A pair of giant Australian cuttlefish at Point Lowly, South Australia (Photo: Philip Garner/Shutterstock)

The Australian government is investing AU$700,000 to install a ‘bubble curtain’ which will protect South Australia’s giant cuttlefish from a toxic algal bloom.

Between May and August each year, hundreds of thousands of giant Australian cuttlefish (Sepia apama) migrate to the South Australian coastline near Whyalla to mate.

This year, however, the breeding grounds are under threat from a toxic algal bloom that has been growing in size since March.

The bloom, made up of the species Karenia mikimotoi, is a natural phenomenon but one that scientists from the South Australian Research and Development Institute (SARDI) say has been exacerbated by the marine heatwave of 2024 – although this has reportedly now abated.

A similar bloom occurred in South Australia’s Coffin Bay in 2014, and lasted four months before dissipating.

While many algal blooms are harmless, this one is proving extremely toxic to some marine fauna. It is known to affect the gills of fish, and dead cuttlefish have been washed up on beaches close to the phenomenon.

Scientists have considered collecting eggs from the cuttlefish and relocating them to a different area, but this comes with several concerns.

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Algae blooming on Semaphore Beach, Adelaide, South Australia (Photo: Sigorvision/Shutterstock)

The population of giant Australian cuttlefish is regarded as relatively healthy (the IUCN Red List labels them as ‘Near Threatened’), and they return to the same area every year to breed – a site preference that is not well understood.

Taking the eggs elsewhere might expose them to predators not present at the Whyalla breeding site, and may not, in fact, protect them from the effects of the algal bloom, the movements of which are difficult to predict.

The 200 by 100-metre bubble curtain will be installed on the Eyre Peninsula of the aptly named Cuttlefish Coast, with the aim of preventing, or seriously reducing, the amount of algae that is able to pass through the bubbles.

The curtain will be created by deploying tubes along the rocky reef, which ranges in depth from two to seven metres, that will be fed by land-based compressors.

Deputy South Australia Premier Susan Close said the bubble curtain was ‘a trial’ and may not be necessary if the algal bloom changes course.

‘It hasn’t been done like this for this particular species before. But we have every reason to think that where we install it we will hold the algae back,’ said Ms Close in a press conference detailing the strategies being discussed to preserve the cuttlefish.

‘Because this population is so important to South Australia, we think it’s worth that investment,’ she continued. ‘We’ll be paying very careful attention obviously to the movement of the algae up the coastline. 

‘If the algae doesn’t make it up we won’t need to turn it on.’

The bubble curtains have been used before, but not at such a scale.

‘It’s usually been used around things like aquaculture pens, so deploying it at a large scale is something relatively new,’ said Australia’s Biodiveristy Council CEO James Trezise.

‘Hopefully there’ll be a lot of learning and insights that arise out of this.’

A giant Australian cuttlefish shot at Whyalla, South Australia (Photo: Philip Garner/Shutterstock)

Whyalla Dive Shop owner and director of the Eyrelab not-for-profit conservation organisation, Manny Katz told ABC News that protecting the cuttlefish ‘would benefit both the environment and the community’.

‘From a business point of view it’s great because so many Whyalla-based businesses benefit from the cuttlefish industry … from the tourism aspect,’ said Katz.

‘The amount of divers and snorkellers coming up from Adelaide who want to interact with a marine ecosystem that is healthy … [has] been a saving grace for a lot of ocean enthusiasts, seeing a place that’s not totally destroyed.

‘We need to monitor and hopefully restore impacted sites around SA, but we also have to protect sites from getting impacted as well.’