Here we present the added value of a regional climate simulation, performed with the regional Coupled-Ocean–Atmosphere-Wave-Sediment Transport model COAWST, centered over the Caribbean – one of the first of its kind on a climatological scale. There is an urgent need to improve capacity to predict marine heatwaves given their substantial negative impacts on marine ecosystems. This suggests that WA reefs are now at risk of severe bleaching during both El Niño and La Niña years. The only other major mass bleaching in WA occurred during a strong La Niña event in 2010/11 and primarily affected reefs along the central-to-southern coast. Some heat stress (2.4 DHW) and bleaching (<30%) also occurred at Rottnest Island (32☀1'S), whereas coral communities at Ningaloo Reef (23☉'S) and Bremer Bay (34☂5'S) were not impacted. The heatwave primarily affected the macrotidal Kimberley region in northwest WA (∼16°S), where 4.5-9.3 degree heating weeks (DHW) resulted in 56.6-80.6% bleaching, demonstrating that even heat-tolerant corals from naturally extreme, thermally variable reef environments are threatened by heatwaves. Here we report the first El Niño-related regional-scale mass bleaching event in WA. Coral health surveys were conducted during the austral summer of 2016 in four bioregions along the WA coast (∼17 degrees of latitude), ranging from tropical to temperate locations. This event impacted coral reefs around the world, including in Western Australia (WA), although WA reefs had largely escaped bleaching during previous strong El Niño years. In 2015/16, a marine heatwave associated with a record El Niño led to the third global mass bleaching event documented to date.
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