Parts of the world's most southerly coral reef are under threat after it suffered its largest-recorded bleaching event.
Lord Howe Island is well known for its pristine environment and natural beauty.
Its isolation has allowed it to develop unique and endemic marine life and the waters contain an unusual mix of tropical, sub-tropical and temperate corals.
But since January the waters around Lord Howe have experienced unusually warmer temperature, 2°C above average, and the corals are showing the first signs of extensive bleaching.
Unlike the Great Barrier Reef, where corals have been known to recover, researchers are concerned the genetically unique reef at Lord Howe could take decades to regenerate.
Professor Peter Harrison of Southern Cross University in Lismore, New South Wales, says it is the most significant bleaching event ever recorded at Lord Howe Island.
"The significance of this is that Lord Howe Island has the southern-most coral reef, so when that starts to see signs of extensive coral bleaching we know that the climate is definitely changing," he says.
Harrison and a team of scientists have spent the past week diving off Lord Howe Island, assessing the extent of the stress.
In 1998, the reef survived relatively unscathed despite widespread coral bleaching around the world.
This year, not only have the ocean temperatures been higher, but conditions have been unusually calm, and that has contributed to the significance of the bleaching.
The island's marine park manager, Ian Kerr, says the still conditions meant water was not flushed out of the lagoon.
"So the lagoon especially had higher temperatures than it normally does and higher UV light," he says.
It is not known how much of the reef will recover.
Harrison says some mortality is expected, but cooler temperatures over coming months may reduce the stress.
"At the moment we really can't determine whether or not there [will] be serious mortality of corals at some of these sites or not," he says.
"It was personally very upsetting to go back to this absolutely gorgeous reef environment.
"It should be noted that at the moment it is still a beautiful pristine reef environment, but to go back and see so many of these corals bleached was really upsetting to me personally.
"I am hoping that the cooler sea temperatures will allow a decrease in stress and most of these corals come back really quickly and recover fully.
"But at the moment it is on a knife edge."