Australia’s two world heritage-listed reefs, Ningaloo on the west coast and the Great Barrier Reef on the east, are facing simultaneous coral bleaching events, which experts have described as “heartbreaking” and a “profoundly distressing moment.” Scientists are monitoring the heat stress and bleaching across thousands of kilometres of marine habitat, likely caused by global heating.

An interactive map shows bleach alert levels on Australian coastlines, and a separate key explains the different levels of bleaching severity.

The Great Barrier Reef is experiencing bleaching from Townsville to Cape York, a stretch of approximately 1,000 kilometres. On Western Australia’s Ningaloo reef, the waters have recorded the highest heat stress levels on record, occurring during an extended marine heatwave.

Paul Gamblin, CEO of the Australian Marine Conservation Society, has highlighted that this event will be historically recorded as a time when two iconic reefs suffered simultaneous damage. Coral bleaching is caused when ocean waters become too warm, causing the loss of the algae that provide corals with their vibrant colour and nutrients. If the bleaching is not severe, corals can recover; however, studies suggest that they become less capable of reproducing and more susceptible to disease.

Scientists measure the heat stress corals face using “degree heating weeks” (DHW). Corals typically begin to bleach at around 4DHW, with 8DHW potentially leading to the death of heat-sensitive corals. On the Ningaloo coast, DHW levels have reached up to 16, the highest recorded.

Dr. Zoe Richards of Curtin University has seen firsthand the severity of the bleaching at Ningaloo, with up to 90% of corals in some areas showing signs of bleaching. Even slow-growing corals hundreds of years old are affected.

Ningaloo experienced a similar event only three years ago. The WA government has confirmed that bleaching has also been reported at other reefs, indicating a widespread impact.

Coral reef experts emphasize that the frequency and severity of these events are alarming and that stronger action on climate change is necessary to prevent further damage to these important ecosystems.

Source: https://www.theguardian.com/environment/2025/mar/23/ningaloo-and-great-barrier-reef-hit-by-profoundly-distressing-simultaneous-coral-bleaching-events