The ‘underwater bushfire’ coming for Australia that can’t be stopped

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A severe marine heatwave is bearing down on southern Australia, threatening fisheries, tourism and biodiversity along a vast tract of coast that hosts 67 per cent of the nation’s population.

The approaching heatwave is like an “underwater bushfire that can’t be extinguished”, according to a group of experts concerned about the fate of the 8000-kilometre Great Southern Reef.

Scientists survey Lonsdale Reef, near Geelong, one of the biodiverse havens that make up the 8000-kilometre Great Southern Reef.Credit: Antonio Cooper, courtesy Great Southern Reef Foundation

The marine and climate scientists from the Great Southern Reef research partnership have asked Environment Minister Tanya Plibersek and Climate Change Minister Chris Bowen for $40 million over 10 years to help monitor and safeguard the reef.

“The Great Southern Reef borders onto 63 federal electorates, is more economically valuable than the Great Barrier Reef, and yet receives less than 1 per cent of the funding,” the researchers wrote.

“Estimates predict a 20 per cent decline in habitat on the Great Southern Reef will lead to a $30 billion loss to the Australian economy over the next two decades.”

Where is the Great Southern Reef?

As the Great Barrier Reef consists of 2000 vibrant tropical coral reefs, the Great Southern Reef is a system of interconnected temperate reefs stretching from Kalbarri in Western Australia to the NSW-Queensland Border.

“In shallow waters, it’s dominated by kelp forests and seaweed communities. They’re rocky reef habitats,” Dr Scott Bennett, a marine ecologist at the University of Tasmania and signatory to the letter, said. “As we get into deeper environments it turns into these beautiful sponge and soft coral gardens.”

Characterised by golden and giant kelp (which can grow half a metre per day), giant cuttlefish, sea lions, abalone, blue swimmer crabs and weedy seadragons, the reef has more unique species than its northern world heritage-listed counterpart.

“Seventy per cent of species are endemic, unique to the region, not found anywhere else,” Bennett said. “On the Great Barrier Reef about 3 per cent of species are endemic. What we have here is hugely unique.”

But the species of the Great Southern Reef have evolved over 50 million years to suit a narrow, normally stable temperature range. With an “off-the-charts” heatwave bearing down, Bennett and other scientists are concerned parts of the reef’s lush underwater kelp forests could be razed.

Bennett said efforts to monitor changes to the reef – which provides 20,000 tonnes of seafood per year and $11.5 billion worth of ecosystem services, including carbon uptake – are critically underfunded.

“We are running absolutely blind as to how the species are responding to change,” Bennett said.

“The government is funding species recovery plans and there’s a lot of emphasis on regeneration, recovery, restoring ecosystems. But unless we know how they’re changing in the first place, we have no capacity to respond.”

A blue groper at Shelly Beach, Manly, a snorkelling hotspot on the Great Southern Reef.Credit: Gergo Rugli, courtesy Great Southern Reef Foundation

What are the effects of an intense marine heatwave?

Plibersek said she shared the concern of scientists and that the government would consider the letter alongside the recommendations of the senate inquiry into the reef which is due to be handed down next week.

In 2011, a marine heatwave destroyed a 100-kilometre stretch of kelp off the coast of WA. The 4 to 5 degree temperature spike shuttered crab and scallop fisheries, ushered tropical species into Perth’s Swan River and drove little penguin breeding success to its lowest in 20 years.

The urgent goal ahead of the next severe heatwave is to be better prepared, said algal expert Professor Adriana Verges.

Snorkelers may notice dead patches of golden kelp, a defining species of the Great Southern Reef destroyed by marine heatwaves.Credit: Professor Adriana Verges

“The GSR provides a whole lot of benefits to us humans. The most obvious and economically valuable are fisheries – abalone and rock lobster are very valuable to Australia. It’s not just an ecological issue, it cascades onto the economy,” Verges, from UNSW, said.

A continent-spanning band of golden kelp, a common seaweed for Sydney and Melbourne beachgoers, makes up the backbone of the Great Southern Reef. But it’s vulnerable to heat stress and bleaching due to disease exacerbated by warmer water, Verges said.

When will the heatwave hit?

The heatwave will peak between December and February, and the most intense anomalies will flare off the coast of Tasmania, according to the Bureau of Meteorology.

The bureau’s oceanographer Grant Smith told AAP the heat could climb 2.5 degrees above the average, surpassing the highest temperature level on the forecasting scale.

Golden kelp makes up the backbone of the reef, providing habitat and carbon sequestering services along 8000 kilometres of coastline. It’s vulnerable to spikes in heat.Credit: Louise Nott, courtesy Great Southern Reef Foundation

“We didn’t account for anomalies that high when we developed this … it could be 3C, it could be 3.5C, but we can’t see how high it goes,” Smith said.

Ocean temperatures around Australia have warmed 1.1 degrees since 1900 – which may not seem like much, but given that underwater is a fairly stable environment, small changes can be dramatic. 

Generally, eastern waters have warmed faster than those to the west, with the Tasman Sea one of the fastest warming areas. Marine heatwaves have doubled in frequency and are becoming more intense due to human-caused climate change, according to the IPCC.

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