A harmful algal bloom (HAB) has been causing widespread marine mortality and habitat damage in South Australia, triggered by a combination of environmental factors including nutrient upwellings, flood discharges, heatwaves, calm seas, and decomposing marine vegetation.
More than 12,000 observations across over 400 species have been submitted to the SA Marine Mortality Events project on iNaturalist by divers, fishers, beachgoers, and coastal residents. Mass deaths of fish, sharks, rays, invertebrates, and seabirds have been recorded along large sections of South Australia’s coastline, including parts of the Spencer Gulf, the head of Gulf St Vincent, the metropolitan Adelaide beaches and the Coorong. There is also new evidence that the bloom is spreading into Adelaide Metropolitan waterways, including the Port River, home to the Adelaide Dolphin Sanctuary.
The South Australian community have driven data collection efforts through citizen science, playing a vital role in tracking the spread and impact of the bloom and assisting scientists in trying to understand this phenomenon. Uploads to iNaturalist and social media have also served as a key tool for public collaboration, communication and real-time data on marine deaths.
Without this large-scale citizen involvement, the true scale of the bloom’s ecological damage is very likely to have been underreported. The full environmental toll is still unfolding, with long-term ecological consequences likely.
Learn more about the HAB in the new comprehensive article by Janine Baker on the GSRF website.
https://greatsouthernreef.com/2025-algal-bloom-june-update
Learn more about the Science of the Algal Bloom through this webinar recording from the Port Environment Centre
View all observations contributed by citizen scientists on the INaturalist project
https://www.inaturalist.org/projects/sa-marine-mortality-events-2025
