South Australia’s algal bloom may shrink over winter – but this model suggests it will spread to new areas in summer

South Australia is desperate for help to tackle an unprecedented harmful algal bloom that has decimated marine life up and down the coast. While the extent of the damage is still unknown, my preliminary research suggests there’s no end in sight. It may just get better over winter before it gets worse next summer.

The Karenia mikimotoi bloom first appeared in March on two surf beaches outside Gulf St Vincent, about an hour south of Adelaide. It has since spread, killing all kinds of marine organisms – from crabs and small fish to sharks and rays. Only the neighbouring Spencer Gulf, far west coast and southeast coasts have been spared. For now.

In preliminary research now undergoing peer review, I have predicted the bloom’s future spread using a new computer model. In the worst-case scenario, the harmful algal bloom would reach the Spencer Gulf and spread – from Port Lincoln to Whyalla and across to Port Pirie – next summer and autumn. That would be extremely bad news for the thriving seafood, aquaculture and tourism industries. They may need help to prepare.

Some help is on the way. Federal Environment Minister Murray Watt yesterday announced A$14 million in federal funding. SA Premier Peter Malinauskas convened an Emergency Management Cabinet Committee meeting today and signed off on a $28 million support package.

A rolling disaster

The algal bloom was first noticed when dozens of surfers and beachgoers on the southern coast of the Fleurieu Peninsula fell ill after exposure to seawater in March.

Soon, dangerous sea foam appeared. Then the killing began in earnest. Many marine species started washing up dead or dying.

The bloom began to spread. In mid-April, K. mikimotoi was detected in water samples from Edithburgh and Coobowie on the southeastern corner of Yorke Peninsula.

In early May, the Kangaroo Island Council announced the bloom had spread across the Investigator Strait affecting the island’s northern coastline.

Wild weather in June pushed the bloom through the Murray Mouth into the Coorong.

By July, the state government had detected K. mikimotoi along Adelaide’s metropolitan coastline. Videos of fish kills near the Ardrossan Jetty in the northern Gulf St Vincent also emerged.

So far, the bloom has not been detected in Spencer Gulf. But my modelling suggests it’s only a matter of time.

Predicting the future

I was the first to discover the seasonal upwelling of nutrients in several regions along SA’s southern coastal shelf. This nutrient source fuels the marine food chain. It’s a big part of the reason why the marine life in our Great Southern Australian Coastal Upwelling System is so diverse.

I also simulated the ocean currents in South Australian gulfs using computer models as early as 2009.

I have now developed a computer model to predict where the algae will spread next.

Preliminary results from this research have been submitted to the journal Continental Shelf Research and are being reviewed. But given the speed at which this situation is developing, it’s worth sharing a preprint of this manuscript.

My model matches what’s known about the early spread of the bloom. It began in the coastal waters of the southern Fleurieu Peninsula. It then invaded Investigator Strait, between the Yorke Peninsula and Kangaroo Island, before slowly spreading in a clockwise circulation across the wider Gulf St Vincent.