The Science Behind South Australia's Harmful Algal Bloom

This presentation examines the science underpinning South Australia's harmful algal bloom, drawing on the multidisciplinary research.
About this Event

In March 2025, South Australia experienced the emergence of an unprecedented harmful algal bloom (HAB) that ultimately affected thousands of kilometres of coastline and had significant ecological, social and economic consequences. Dominated by species of Karenia, the bloom resulted in widespread mortality of fish and other marine organisms, disrupted commercial and recreational activities, and prompted one of Australia's largest coordinated marine environmental responses. While harmful algal blooms occur naturally around the world, the scale, duration and impacts of this event highlighted the importance of understanding the biological and environmental processes that drive these increasingly complex marine phenomena.

This presentation examines the science underpinning South Australia's harmful algal bloom, drawing on the multidisciplinary research and operational response undertaken by the South Australian Government in collaboration with universities, national research organisations and industry partners. It explores the biology and ecology of Karenia, the mechanisms by which these microscopic algae affect marine life, and the environmental conditions that are understood to have contributed to bloom development and persistence, including nutrient enrichment, oceanographic processes and the prolonged marine heatwave affecting southern Australia.

The presentation also demonstrates how multiple scientific disciplines were integrated to characterise the bloom and inform management responses. Oceanographic observations, satellite remote sensing, water-quality monitoring, molecular diagnostics, ecological surveys and predictive modelling collectively provided an increasingly comprehensive understanding of bloom dynamics and impacts. These approaches supported evidence-based decision making while highlighting the value of coordinated monitoring and adaptive scientific investigation during a rapidly evolving environmental event.

Beyond documenting an extraordinary bloom, the South Australian experience provides valuable insights into building national capability for harmful algal bloom research and preparedness. It demonstrates the importance of sustained environmental observations, emerging monitoring technologies and collaborative research networks in improving our capacity to detect, understand and respond to future marine ecosystem threats, while identifying key scientific questions that remain the focus of ongoing research.