Reef in crisis: scientists despair as corals perish

Some have been reduced to tears after visiting familiar research sites and finding landmark corals lifeless and smothered in brown algae.

The death is so widespread in the shallow lagoons of Heron, One Tree and Lizard islands that it's palpable.

At One Tree Island Research Station, at the southern end of the reef, University of Sydney marine ecologist Dr John Turnbull can smell the decay.

It's sour and sulphurous, as stressed and dying corals release chemicals into the water.

Colleague Dr Stephanie Gardner describes taking sediment samples back to the lab, and finding them smelly and weirdly sticky.

"It looks wrong. It feels wrong," the microbial ecologist says.

"It was really hard to go out that first day. We did probably 10 snorkels and I broke down about three times. Seeing the corals like that, on their last legs, it's just horrifying."

Horrifying. Horrible. Depressing. Distressing. Even catastrophic.

They're words scientists reach for over and over again as they document the devastation caused by the marine heatwave that swept across the reef earlier this year, causing it's fifth mass bleaching event in eight years.

On Lizard Island, at the northern end of the reef, Dr Anne Hoggett seems angry at the frequency of hits her beloved island has endured, as the world keeps trading in the fossil fuels that drive marine heatwaves.

She recalls the devastation of 2016 when corals bleached en masse at Lizard, where the Australian Museum owns and operates a research station used by scientists from all over the world.

"They would have again in 2017 if there'd been any susceptible corals left to kill by then. But there wasn't."

There was a reprieve in 2018 and 2019 but since 2020 the island's reefs have bleached every single year.

"Right now we are seeing corals die, big time. Out on the reef flat, in the very shallow areas, we've lost at least 80 per cent of the Acropora corals. It's not all corals, but they are the dominant type in this area. So it's huge."

Dr Hoggett knows the reef can recover if it gets enough of a break between hits.

There was certainly good recovery after the devastation of 2016, but with five events in as many years she wonders: "Can corals continue to recover like that? I don't think so."

Back in more southerly waters, at Heron Island Research Station, marine ecologist Dr Stuart Kininmonth says the seascape was completely changed by the marine heatwave.

And it happened in a few short weeks, "almost like a wildfire" he says, with average water temperatures pushed to about 30C. Even deeper waters that should have been much cooler weren't.

"Some of the surveys I've done around Heron, it's pretty much close to 100 per cent of colonies are affected," the University of Queensland researcher says.

The result is a mix of dead corals and survivors that are trying to "claw their way back" now water temperatures have returned to average.

While there's some early evidence of some recovery, he's worried because winter is coming and the corals so recently ravaged by extreme heat may not have time to build the sugar reserves they need to make it through.

Terry Hughes is an emeritus professor at James Cook University who sits on an independent panel of reef experts that advises the government.

He's just returned from Heron Island and describes the damage there as catastrophic.

"Somewhere between 60 and 80 per cent of the corals on Heron, depending where you go, are already dead," he says.

As for the bleaching across the entire reef system, he says official maps show it's huge.

He is bothered by the disconnect between what "non-government scientists" from Heron, One Tree and Lizard islands are saying and the muted language coming from the Great Barrier Reef Marine Park Authority, which reports to federal Environment Minister Tanya Plibersek.

"It's certainly being undersold as a catastrophic event," says the respected professor, who's known for his frank commentary of reef management efforts.

He also says that's no surprise given the government is lobbying hard to keep the reef from being listed as a World Heritage site in danger.

The World Heritage Committee will consider the issue at a meeting in July and the government recently dispatched its special envoy for the reef, Senator Nita Green, and the CEO of the Great Barrier Reef Marine Park Authority, Josh Thomas, to Paris to meet with UNESCO.

The visit, in early April, was unannounced and details about exactly what was shared are scant. AAP has asked to interview Senator Green and Mr Thomas but those requests have not been granted.

In a brief statement, Senator Green said the meeting was to discuss "the ongoing health, protection and management of our precious World Heritage site" including the "significant progress Australia is making in implementing climate action, water quality improvements and fisheries reform".

Mr Thomas also provided a brief written response, saying the reef authority shared the latest information about the health of the reef, including the mass coral bleaching event declared by the authority on March 8.

He did not indicate what was said about its severity, nor did he answer questions about whether a preliminary assessment of coral deaths would be provided before the World Heritage Committee meeting in July.

The authority has previously warned a full assessment will take time, given not all bleached corals die. Some recover although can be at greater risk of disease, some die immediately, and others can die slowly over a period of months.

"In-water surveys have now been completed and we're compiling and analysing the data from numerous sources. Once this analysis is complete, we will be able to provide an assessment of mortality," Mr Thomas said.

AAP also asked the environment minister for details about the UNESCO meeting, including what was said about the severity of the bleaching.

A spokesperson told AAP the government was "continuing to engage constructively with UNESCO, the World Heritage Advisory Bodies and the World Heritage Committee" on the reef's long-term health.

The statement also pointed to Labor's emissions reduction and renewable energy targets, and its reef health investments, including projects to help aid bleaching recovery.

Australian Associated Press