The current harmful algae bloom (HAB) in South Australia, a number of species within the Karenia family, some of which produce brevetoxins ((marine neurotoxins) including Karenia cristata. This HAB is the largest and most destructive algal bloom in Australia’s history and it 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. It is the most significant marine mortality events on the great southern reef in living memory.
Though the coastal water can be clear along the beach it has been stripped of biodiversity and marine life. If you walk along the coastal path between Rosetta Head and Kings Head you can see the HAB sitting in the sea just off the coast:
It comes and goes. Looking back we can see that that the initial SA Government response and messaging about the harmful algae bloom were fragmented and confusing for stakeholders, and that there were delays in both the Commonwealth and state governments' responses. The concerns of the local community on the southern Fleurieu Peninsula were not heeded until the bloom reached the Adelaide metropolitan beaches.
Karenia cristata is the primary source of brevetoxins and this species produces high levels of neurotoxins -- hence Kalani's death from eating dead fish and the distressed and paralysed western grey kangaroos at Tunkakilla on the southern Fleurieu Peninsula who were close to the toxic algae bloom.
UTS’s Professor Shauna Murray, who who first identified the Karenia cristata species for producing brevetoxins in Australian waters in November 2025 observes: “We isolated Karenia cristata cells and grew them in our laboratory and then used a series of molecular genetic methods to dentify 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.”