Karenia cristata, which is the largest and most destructive algal bloom in Australia’s history, on. the beach on. the beach is persisting along parts of the South Australian coastline, a year on from when it was first detected in March 2025.
It has affected 20,000 sq km of coast and resulted in marine mass mortality killing millions of sea creatures – from tiny shellfish to top predators like white sharks. The water can be super clear on the beach but it has been stripped of life.
Karenia cristata is the primary source of brevetoxins and this species produces high levels of neurotoxins -- hence Kalani's death and the distressed and paralysed western grey kangaroos at Tunkakilla on the southern Fleuieu Peninsula who were close to the toxic algae bloom.
According to UTS’s Professor Shauna Murray, who first identified the Karenia cristata species for 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.”
What we know from CSIRO is that the Karenia cristata 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. In 2025 something happened in the environment that made it dramatically increase in abundance. The main theory is warming sea waters from climate change.
The bloom still lingers, 12 months on from March 2025 as it has somehow managed to persist throughout the whole gamut of conditions over the course of a year.as the conditions get more suitable for Karenia cristata and similar seasonal conditions to last year. It thrives in relatively cool, temperate coastal waters as it can persist and dominate in colder water conditions and so thrives in autumn and winter.