The underwater cyclone that could hit Australia’s east coast

The harmful algal bloom devastating marine ecosystems off the coast of South Australia is the largest of its kind ever recorded in Australia and could easily occur on the east coast, experts warn.

On Tuesday, the South Australian government announced it will match funding promised by the federal government, bringing the total package to deal with the deadly Karenia mikimotoi outbreak to $28 million.

Dead garfish in neon-green water in Ardrossan, South Australia on July 9.Credit: Stefan Andrews / Great Southern Reef Foundation

The outbreak of the toxic microalgae was first discovered in March on the Fleurieu Peninsula, and has since spread to the Yorke Peninsula, Kangaroo Island, Gulf Saint Vincent and Spencer Gulf.

Beachgoers and scientists have documented a vast array of sea creatures washing up dead on beaches. An online citizen science project has identified 450 species killed by the bloom, with the most affected being Southern Fiddler rays.

“It’s the biggest bloom of Karenia mikimotoi we’ve experienced in Australia, but [not] anywhere in the world,” said Professor Shauna Murray, a marine biologist at the University of Technology Sydney.

“There have been larger blooms of Karenia mikimotoi in northern China – it’s been very problematic there.”

A dead Port Jackson shark on Glenelg Beach.Credit: Getty

What caused the toxic algal bloom in South Australia?

SA Premier Peter Malinauskas said three factors had contributed to the deadly outbreak. The 2022-23 Murray River floods, the biggest since 1956, forced the largest volume of nutrients from the Murray-Darling system into the marine environment for 70 years.

Second, during the following summer, a longer-than-ever Bonney Upwelling – the natural phenomenon in South Australia that brings up nutrient-rich water from deep water to the surface – was recorded.

Finally, the ongoing marine heatwave means the waters around South Australia have been 2.5 degrees hotter than usual since last year.

“That allowed the algae, that was always there, to explode in its volume,” Malinauskus told reporters on Tuesday.

“It is reasonable to assume that we will see other events of this nature elsewhere in the country and other parts of the world.”

Could it happen on Sydney or Melbourne coastlines?

Murray said this was not only possible but “quite likely”, given it has already happened in the eastern states on a smaller scale.

Murray said there had been previous outbreaks of Karenia mikimotoi and other algae deadly to marine life in NSW and Victoria.

Harmful algal blooms that affected fishing and aquaculture by making fish unsafe to eat, rather than killing them, were also common.

“In terms of water column conditions and how similar it would be on the [east] coast, we have upwelling events ... we’ve had marine heatwaves, we’ve had all of those things,” Murray said.

Can anything be done to fix the algal bloom?

The SA government has said “nothing can be done naturally to dilute or dissipate the bloom”.

Murray said Korea and Japan had decades of experience dealing with harmful algal blooms affecting aquaculture facilities, and had researched several strategies, including sprinkling clay into the water to sink the algae.

But this had not been studied in the Australian environment. “We simply don’t have any data to back up whether any of those methods would work, and most importantly, whether or not they would actually cause additional damage to the marine environment,” she said.

How is it harmful to marine life?

Karenia mikimotoi has choked ecosystems of oxygen, killing everything from bivalves, worms and cuttlefish to sharks, rays and dolphins.

“It’s similar in effect to a cyclone underwater,” Murray said.

Marine scientist Janine Baker from the Great Southern Reef Foundation said there would be long-term and widespread environmental, social and economic impacts.

“It’s dreadful – I’ve never seen anything like this in the 35 years I’ve been working in the marine environment,” Baker said.

“What concerns me is that because there are so many vacant niches now, it will promote the settlement of opportunistic and potentially invasive species.”

She said there were already introduced species from overseas and eastern Australia – such as long-spined sea urchins – and the problem was increasing with warming southern oceans.

Why won’t the federal government declare it a national disaster?

Federal Environment and Water Minister Murray Watt has said the Commonwealth Natural Disaster Framework was designed for events such as bushfires and cyclones, and the algal bloom did not fit the bill.

He argued the point of declaring a natural disaster was to unlock funding, and this was moot because he obtained $14 million in federal assistance anyway.

Federal Environment and Water Minister Murray Watt at West Beach in Adelaide on Monday.Credit: AAPIMAGE

Dr Scott Bennett from University of Tasmania’s Institute for Marine and Antarctic Studies said the government should treat the bloom as a natural disaster.

“The federal government needs to not treat this as an isolated event or a localised event – this is symptomatic of a broader national issue,” Bennett said. “We’re seeing more intense and more frequent marine heatwaves occurring around the country.”

What scientific research needs to happen?

The SA government said the $28 million package will include beach clean-up, assistance for affected businesses, and $13.5 million earmarked for science and monitoring.

That includes $8.5 million for a coastal monitoring network, $3 million for rapid assessment of fish stocks using remote underwater video surveys and dive surveys, and $2 million for a new national testing laboratory in South Australia for harmful algal bloom and brevetoxin/biotoxin testing. (At present, samples are sent to New Zealand for analysis.)

The catastrophe is affecting the Great Southern Reef, a rocky reef rich in biodiversity that extends from NSW, around the southern side of the continent and up the coast of Western Australia.

Bennett and other research partners in the Great Southern Reef Foundation have called for $40 million over 10 years for baseline research into the reef.

However, Bennett acknowledged the research focus needed to be on South Australia right now, first diagnosing the extent of the problem and then focusing on key habitat recovery.

Fortunately, the state already had experience restoring kelp forests, seagrass meadows and oyster reefs damaged by run-off, he said. “They’ve got a really strong track record in large-scale habitat restoration.”

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