Following a major long-term study scientists have revealed Australia’s Great Barrier Reef suffered a “catastrophic die-off” of coral during an extended heatwave in 2016, threatening a broader range of reef life than previously feared.

The underwater heatwave that bleached massive sections of the reef in 2016 was so severe it immediately “cooked” some corals in the northern region.

The French newsagency AFP reports the scientists said some 30 per cent of the reef’s coral died in the heatwave from March to November 2016, the first of an unprecedented two successive years of coral bleaching along the 2300-kilometre World Heritage-listed reef off Australia’s north-eastern coast.

The study, published today in the journal Nature, found the coral, which serve as habitats for other creatures, were particularly hard hit by the rising sea temperatures caused by global warming.

Professor Terry Hughes, a report co-author and head of the Centre of Excellence for Coral Reef Studies at Australia’s James Cook University, told AFP the most susceptible to heat exposure were branching corals, table-shaped creatures that provide nooks and crannies for fish nurseries and fisheries.

Corals that were more likely to survive the warmer sea temperatures were smooth and melon-shaped, he said.

“While they were good calcifiers that add volume to reefs, they were “not very useful as habitable providers”.

“So there is a shift in the mix of species and the overall loss of corals has a broader impact on all the creatures that depend on the corals for food and habitats,” Professor Hughes said.

The findings come as a scientific advisory body to the United Nations considers what parts of the natural world are on the verge of an environmental failure.

The JCU researchers said their work showed climate change was threatening the Great Barrier Reef with ecological collapse.

The research centre said the new study showed that corals on the northern Great Barrier Reef “experienced a catastrophic die-off” following the 2016 heatwave.

“The coral die-off has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining,” said Professor Andrew Baird, another of the report’s authors.

The scientists said the focus should be on protecting the surviving corals, which number about a billion after the two bleaching events in 2016 and 2017.

“They are the ones that are going to re-feed and repopulate an altered reef into the future,” Professor Hughes said, adding that one way to maintain their health was through improving water quality by reducing coastal pollution.

They concluded the 2016 bleaching event was the beginning of a long-term transformation, which has altered the Great Barrier Reef “forever”.

Efforts to curb climate change, such as through the United Nations sponsored Paris Agreement to cap global warming at under 2.0 degrees Celsius below pre-industrial levels, were also critical.

“We’ve now seen four bleaching events (1998, 2002, 2016 and 2017) on the Great Barrier Reef with one degree (Celsius) of global average warming,” he said.

“We are on a pathway where we are committed to a different Barrier Reef. If we continue with business-as-usual emissions, then I don’t think the reef can survive.”

Coral reefs make up less than one per cent of Earth’s marine environment, but are home to an estimated 25 per cent of ocean life, acting as nurseries for many species of fish.

The Australian government’s Great Barrier Reef Marine Park Authority concluded the bleaching in 2016 was caused by a record-breaking marine heatwave, caused by a combination of climate change and the El Nino weather cycle.

Dr Sarah Perkins-Kirkpatrick from the Climate Change Research Centre at the University of New South Wales recently published work showing underwater heatwaves have increased in both their duration and frequency over the past century, with a sudden uptick since the 1980s.

As a result, on average around the globe, there are 54 per cent more days each year that are subject to a marine heatwave.

“The sorts of events that cause coral bleaching will occur more often in the future,” Dr Perkins-Kirkpatrick said.

She added she was shocked by the results of Professor Hughes’s paper.

“I’ve got to say, it’s catastrophic. Seeing all the news articles and seeing it evolve, it looked catastrophic,” she said.