Toxic Algal Bloom Devastates South Australia’s Coast

 

A devastating ecological crisis is unfolding along South Australia’s coastline, where a massive toxic algal bloom has transformed vibrant marine ecosystems into underwater graveyards.

Since March, the harmful bloom — fueled by a marine heatwave — has spread across more than 4,500 square kilometers (1,737 square miles) of coastal waters, killing an estimated 15,000 animals from over 450 species. The algae have poisoned iconic native creatures such as longfinned worm eels, leafy seadragons, surf crabs, and even common bottlenose dolphins.

Ecologist Professor Scott Bennett described seeing the sea floor littered with the lifeless remains of razor clams during a recent trip to the Great Southern Reef. “100% of them were dead and wasting away,” he said.

A report from the Biodiversity Council, backed by 11 Australian universities, calls it “one of the worst marine disasters in living memory.”

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A Crisis Set in Motion by Climate Extremes

The event traces its origins to a chain reaction of climate-related factors. In 2022, catastrophic flooding along the Murray River pushed nutrient-rich runoff into the Southern Ocean. This was followed by cold water upwelling that brought more nutrients to the surface. Then came the heat: by September 2024, ocean temperatures had risen 2.5°C above average — a perfect storm of conditions for algal growth.

The species responsible is Karenia mikimotoi, a planktonic algae that doesn’t pose lasting harm to humans but can suffocate fish and invertebrates by damaging their gills. The bloom, which began off Gulf St Vincent, quickly spread — reaching Kangaroo Island in May, and Adelaide’s beaches by July.

The algae also forms yellow foam and releases toxins that likely caused health symptoms reported by surfers earlier in the year: sore throats, coughing, and blurred vision.

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Widespread Ecological and Economic Fallout

Beyond the environmental toll, the bloom has delivered a crushing blow to South Australia’s fishing industry. Commercial squid fisher Nathan Eatts hasn’t caught anything since April. “On a good day, I could catch 100 squid. Now — nothing,” said Eatts, whose family has fished the Fleurieu Peninsula for generations.

“Wherever the algal bloom hits, there is zero life,” said Pat Tripodi, head of the Marine Fishers Association. About a third of the state's waters are now biologically barren, leaving seafood processors, grocers, transport companies, and restaurants reeling from the loss.

The industry, valued at nearly A$480 million ($315 million USD), is facing an uncertain future. “It’s an enormous emotional and mental strain,” Tripodi added.

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Nature’s Warning Sign

Toxic algal blooms are not new — they occur worldwide, including in the U.S. — but scientists warn that climate change is making them more frequent and more severe.

Bennett, a marine scientist at the University of Tasmania, emphasized that this event should not be dismissed as an isolated anomaly. “This is symptomatic of climate-driven impacts that we’re seeing across Australia,” he said.

About 70% of species on the Great Southern Reef are endemic — found nowhere else on Earth. “For these species, once they’re gone, they’re gone,” Bennett warned.

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A Disaster Without a Playbook

Unlike bushfires or floods, there’s no direct way to stop a harmful algal bloom. Its course is dictated by weather and ocean conditions, making it almost impossible to predict or control.

“This is a natural disaster — but unlike ones we’re used to,” said South Australian Premier Peter Malinauskas. “With a bushfire, you can put the fire out. With this, we don’t know how it’s going to play out.”

This week, the federal and state governments jointly pledged A$28 million ($18.4 million USD) for cleanup and support. However, the federal government has not yet declared it a formal natural disaster, which would unlock additional resources and aid.

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Looking Ahead: What Can Be Done?

Bennett says the only long-term solution lies in climate action. Reducing carbon emissions, restoring marine habitats, and protecting natural filters like kelp forests and seagrass beds are critical.

“Marine ecosystems can be resilient,” he said. “But only if we act now to protect them.”

For people like Eatts, the devastation is deeply personal. “You take for granted where you live and what you see every day,” he said. “But one event like this can break your heart.”

As the algae continue to spread and the death toll mounts, the message from scientists and fishers alike is clear: this is not just a wake-up call — it’s a warning siren.