A significant toxic algal bloom in South Australia, caused by the microalgae Karenia mikimotoi, is now starting to dissipate, but concerns remain about its potential return in the coming months and years, which could result in long-term ecological damage. Since March, this unusual bloom has led to the deaths of at least 200 marine animals and has discoloured waters and foam in areas including the Fleurieu Peninsula, Kangaroo Island, Yorke Peninsula, and the Coorong.
The South Australian Department of Environment has indicated that there is currently no natural method to mitigate the bloom, which has been exacerbated by an ongoing marine heatwave and calm conditions, although the cooler winter temperatures have begun to aid in its reduction. However, as conditions warm up again in summer, the Karenia mikimotoi could become active once more, potentially multiplying rapidly. According to Grant Pelton, the Department’s Director of Strategic Projects, these algae can enter a dormant state, producing cysts that sit on the seafloor until favourable conditions arise—such as increased light, warm water, and sufficient nutrients.
Pelton warned that climate change is likely to increase the frequency and severity of such algal blooms, with risks of altering marine ecosystems and reducing biodiversity. Authorities are closely monitoring this situation and are implementing plans for early detection to manage future blooms more effectively. They are also collaborating with state and federal agencies and international counterparts in the US and Japan, who have experience dealing with similar hazardous algal events.
The recent bloom is noted to be unprecedented in size and scale for South Australia, potentially on par with the largest algal blooms ever recorded in the country. It has affected a diverse range of marine species, including fish, sharks, rays, and seahorses, highlighting the extensive ecological impact. Previous incidents of this type of algae were limited, with the last significant occurrence in Coffin Bay in 2014, but the current event is proving far more pervasive. As authorities anticipate future blooms, continued research and vigilance are paramount to safeguard marine life and the surrounding environment.