Great Barrier Reef
Peter Gash, owner and manager of the Lady Elliot Island Eco Resort in the Great Barrier Reef area, snorkels during an inspection of the reef's condition in an area called the 'Coral Gardens' located at Lady Elliot Island, Australia, in this June 11, 2015 file photo.Reuters

Scientists confirmed a mass bleaching event on the Great Barrier Reef this year killed more corals than ever before, with more than two thirds destroyed across large swathes of the biodiverse site.

The 2,300-kilometre long reef -- the world's biggest coral ecosystem -- suffered its most severe bleaching in recorded history due to warming sea temperatures during March and April with the northern third bearing the brunt.

Follow-up underwater surveys, backing earlier aerial studies, have revealed a 700-kilometre stretch of reefs in the less-accessible, and more pristine, north lost 67 percent of their shallow-water corals in the past eight to nine months.

But further south over the vast central and southern regions, including major tourist areas around Cairns and the Whitsunday Islands, there was a much lower death toll.

"Most of the losses in 2016 have occurred in the northern, most-pristine part of the Great Barrier Reef," head of the Centre of Excellence for Coral Reef Studies at James Cook University Terry Hughes said.

"This region escaped with minor damage in two earlier bleaching events in 1998 and 2002, but this time around it has been badly affected."

Bleaching occurs when abnormal environmental conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae, draining them of their colour.

Scientists estimate the northern region, which teems with marine life, will take at least 10-15 years to regain lost corals, but are concerned that a fourth major bleaching event may occur before that, hampering the recovery.

Earlier this year, the reef studies centre warned that if greenhouse gases keep rising, similar events will be the new normal, occurring every two years by the mid-2030s.

Great Barrier Reef
ARC Centre of Excellence for Coral Reef Studies

According to an article in The Conversation, the reef science and management community will continue to gather data on the bleaching event as it slowly unfolds. The initial stage focused on mapping the footprint of the event, and now we are analysing how many bleached corals died or recovered over the past 8-9 months.

Over the coming months and for the next year or two we expect to see longer-term impacts on northern corals, including higher levels of disease, slower growth rates and lower rates of reproduction. The process of recovery in the north – the replacement of dead corals by new ones – will be slow, at least 10-15 years, as long as local conditions such as water quality remain conducive to recovery.

As global temperatures continue to climb, time will tell how much recovery in the north is possible before a fourth mass bleaching event occurs, David Wachenfeld, Director for Reef Recovery at the Great Barrier Reef Marine Park Authority, wrote in The Conversation.

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