There is unprecedented dying of Great Barrier Reef in the past years, with 50% mortality of the reef due to coral bleaching. Recent work on the Great Barrier Reef (GBR) indicates widespread disease, pollution, and bleaching of coral has led to more than half of the coral dead or dying to date.

Corals live in symbiosis with microalgae, called zooxanthellae, which provide the coral with nutrients and their incredible colors. When the surrounding waters become too warm, diseased, or polluted the zooxanthellae leave the corals. This leaves the corals bleached white and with little to no nutrients, hence the term coral bleaching. This does not kill the coral but leaves it in a weakened and stressed state. Eventually bleached corals can bring in new zooxanthellae but the environmental conditions have to swing back into balance before that is likely to happen.

Eventually, without the symbiotic relationship of the zooxanthellae, corals are overwhelmed by brown-green algae and other organisms and will die. Thankfully the southern hemisphere winter is coming to an end, bringing cooler temperatures that will stave off coral bleaching at least for a few months.

“This is the worst coral bleaching episode in Australia’s history, with reports of coral dying in places that we thought would be protected from rising temperatures.” – Ove Hoegh-Guldberg, University of Queensland Global Change Institute Director Professor, said in a statement to the University of Queensland press.

There have been only a handful of major bleaching events in the Great Barrier Reef's 8000-year existence. They first emerged in the early 1980s, with the 1998 and 2002 events regarded by scientists as the worst.
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At least until this latest one.

This time more than 1000 kilometres of reef has been subjected to some extent of bleaching. The pristine northern stretches between Cooktown and the Torres Strait have been hit the hardest, with images emerging of ghostly white reefs from places such as Lizard Island.

The event's spread and intensity has again raised uncomfortable questions about the damage climate change is doing to Australia's most important natural tourism site.

Professor Ove Hoegh-Guldberg, a prominent marine scientist who has studied coral reefs for decades, says he has little doubt about what is behind the bleaching.

"This event, I would say with 99 per cent certainty, is being driven by anthropogenic climate change," he says