Higher water temperatures this year have caused the worst erosion of corals ever recorded on Australia's Great Barrier Reef.
Scientists estimate two-thirds of coral coverage has died along a 700km stretch of reef off far north Queensland, north of Port Douglas.
Staghorn corals killed by coral bleaching on Bourke Reef, on the northern Great Barrier Reef, November 2016 Photo: Greg Torda / ARC Centre of Excellence for Coral Reef Studies.
Coral bleaching happens when water temperatures rise for a sustained period of time.
In February, March and April, sea surface temperatures across the Great Barrier Reef were the hottest on record, at least 1°C higher than the monthly average.
Queensland scientists have confirmed that resulted in the largest die-off of corals ever recorded on the Reef - though some areas showed remarkable improvement.
James Cook University researchers have been carrying out underwater surveys since the severe coral bleaching event.
"When bleaching occurs, in the 6-12-month period afterwards, the corals either survive and regain their colour, or if they don't regain their colour, they slowly die," said JCU professor Terry Hughes.
Prof Hughes described the northern area as severely damaged and estimated it could take between 10 and 15 years for new corals to grow.
"The bleaching in the northern section was so severe that corals that don't normally bleach, have.
"And so when you lose a 50-year-old coral, you can't [fix] it in just a handful of years."
Researcher Grace Frank carrying out a bleaching survey on One Tree Reef on the southern Great Barrier Reef. Photo: Tory Chase / ARC Centre of Excellence for Coral Reef Studies.
While the northern reef struggled, there was good news for southern parts of the reef, which includes major tourist areas around Cairns and the Whitsundays.
Surveys of areas south of Port Douglas showed a remarkable improvement in coral health and recovery.
The big issue for JCU researcher Andrew Baird was when the next bleaching would occur.
"Those reefs around Townsville and further south didn't bleach this year, hopefully they're not going to bleach next year.
"But who knows when the next major bleaching event will happen?"
- ABC / BBC