Global Warming

Great Barrier Reef coral bleaching more widespread than first thought

New aerial surveys have found the devastating coral bleaching event hitting the Great Barrier Reef has a larger footprint than initially thought.

Professor Terry Hughes, who is part of a national coral bleaching taskforce, said research flights on Wednesday between Townsville and Cairns had observed differing levels of bleaching across all 74 reefs that had been surveyed in the region.

That comes on top of the significantly more severe bleaching seen further north on more than 500 reefs surveyed by plane and helicopter last week along a 1000 kilometre stretch from Cairns to the Torres Strait.

"When we initially headed north from Cairns we thought we would encounter a southern border [of the bleaching event] and beyond that in the far north things would get bad," Professor Hughes said. "We still haven't found the southern border. We will find it. It is just taking longer than we expected because the footprint of this is substantially bigger than was initially reported."

Professor Hughes said on the 74 reefs surveyed on Wednesday corals were on average bleached by about 25 to 30 per cent.

Those results are less severe than what has been seen on the reefs north of Port Douglas, where Professor Hughes said the average bleaching was closer to 75 per cent.

In total, Professor Hughes said half the Great Barrier Reef had been severely bleached in the event.

The National Coral Bleaching Taskforce has found record levels of bleaching on the Great Barrirer Reef. An aerial survey photo of a reef in the northern stretches of the Great Barrier Reef last week where the bleaching is most severe. The Great Barrier Reef Marine Park Authority last week reported coral death rates of 50 per cent on the reefs in the inner Cape York region.

Professor Hughes said it was known there was no bleaching at the southern tip of the reef from research at Heron Island near Gladstone, adding he hoped the boundary of the bleaching event would be found not too far below Townsville in coming days.

The bleaching has been caused by substantially warmer ocean temperatures than normal. In the northern waters of the Great Barrier Reef sea temperatures have been more than one degree higher than the long-term average in recent months.