, fish and seagrass communities.

“The scale and intensity of coral bleaching has never before been witnessed in WA waters,” Swinbourn said.

“Bleaching has not been restricted to shallow water lagoons and reef flats, but has occurred in deeper water on the outside of reefs, where bleaching is typically much less likely to occur.

“Widespread bleaching has been observed for the first time on reefs throughout the Kimberley, which are considered to be among the most heat tolerant in the world.”

Swinbourn said the effects of “increasingly frequent, widespread and intense marine heatwaves” were unlikely to be limited to coral reefs, and that ongoing monitoring was needed to identify further impacts.

“Marine heatwaves do not recognise boundaries of marine parks and protected areas, but active adaptive management of these areas can increase resilience by reducing other pressures that marine habitats and wildlife might face,” he said.

“Protections afforded by our marine parks give wildlife and ecosystems the best chance of bouncing back.”

Australian Institute of Marine Science coral reef scientist Dr James Gilmour said WA had recorded severe bleaching events before, but this was the first time so many different reefs had bleached in the same year.

He said the marine heatwave had reached unprecedented levels through December 2024 and January 2025.

“The heat stress was unique in its timing for this region, arriving months before peak heat stress is anticipated for Western Australian reefs – typically in March or April,” he said.

“It can take 10 to 15 years for severely bleached reefs to recover.”

He said during recent field trips to the Rowley Shoals and to Ashmore Reef, he had seen the bleaching and mortality, but the team needed to analyse the data further to understand the details.

Gilmour said globally, climate change remained the biggest threat to coral reefs, causing more frequent and severe marine heatwaves and shortened windows of recovery.

“We need marine science to develop interventions that can help,” he said.

Greens WA fossil fuel and climate change spokeswoman Sophie McNeill said Swinbourn’s statement was “devastating for all Western Australians who love our oceans, our reefs and our beautiful marine life”.

“This is exactly what climate scientists have warned of for decades if governments did not start to phase out fossil fuels,” she said, before criticising the state government’s response to the problem.

She said they had been “adding fuel to the underwater fire raging off our coasts by approving massive new gas projects”.

“How many coral bleaching events will it take. How many unprecedented and never before seen climate impacts do we have to witness before WA Labor takes steps to reduce emissions,” McNeill said.

“Our reefs are bleaching now. Our oceans are boiling now. We simply cannot afford any more climate inaction.”

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