Terry Hughes, Britta Schaffelke and James Kerry write in The Conversation (29.11.16):
'Two-thirds of the corals in the northern part of the Great Barrier Reef have died on in the reef’s worst-ever bleaching event, according to our latest underwater surveys.
'On some reefs in the north, nearly all the corals have died. However the impact of bleaching eases as we move south, and reefs in the central and southern regions (around Cairns and Townsville and southwards) were much less affected, and are now recovering.
'In 2015 and 2016, the hottest years on record, we have witnessed at first hand the threat posed by human-caused climate change to the world’s coral reefs.
'Heat stress from record high summer temperatures damages the microscopic algae (zooxanthellae) that live in the tissues of corals, turning them white. After they bleach, these stressed corals either slowly regain their zooxanthellae and colour as temperatures cool off, or else they die.
'The Great Barrier Reef bleached severely for the first time in 1998, then in 2002, and now again in 2016. This year’s event was more extreme than the two previous mass bleachings.'