A mysterious algae may be behind South Australia's toxic marine crisis! Scientists are pointing to a little-known species called Karenia cristata as the likely culprit producing the harmful brevetoxins in the recent devastating algal bloom. But here's where it gets controversial: this species has never before been spotted in Australian waters.
Groundbreaking research, currently under academic peer review, indicates that Karenia cristata dominated the bloom for most of its duration and was one of five Karenia species present. Of all these, only K. cristata is known to produce brevetoxins, the harmful toxins responsible for the severe impacts on marine life and human health.
Professor Shauna Murray from the University of Technology Sydney (UTS) led the investigation, which began when the bloom first appeared near Victor Harbor beaches in March. The bloom was marked by unusual sea foam, mass fish deaths, and people experiencing acute respiratory symptoms. (https://www.abc.net.au/news/2025-03-18/algae-bloom-likely-cause-fish-deaths-foam/105064874)
Previously, Karenia cristata had only been documented twice off South Africa and once near Newfoundland, Canada, making its presence in Australia an alarming development. The research describes the species as an "emerging international threat with unpredictable consequences in a changing ocean climate."
Professor Murray explained that respiratory issues observed in surfers in March hinted at a brevetoxin-producing species beyond the initially identified Karenia mikimotoi. This suspicion was confirmed in early May when the South Australia Shellfish Quality Program detected brevetoxins in local waters. (https://www.abc.net.au/news/2025-05-08/millions-oysters-quarantined-sa-algal-bloom/105266062) Professor Murray noted, "That was when we realized we were dealing with a completely different Karenia species in this bloom."
A race against time
Identifying the exact algal species was no small feat. Professor Murray described the work as "incredibly fast" compared to the typical multi-year timeline such research usually requires. This rapid progress was possible thanks to a large, dedicated team and a highly coordinated effort across 39 sampling sites.
She emphasized that Karenia blooms are rarely made up of just one species; they usually contain a mix, with dominance shifting over time and across different locations. While K. cristata was the overall dominant species, other Karenia members took the lead in specific times and places.
The big question: how did Karenia cristata arrive in Australian waters?
Professor Murray admitted that the lack of historical research makes it impossible to pinpoint when or how the species first appeared. "Because we don't know what was there in the past, we can't know if it was there all along," she said. Based on its previous sightings in far-flung locations like Canada and South Africa, she suspects it has likely been part of Australia's "hidden flora"—species that exist in low numbers and have gone largely unnoticed.
Very little is known about the biology of K. cristata, but data from a previous South African bloom suggest it thrives in water temperatures between 14°C and 18°C. Anecdotally, it seemed to follow a similar seasonal pattern in South Australia, proliferating from May onwards when the water was cooler. However, Professor Murray cautioned that more research is required to understand exactly what conditions favor this species.
Misunderstood and underestimated
Professor Murray stressed that the bloom has been "badly misunderstood" and possibly misrepresented since its onset. Identifying K. cristata was just the starting point; significant research remains. Continuous monitoring will be essential not only in South Australia but across the nation, given the potential health risks posed by brevetoxins.
Interestingly, the brevetoxins produced by K. cristata are very similar to those generated by Karenia brevis, which frequently blooms off Florida, USA. The main difference is that the Australian species does not produce BTX-1, a specific chemical form found in the US, though it produces other analogues. Professor Murray noted that little research has yet been done comparing the toxicity of these variants, but she expects their effects to be broadly similar.
What do you think? Could Karenia cristata be an unrecognized, long-standing resident of Australian waters, or is this a new invasive threat in disguise? Share your thoughts in the comments, because understanding this algae could be crucial for both marine ecosystems and public health.
