‘It’s not supposed to be white’: one of the Great Barrier Reef’s healthiest reefs succumbs to bleaching

Dr Adam Smith dives among ‘stressed and white’ coral on John Brewer Reef off the Townsville coast in Queensland. Photograph: Harriet Spark

Through a snorkel mask, the corals struggling for survival in the heat are easy to spot. Some have turned white while others are pouring out a fluorescent pigment into their flesh – it’s spectacular, but it’s also a sign of a coral in deep distress.

This is John Brewer Reef about 70km off Townsville in Queensland – the centre of a widespread coral bleaching event. For hundreds of kilometres in either direction, reefs are going through the same battle.