Coral bleaching threat level raised on heritage-listed Great Barrier Reef

Severe coral bleaching is now taking place in some parts of Australia's Great Barrier Reef, as marine areas suffer the effects of the longest-ever global coral bleaching event on record.

The threat of coral bleaching on the reef has raised the authorities' response to its highest level, Australia's Minister for the Environment Greg Hunt announced at a press conference Sunday.

Hunt, who had just visited the world heritage-listed marine park to survey the damage, said the threat was now at "response level three" of the Great Barrier Reef Marine Park Authority's (GBRMPA) coral bleaching plan, indicating severe regional bleaching.

"What we are seeing is evidence there is clearly a coral bleaching event," he said. While Hunt suggested the bottom three quarters of the 344,400-square kilometre reef remained in a strong condition, the state of coral deteriorated as he headed north towards Queensland's Lizard Island.

Hunt said "patches of white or grey" coral became more prominent in the north of reef.

Coral bleaching occurs when coral expels the algae that lives in its tissue, giving it food and colour. This action, caused by stresses such as increased water temperature, leaves the coral skeleton exposed, making it more susceptible to disease and pollution.

A strong El Niño climate event, combined with the impact of global warming and other factors, has prompted unusually warm ocean temperatures and the world's third-ever global coral bleaching event, which began in 2014 and is expected to continue throughout 2016.

In a statement, the GBRMPA said reefs near the tip of Cape York in the north of the state were worst affected, with up to 50% coral mortality. At this point, the majority of the reef looks like it could be spared the worst of the global coral bleaching event due to improving weather conditions.

"Further wet weather has brought down ocean temperatures, providing reefs south of Cooktown with a much needed reprieve," GBRMPA Chairman Russell Reichelt said in the statement. "We now need to see if local weather conditions over the next few weeks are favourable enough to prevent further bleaching and to help these reefs recover from the minor to moderate bleaching that we're continuing to see south of Cooktown."

Hunt said the government would be contributing resources to increase coral bleaching monitoring, as well as support reef-wide initiatives to reduce the numbers of crown-of-thorns starfish that damage coral, and also to lessen the flow of damaging sediment and nitrogen runoff from local agriculture throughout the major river valleys and estuaries of the reef.

Hunt's office has been contacted for detail regarding the response plan.

While the risk to the reef was severe, Hunt said he had been advised by the GBRMPA it was not yet the worst bleaching incident the reef had ever experienced. "At this stage, 1998 and 2002 were more extensive and more extreme and with greater consequence," he explained. "This event is not, however, over... we can hope there is grey skies and rain."

Have something to add to this story? Share it in the comments.