Perth Symposium gathers experts to discuss Western Australia’s worst coral bleaching event on record

With the Western Australian community deeply invested in their marine environment, from conservation through to ecotourism and recreation, the marine heatwave that has caused widespread coral bleaching and mortality off the WA coastline is of significant concern.

Following the long lasting and widespread marine heatwave, the Australian Institute of Marine Science (AIMS) is describing it as the “worst bleaching event on record for WA coral reefs”.

More than 120 experts including marine park managers, researchers, policy makers and Traditional Owners attended the Marine Heatwave Symposium in Perth on 12th August held during National Science Week to discuss the marine heatwave that has caused widespread coral bleaching and mortality off the WA coastline.

The Marine Heatwave Symposium at the University of Western Australia's Indian Ocean Marine Research Centre was coordinated by AIMS and the Western Australian Government.

It is the first time experts have come together in one location to share learnings from the monitoring and research that is underway for the current event.

Members of the WA Coral Bleaching Group, which is convened by AIMS, first began monitoring the marine heatwave in September 2024. Heat stress sufficient to cause coral bleaching peaked in December 2024/January 2025, followed by a slight easing with a late monsoon, and another peak in March/April 2025. Temperatures only began to recede in May.

AIMS senior research scientist Dr James Gilmour said the intensity of the event had been relentless with the marine heatwave impacting reefs that had previously escaped bleaching.

Dr Gilmour noted “there has been little reprieve this time for any of our northwest reefs. Areas which had given us hope because they’d rarely or not bleached before like the Rowley Shoals, north Kimberley and Ningaloo have been hit hard this time. Finally, climate heating has caught up with these reefs.”

While the full impact of the coral bleaching will take months to be known, experts from multiple organisations and agencies which make up the WA Coral Bleaching Group have so far reported bleaching and mortality ranging from medium (11%-30%) to extreme (>90%) levels across systems up to 1500km apart as a result of the marine heatwave.

Dr Gilmour added “The length and intensity of the heat stress, and its footprint across multiple regions, is something we’ve never seen before on most of the reefs in WA. For individual coral reefs we are still crunching the numbers around Degree Heating Weeks (DHW) – a measure of heat stress on corals - but early estimates are over 15 DHWs on all reefs and up to 30 DHWs at some Pilbara reefs. Eight DHWs is the level of heat stress we generally consider severe enough to cause coral mortality.”

AIMS coral scientist Nicole Ryan, who coordinates the WA Coral Bleaching Group shared “The heat stress will beat records set during the 2011 La Nina and the 2016 El Nino on all but the southernmost reefs, in the south of Ningaloo, Shark Bay and the Abrolhos Islands.

“It will take several months to understand how much this year's event will have impacted coral cover on various systems. A bleached coral is not a dead coral – it can recover.

"For some coral species, it can take time after bleaching for it to recover or die. WA reefs are also spread across thousands of kilometres with many being remote, making them difficult to monitor.”

Western Australian Environment Minister Matthew Swinbourn opened the symposium, highlighting the government's strong support for long-term marine ecosystem monitoring and management programs.

The symposium's program included presentations on oceanography and climate, as well as impacts on coral and seagrass communities delivered by experts from the Department of Biodiversity, Conservation and Attractions, the Department of Primary Industries and Regional Development, AIMS, CSIRO, the Bureau of Meteorology, the Department of Energy and Economic Diversification and university researchers.

Minister Swinbourn advised "The Western Australian community is deeply invested in our marine environment, from conservation right through to ecotourism and recreational amenity.

"The information shared at the symposium will improve overall understanding of the marine heatwave event and help prioritise the next steps in monitoring, research and future management.

"Long-term marine park monitoring programs can provide important and early insights into the impacts and recovery of marine ecosystems from environmental events, as well as human-induced activity.”

Dr Gilmour highlighted “this huge WA bleaching event comes at a concerning time for coral reefs in Australia. It was synchronised with another mass bleaching event on the Great Barrier Reef and is part of the ongoing fourth Global Coral Bleaching Event, which began in 2023 and has circumnavigated our oceans in a wave of coral mortality. Climate change is driving these events, which are becoming more frequent, more intense and more widespread, giving our amazing, valuable coral reefs little time to recover. And they need 10 to 15 years to recover fully. 

“The key to helping coral reefs survive under climate change is to reduce greenhouse gas emissions. Good management of local issues like water quality and overfishing and using interventions developed by marine science to help reefs will also assist.”

Image top. Coral bleaching at Ningaloo Credit: Declan Stick/ AIMS; image below: surveying bleached corals at Tantabiddi reef Ningaloo. Credit Declan Stick/ AIMS