Environmental (Commonwealth Union)_ Australia’s two UNESCO World Heritage-listed coral reefs, the Great Barrier Reef in the east and Ningaloo Reef in the west, are simultaneously experiencing severe coral bleaching. Scientists monitoring these marine ecosystems describe the situation as “heartbreaking” and “profoundly distressing.”
Extensive tracking of marine heat stress indicates that rising ocean temperatures, likely driven by global climate change, are responsible for the widespread bleaching across thousands of kilometers of coral habitat. On the Great Barrier Reef, bleaching has been detected along a 1,000-kilometer stretch from Townsville to Cape York. Meanwhile, Western Australia’s Ningaloo Reef has recorded its highest levels of heat stress on record due to a prolonged marine heatwave affecting reefs across the state’s vast coastline.
Paul Gamblin, CEO of the Australian Marine Conservation Society, emphasized the historic nature of this environmental crisis. “History will remember this profoundly distressing moment when two of the world’s most famous reefs suffered catastrophic damage at the same time,” he said.
Dr. Zoe Richards, a coral scientist at Curtin University, recently spent 10 days assessing the health of Ningaloo Reef and the neighboring Exmouth Gulf. She reported that up to 90% of corals in shallow waters, including slow-growing corals that are centuries old, are severely bleached and dying. “This isn’t an isolated event it’s happening across the entire northwest shelf,” she warned. “Climate change has caught up with the reefs of Western Australia.”
The Western Australian government has confirmed reports of bleaching across Kimberley, Ashmore Reef, Rowley Shoals, Barrow Island, Dampier Archipelago, the inshore Pilbara, and Exmouth Gulf. The phenomenon marks an unprecedented scale of impact across the region.
Corals rely on symbiotic algae for their color and nutrition, but when exposed to prolonged heat stress, they expel these algae, turning white. If temperatures remain high for extended periods, corals struggle to recover, making them more susceptible to disease and reducing their ability to reproduce.
To measure heat stress, scientists use a metric known as Degree Heating Weeks (DHW). Corals typically start bleaching at 4DHW, and exposure to 8DHW can be fatal for heat-sensitive species. Oceanographer Dr. Jessica Benthuysen from the Australian Institute of Marine Science (AIMS) noted that some areas of Western Australia had recorded up to 16DHW, the highest on record. According to the U.S. Coral Reef Watch program, DHWs between 12 and 16 can cause mass coral mortality across multiple species.
The Great Barrier Reef Marine Park Authority has conducted aerial surveys across the northern reefs, revealing widespread bleaching at most sites. Underwater assessments found bleaching at 24 of the 30 reefs surveyed, with the most severe cases occurring in the northernmost regions.
Dr. Neal Cantin, a coral reef biologist at AIMS, reported significant bleaching from Cairns to the far north, where heat stress levels ranged from 6 to 13 13DHW. “These levels are capable of causing widespread coral death,” he said. Meanwhile, Dr. Roger Beeden, the chief scientist at the authority, stressed the urgency of the situation. “It’s not just the severity of these events but their increasing frequency that concerns us the most,” he stated.
Lizard Island, located in the northern Great Barrier Reef, has now experienced six consecutive summers of bleaching. Last year’s extreme heat killed one-third of the island’s live corals. This year, while the mortality rate appears lower, the devastation is still severe. “The reason there’s less coral mortality this year is that many of the sensitive species already died last summer,” explained Dr. Emily Howells, a coral scientist at Southern Cross University. “These ecosystems simply aren’t getting the recovery time they need. It’s heartbreaking.”
In addition to heat stress, heavy flooding from torrential rains has exacerbated the crisis in northern sections of the Great Barrier Reef. The TropWATER research group at James Cook University has tracked sediment-laden floodwaters spreading across 700 kilometers of coastline and extending 100 kilometers offshore. Reef water quality expert Jane Waterhouse warns that these flood plumes carry pollutants and excess nutrients that can smother corals and fuel harmful algae growth. “Muddy water reduces the sunlight corals and seagrass need to thrive, while excess nutrients encourage algae that can outcompete coral,” she said.
Scientists and conservationists have long warned that climate change, driven by human activity, is a primary threat to coral reefs. Gamblin criticized the fossil fuel industry, pointing out that companies continue pushing for new large-scale projects despite the environmental toll. “The devastation unfolding on our reefs is exactly what climate scientists have been warning us about for decades,” he said. “And yet, companies are doubling down on fossil fuel expansion in places like Scott Reef. What will our children say when they look back on this moment?”
The unfolding coral bleaching crisis underscores the urgent need for stronger climate action. Without significant reductions in global carbon emissions, marine heatwaves will continue to intensify, making it harder for reefs to recover. As scientists stress, every delay in addressing climate change brings reefs closer to irreversible collapse.
