Year Two Of GBR Bleaching Moving South; "The Corals Didn't Get Any Respite At All"
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Professor Hughes and his team completed aerial surveys last Wednesday after scoring about 800 separate reefs. The 8000km journey closely followed the path of the 2016 survey that found the northern regions of the Great Barrier Reef most affected. This year, the worst of the bleaching is further south in the popular tourist sector between Townsville and Cairns. (See map below.)
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Corals bleach when temperatures exceed tolerance levels for too long, prompting them to expel the algae that supply most of their energy and the brilliant colours. Not all bleached corals die but as much as two-thirds of north corals have succumbed.
"The mortality in the central region will continue to unfold over coming months," Professor Hughes said. "We've already seen substantial mortality, up to 50 per cent on some central reefs in the past six weeks." Bleaching has returned even to some of the regions hard hit last year, such as Cape York's Princess Charlotte Bay.
Some 30 reefs in the north had no score as they "effectively have ceased to exist at least in the shallow sections as coral reefs", said James Kerry, a marine biologist from James Cook University who also took part in the survey.
While this year's event is not expected to result in as much coral mortality as in 2016, there are worrying signs corals bleached at lower temperatures than a year earlier. That result may point to more bleaching next summer if conditions are again relatively warm.
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http://www.smh.com.au/environment/climate-change/huge-blow-backtoback-bleaching-covers-twothirds-of-the-great-barrier-reef-20170406-gvewah.html
