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

Widespread bleaching during the cooler temperatures of La Nina has left scientists dreading the damage that could be caused by the next El Nino

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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.