How does coral become bleached?
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How does coral become bleached?

10 April 2017 Last updated at 16:56 BST

Two-thirds of the Great Barrier Reef in Australia has now been devastated by severe coral bleaching, according to scientists.

A new survey of the reef shows that the latest damage is mainly in the middle section. Last year, the northern parts were badly hit.

But how does coral become bleached? Watch Whitney's report.