A safety curtain of air bubbles has been installed in South Australia’s Spencer Gulf in an emergency bid to protect giant cuttlefish from the risk of a “near-extinction event” caused by the deadly algal bloom.

Each year, in a globally unique natural phenomenon, tens of thousands of giant Australian cuttlefish gather off the coast of Whyalla to breed.

But this year scientists fear for the cuttlefish population, with hatchlings due to emerge in late spring, given the toxic bloom is already present in the gulf and creeping northwards towards their breeding site at Point Lowly.

An experimental 200 metre by 100 metre “bubble curtain” funded by the state and federal governments was put in place this week and undergoing testing, with the aim of protecting about 50,000 to 80,000 cuttlefish eggs and hatchlings.

The technology uses land-based generators and compressors to pump air through underwater feeder lines and tubing, creating bubbles designed to disrupt the movement of algae and create a buffer zone along the rocky reef.

It has been successfully trialled in Western Australia to protect kelp from fish, but never been used in SA before, or at this scale.

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Dr Zoe Doubleday, a cuttlefish and octopus expert at the University of South Australia, says the aggregation of giant Australian cuttlefish, which takes place each year from late May to August, is globally unique.

“It’s the only population of giant Australian cuttlefish – and only population of cuttlefish worldwide – that comes together and breeds in their tens of thousands and forms this spectacular natural wonder,” she said.

Doubleday described the curtain as a “worst-case scenario measure” in the event the bloom reached the eggs or the hatchlings. “It’s in situ, so … they only need to switch it on if the algae starts approaching.”

After spawning, giant cuttlefish adults usually die as part of their lifecycle, leaving the next generation entirely dependent on the success of their eggs.

“Because mum and dad die, these eggs are essentially it,” Doubleday said. “If the bloom does reach them – and they take three to five months to incubate and hatch – they could have potentially a near-extinction event.”

The giant cuttlefish aggregation is a ‘spectacular natural wonder’. Photograph: Stefan Andrews/Great Southern Reef Foundation

She said the curtain was designed to protect a proportion of the cuttlefish eggs: enough for the population to bounce back in case others die due to the bloom.

Prof Gretta Pecl from the University of Tasmania’s Institute for Marine and Antarctic Studies, who is a member of the Biodiversity Council, said the Spencer Gulf trial was “important to test the effectiveness of this technique” in a future where more blooms were possible.

The most recent update on the state’s harmful algal bloom, released on Wednesday, indicated marine heatwave conditions, a contributing factor, had abated along the coast and in shallower waters. However, satellite images also showed elevated and increasing levels of chlorophyll, an indicator of algae concentrations, along the western coastline of the Spencer Gulf up to Murninnie Beach – about 90km from the Cuttlefish Coast Sanctuary Zone.

The latest giant cuttlefish counts estimated the population at about 63,400 this season, compared with 81,420 in 2024.

The statepremier, Peter Malinauskas, said the government was taking advice from its scientific advisory panel, which considered the curtain the best chance of protecting the species.

“The giant Australian cuttlefish is an iconic and spectacular creature,” he said. “The state government is doing everything it can to ensure this precious population survives the algal bloom.”