This year, the middle third of the reef has experienced particularly intense bleaching.
An aerial survey conducted by the scientist with the Australian Research Council's Centre of Excellence for Coral Reef Studies assessed 800 coral reefs across 8,000km.
Two-thirds of Australia's iconic Great Barrier Reef has been damaged by back-to-back severe bleaching events caused by record-breaking temperatures, scientists warned today, adding the reefs affected a year ago have zero prospect of recovery.
Great Barrier Reef coral bleaching composite map shows surveyed coral reefs in 2016 (left panel) and 2017 (right panel).
Researchers have declared that this year coral bleaching event has severely affected the central part of the reef.
The recent impact of tropical cyclone Debbie, which struck north-eastern Australia at the end of March, is believed to have damaged the reef for an about 100-km-wide strip along its path.
Hughes said that the reef was struggling with multiple impacts.
"By all accounts the cyclone has caused tremendous damage to the reefs in the Whitsundays", Steinberg said.More news: Sergio Garcia wins Masters after one-hole playoff with Justin Rose
Australia's Great Barrier Reef has been hit by severe coral "bleaching" for the second year in a row in the face of record-breaking temperatures, scientists have said.
"There is a rapidly closing window where we still have the opportunity to address this issue". Before 2016, only two bleaching events occurred in two decades-and yes, global warming has been linked directly to it.
Great Barrier Reef Marine Park Authority chairman Russell Reichelt said survey results would be used to "refine a support strategy" to help improve the health of the ecosystem.
When surrounded by warmer-than-normal waters, corals expel tiny photosynthetic algae, draining them of their colour. After three years straight of record bleaching events, the news broke that some 65% of the coral of the northern reef is dead, and the coming months were expected to be even worse.
Coral are the oceanic canary in the coal mine and rising ocean temperatures are leaving them gasping for breath.
There have been four bleaching events over the past 25 years during 1998, 2002, 2016 and 2017.
Jon Brodie, a water quality expert who has devoted much of his life to improving water quality on the reef, said the reef was now in a "terminal stage".
A supplied image of bleaching damage on the Great Barrier Reef. "Going over those reefs this year, you can tell how low the coral cover was". Kerry said bleached corals don't always die, but take at least a decade to make a full recovery, so with back-to-back bleaching they expect coral loss.