Coral reef bleaching hits 84% worldwide, worst on record, surveys show / World's reefs under threat as coral bleaching intensifies / Tracing the worst coral bleaching event in recorded history - video / Ningaloo and Great Barrier Reef hit by 'profoundly distressing' simultaneous coral bleaching events / 'Catastrophic': Great Barrier Reef hit by its most widespread coral bleaching, study finds / Coral bleaching on Great Barrier Reef reaches 'catastrophic' levels / Global coral bleaching event biggest on record: US agency / Coral bleachings devastate Bali reefs as sea temperatures rise / 'Most of it was dead': scientists discovers one of Great Barrier Reef's worst coral bleaching events / Future risk of coral bleaching set to intensify globally, researchers say