News release

From: University of Technology Sydney (UTS)

Researchers find harmful algae species wasn’t new to South Australian waters

The coastline of South Australia has been affected for nearly a year by an unprecedented harmful algal bloom which has led to the deaths of millions of fish and sharks, impacted marine mammals and birds and affected the health of some people.

The origins of this event remain the topic of intense discussion and investigation among both the public and scientific community.

New collaborative research involving the University of Technology Sydney (UTS), the South Australian Research and Development Institute (SARDI), CSIRO, Australia’s national science agency, and the Integrated Marine Observing System (IMOS) has revealed the species of algae dominating this bloom has long been a natural resident in South Australian waters.

During 2025, Karenia cristata was identified as one of the main species dominating the bloom and releasing a biotoxin called brevetoxin. It is a species not previously known to cause such significant impacts on marine ecosystems and had been only recorded twice before anywhere in the world.

According to UTS’s Professor Shauna Murray, who first identified this species as the culprit producing brevetoxins in Australian waters, “We isolated Karenia cristata cells and grew them in our laboratory and then used a series of molecular genetic methods to identify and quantify them in South Australian waters since March 2025. We found K. cristata cells were producing high levels of brevetoxins, which hadn’t been known before.”

The sudden emergence of K. cristata and its unprecedented impacts have raised concerns and debate among the public about where it has come from. Now, by using archived DNA retrieved from seawater samples managed by CSIRO and collected during the past decade by IMOS, the research team has shown that the harmful species has had regular, albeit low levels of presence in South Australian waters since sampling began in 2016, but that during 2025 there was a massive increase in its abundance.

Professor Justin Seymour, who leads the Ocean Microbiology Group within the Climate Change Cluster at UTS, said, “After helping to identify the species dominating the bloom, we were next keen to work out its origins in an effort to understand why it has apparently appeared all of a sudden with such devastating impacts.”

The research team took advantage of a library of archived DNA samples that had been collected near Kangaroo Island as part of the IMOS Marine Microbiome Initiative, which has been using genomic techniques to characterise the microbiology of marine environments around the Australian continent for more than 10 years.

CSIRO researcher and leader of the IMOS Marine Microbiome Initiative Dr Jodie Van De Kamp said, “A fundamental part of our program is the long-term storage of DNA samples. This enabled us to go back and analyse this extensive, decade-long collection, providing a window into past conditions and increasing our understanding of the current algal blooms in South Australia. We don’t always know which rare members of the microbiome may one day become problematic, nor do we always have the tools to measure them. The value of these archived DNA samples and the important role of the IMOS Marine Microbiome program is that it provides vital insights for understanding current conditions and managing future challenges.”

When analysed using new approaches developed to identify K. cristata, it was found that this harmful algal species was always present during the entire period that samples have been collected in South Australian waters.

“However, in 2025 something happened in the environment that made it dramatically increase in abundance. Finding out what caused this increase is our next objective,” said Professor Seymour.

Researchers at SARDI are now linking this historical data with measurements of ocean conditions in an attempt to tease out the processes leading to its increased occurrence, using a forensic oceanographic approach.

Associate Professor Mark Doubell, Oceanography Subprogram Leader at SARDI, is leading this effort. “Understanding the environmental conditions and locations associated with the presence of these harmful algae will provide critical capacity for early identification, tracking and the forecasting of blooms,” he said.

Professor Murray said pinning down the causes of this devastating event is likely to be very complex. “There are multiple ecological factors influencing the growth of K. cristata, beyond oceanographic conditions. It might be some time before we untangle all of them. This first step in finding K. cristata in samples from a number of years ago is important, and we are now finalising the analysis of these data to submit them for peer review.”

This work has nonetheless solved one of the mysteries surrounding the South Australian harmful algal bloom, the Executive Director of IMOS, Dr Michelle Heupel said. “The challenges facing Australia’s oceans are immense. IMOS delivers sustained ocean observations that underpin the collaborative research crucial for understanding events such as the harmful algal bloom in South Australia and assist with forecasting of similar events and their impacts on marine ecosystems.”