'Never had a situation like this': Why Australia is unprepared for this deadly ocean threat

SBS Australia

24-05-2025

Across South Australia's coast, toxic algae have been destroying marine life. Source: Getty, SBS, Supplied Edithburgh Jetty on South Australia's Yorke Peninsula is usually a hot spot for divers. Known for its azure blue waters and vibrant micro-ecosystem, dive enthusiasts come from all over the world to marvel at its marine wonders: leafy sea dragons, pyjama squid, rodless angler fish and vivid corals and sponges that cover the jetty's pylons. But since mid-March, life under the jetty has been decimated by a deadly algae bloom , now spanning four-and-a-half thousand square kilometres of South Australia's gulf and coastal waters. Cinematographer Paul Macdonald has been studying life under the jetty for more than 20 years and says the damage is staggering.
"It's been part of my life for so long, and now, to see this devastation, it's just heartbreaking," he says. "Words cannot describe how sad it is." Macdonald also runs a local dive school at the jetty with his wife, Elizabeth Solich. Their monitoring in recent years led to the Edithburgh rodless angler fish being confirmed as a new species in 2021 and given the Indigenous name Narungga Frogfish. "I'd seen it breed three times. It was always in the one spot, and the coral it was living in was the size of a football," Macdonald says.
To realise it was gone was a really sad moment. The harmful algae bloom (HAB) was initially identified as karenia mikimotoi, a phytoplankton that produces a reactive oxygen species that damages gills — preventing marine creatures from breathing.
It also causes respiratory and flu-like symptoms in humans. Another strain of karenia that produces small amounts of neurotoxin (brevetoxin) has also been identified in the bloom. What's perhaps most alarming is that little can be done to prevent HABs from occurring, but the effects can be mitigated with close monitoring.
Most of what is known about the impact of the bloom on marine species has come from data collected by citizen scientists like Macdonald and Solich. Karenia mikimotoi was first identified after surfers reported a mysterious foam at Waitpinga Beach on South Australia's Fleurieu Peninsula in March. Since then, more than 1,400 citizen reports and photos of dead or sick marine life have exposed the consequences of the HAB.
A shared database published on the inaturalist.org website shows that more than 200 different species of marine life have been killed. OzFish, one of the non-government organisations leading the project, identified more than 100 species of fish and sharks alone. "This includes rarely encountered deepwater sharks and iconic leafy sea dragons, and popular recreational fishing species like flathead, squid, and blue swimmer crabs, and rock lobsters," says OzFish's South Australian project manager Brad Martin.
There have been calls for increased monitoring and testing during HABs and questions raised over Australia's preparedness for future events. Faith Coleman, an estuarine ecologist, who has spent hours volunteering to educate the local community about the bloom, suggests the lack of data is "a wasted opportunity". Coleman runs an environmental consultancy agency with her mother, scientist Peri Coleman, and says the main response to the bloom has come from citizen action.
The Colemans have been undertaking plankton counts under a light microscope from samples collected by the citizen scientists. "That's really the only data we have in the public sphere," Coleman says.
So that means there is very limited stuff we can do, to work out how to stop it in the future. She says regular monitoring of swimming beaches and samples taken at sea and at depth are needed to study the bloom.
In the US, federal legislation governs the research and monitoring of HABs. Director of the Southern California Conservation Observing System, Clarissa Anderson, says this has led to "state-of-the-art monitoring systems" in areas with a history of HABs. "We've been lucky to have a big academic and now government investment monitoring program that goes back to the early 2000s," she says. "So we do have some pretty long-term records with which to put any one of these individual events into context." In Australia, the only labs testing for HABs at the species level are those paid for by the aquaculture industry.
Marine biologist Shauna Murray — who identified the first sample of karenia mikimotoi at Sydney's University of Technology — says there are only a handful of experts equipped to do this work in Australia. "I think largely there hasn't been that many samples collected, and that's largely because we don't have the infrastructure for it," Murray says. "We've never had a situation like this in the past where we've had to collect a lot of samples rapidly from a harmful algal bloom that's not just affecting the aquaculture industry, but is affecting the wider population." What's causing harmful algae blooms? There are hundreds of phytoplankton species that are not toxic and regularly bloom in South Australia, due to an upwelling of nutrient-rich water from the depths. "All the way from Ningaloo [Reef, off Western Australia] to New Zealand, we have this long string of blooms that often occur every year, and it's why the southern right whales come to feed, and it's why they have their children here, [because] there is this food source," Coleman says.
South Australia is also in the midst of one of the most severe and long-lasting marine heatwaves on record; the state's environmental protection authority says it has created conditions that have allowed karenia mikimotoi to bloom. In other parts of the world karenia mikimotoi blooms at cooler temperatures. But, according to Coleman, the destruction of oyster reefs, seagrasses and other life on the floor of the Spencer and St. Vincent gulfs either side of the Yorke Peninsula has contributed to the imbalance.
"The hope is that if we can restore the benthic life [deep-sea dwelling marine life] in the gulfs," she says. "We will have more fish, we'll have more life; we'll also have water that is clearer and cooler — and it will reduce our vulnerability." SBS News contacted the South Australian government for comment but did not receive a response.
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