Coral bleaching ? The picture's not black and white

Planet Earth -

Problems with how scientists communicate with the media and in how reefs' health is assessed have created a skewed public understanding of coral bleaching, according to a new study.

Coral bleaching is a widespread phenomenon in which corals lose their vivid colours. It's a major concern to conservationists, as it can be triggered by rapid environmental change and sometimes presages the death of whole reefs, along with the complex ecosystems they support.

But the researchers suggest we need to take a more complex view of the matter - bleaching isn't always a bad thing. 'We go out to Indonesia twice a year, and in spring when the waters are warmest the reefs are always bleached,' says Dr David Suggett, a marine biologist at the University of Essex's Coral Reef Research Unit and co-author of the paper, published in Global Change Biology.

'By summer when water temperatures are coolest they're always looking as vibrant as ever,' he adds. 'They bleach for their own benefit, to help them adapt to normal changes in their environment. This year we had the largest temperature anomaly on record in the region, but as far as we know the reefs still did incredibly well.'

Suggett and co-author Dr David Smith, also of Essex, point out that corals go through natural periods of bleaching, and that many aren't fatal. While sometimes bleaching really does herald mass coral die-offs, far more often it's just a precautionary response to natural changes in conditions. At other times, corals lose their colour due to unusual environmental stress, but recover as conditions return to normal - the researchers call this 'sub-lethal' bleaching.

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