Wildlife

Coral bleaching at Barrier Reef: 'severe'

Australian authorities said Sunday coral bleaching occurring in the World Heritage-listed Great Barrier Reef had become "severe", the highest alert level, as sea temperatures warm.

Australian Environment Minister Greg Hunt said while the bleaching at this stage was not as severe as in 1998 and 2002, also El Nino-related events, "it is however, in the northern parts a cause for concern".

"The reef is 2,300 kilometres (1,429 miles) long and the bottom three-quarters is in strong condition, but as we head north, it becomes increasingly prone to bleaching," Hunt said after an aerial tour of some of the affected areas Sunday, the Australian Broadcasting Corporation reported.

"Essentially what you could see was patches of coral bleaching as you approached Lizard Island (located in the Barrier Reef)."

The reef -- the world's biggest coral reef ecosystem -- is already struggling from the threat of climate change, as well as farming run-off, development and the coral-eating crown-of-thorns starfish.