The government agency responsible for the Great Barrier Reef has confirmed the natural landmark has suffered a third mass coral bleaching episode in five years, describing the damage as “very widespread”.
The Great Barrier Reef Marine Park Authority said the assessment was based on information from in-water and aerial observations, and built on the best available science and technology to understand current conditions.
Guardian Australia revealed on Wednesday that Prof Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, concluded the reef had experienced severe mass bleaching in the 2019-20 summer based on his findings from a nine-day aerial survey trip.
By Thursday Hughes had assessed more than 800 reefs, covering 344,000 sq km, with another 200 sq km at the southern end to go. He was joined on the trip by an observer from the marine park authority.
In a statement, the authority said the accumulation of heat, particularly through February, had caused bleaching across large areas of the reef. The severity of the damage varied widely, but some southern areas that had been spared during mass bleaching events in 2016 and 2017 had now experienced moderate or severe bleaching.
It noted there was positive news for the tourism industry: reefs they rely on in the northern and central parts, including near Cairns and Port Douglas, experienced only moderate bleaching, and most corals there should recover. Some pockets of the reef remain unaffected by bleaching.
The authority said it would have a better understanding of the extent and severity of the bleaching once surveys finished on Friday, with analysis to continue over coming weeks.
“Once the aerial surveys are complete we will be able to compare this event to those of 2016 and 2017,” the statement said.
It stressed bleached corals would not necessarily die. “On mildly or moderately bleached reefs there is a good chance most bleached corals will recover and survive this event,” it said. “Equally, on severely bleached reefs, there will be higher mortality of corals.”
Global heating caused by escalating atmospheric greenhouse gases is a major threat to the world’s coral reef ecosystems. The UN’s Intergovernmental Panel on Climate Change found the published evidence suggested a majority of tropical coral reefs would disappear even if heating was limited to 1.5C and would be “at very high risk” at 1.2C. The globe has warmed about 1C since the industrial revolution.
About half the reef’s shallow water corals bleached and died in 2016 and 2017.
The authority reiterated that climate change was the “single greatest challenge” facing the reef. “While the strongest possible global efforts to reduce emissions are essential, it is critically important we continue to deliver the work already being undertaken to enhance the resilience of the reef,” it said.
Environment groups said the mass bleaching underlined the need to move away from fossil fuels.
Australian Marine Conservation Society campaigner Shani Tager said the news was devastating for the reef, the species it supports and the communities that rely on its health. She said reef industries reeling from the impact of coronavirus needed short- and long-term support.
“When the restrictions from this pandemic lift we will need the beautiful places in this world like our reef more than ever to heal, reconnect with each other and the natural world,” she said. “That means we need a healthy reef and climate policies that will give it a fighting chance.”
Kate Smolski, from Greenpeace Australia, said future economic stimulus packages must include measures to cut greenhouse gas emissions. Gavan McFadzean, from the Australian Conservation Foundation, said: “With help, the tourism industry can recover after Covid-19, but only if there is a healthy Great Barrier Reef to visit once this crisis is over.”
Specific observations from the aerial surveys include:
Inshore and offshore reefs between Tully and Townsville were severely bleached.
Offshore areas in the northern section, including highly valued tourism reefs, were more moderately bleached.
Inner and mid-shelf reefs between Townsville and Mackay were mostly severely bleached, though some areas used by the tourism industry were only moderately bleached.
Bleaching of reefs in the Swains and Pompey groups, at the marine park’s far southeast, was highly variable, with some severe, some moderate and some with minor or no damage.