The Great Barrier Reef has survived five climate-related "death events" over the last 30,000 years but may not be resilient enough to bounce back from the current decline, a scientific report said Tuesday.
The Reef, off Australia's eastern coast, is the world's largest coral system - larger than Italy - and one of most biodiverse ecosystems on the planet with millions of marine life forms.
In recent years, it has suffered an onslaught from a crown-of-thorns starfish epidemic, sedimentation, degradation of water quality, ocean acidification and massive back-to-back bleaching events in 2016-17 that scientists said "cooked" parts of the Reef.
The 10-year-long multinational study, published in Nature Geoscience journal on Tuesday, is the first of its kind to reconstruct the evolution of the reef over the past 30 millennia in response to major and abrupt environmental changes.
It said the Reef adapted to sudden changes in the environment in the past by moving across the sea floor as the oceans rose and fell.
The Reef is more resilient to major environmental changes such as sea-level rise and sea-temperature change than previously thought, the study found.
But it remains an open question as to whether its resilience will be enough for it to survive the current decline of coral reefs, said Jody Webster, the lead researcher and associate professor at the University of Sydney.
"I have grave concerns about the ability of the reef in its current form to survive the pace of change caused by the many current stresses and those projected into the near future," he said.
The study used data from fossil reef cores at 16 sites at Cairns and Mackay in Queensland, according to a statement from the university.
The study covers from the period before the "Last Glacial Maximum," 20,000 years ago, when sea levels were 118 meters below current levels, to the emergence of the modern reef some 9,000 years ago.
The Reef suffered five widespread death events but it was able to re-establish itself over time due to the continuity of reef habitats with corals and coralline-algae and the reef's ability to migrate laterally at between 0.2 and 1.5 meters a year, the study said.
But the reef is unlikely to survive current rates of sea surface temperature rises, sharp declines in coral coverage, year-on-year coral bleaching, decreases in water quality and increased sediment flux since European settlement, according to the scientists.
Previous studies have established a past sea surface temperature rise of a couple of degrees over a timescale of 10,000 years, but current forecasts change are around 0.7 degrees in a century, Webster said.
He also said the reef has been particularly sensitive to sediment fluxes in the past.
"That means, in the current period, we need to understand how practices from primary industry are affecting sediment input and water quality on the reef," he said.
It is a concern that environmentalists have been raising in recent years, as increased quantities of sediment, largely from grazing lands and due to deforestation, are entering the Reef affecting the water quality and reducing sunlight available to corals.
Scientists say it risks serious long-term effects on reef's health, as well as decreases its resilience to face other pressures like bleaching and ocean acidification.
The Reef is a top tourist attraction in Australia, generating some $6.4 billion a year and providing more than 64,000 jobs.
The Australian government announced earlier this month to spend $500 million ($380 million) to help restore and protect the Reef in the coming years, including improving water quality.
