Orbital Biosignature Recon: Algae Bloom Chlorophyll Near South Australia

Editor’s note: with the future advent of powerful telescopes that may be able to resolve habitable worlds in images composed of a few pixels, large biological phenomena such as algal bloom on our home world could be visible. The more we know about observing and characterizing them on Earth the better prepared we’ll be to search for them on other worlds as new, more powerful exoplanet observational tools come online. Note in the detailed image below you can see boats and the wakes that they make.

The bloom, first detected in mid-March 2025 around the Fleurieu Peninsula, is caused by the marine dinoflagellate Karenia mikimotoi. For more than five months, it has persisted and fluctuated along the coast. While the algae is not classified as toxic to humans, it can irritate the skin and eyes and may cause respiratory discomfort. For marine life, however, it poses a serious threat, as it can damage the gills of fish and lead to death.

The Government of South Australia has linked the bloom to a prolonged marine heatwave that has been affecting southern Australia since September 2024. Karenia mikimotoi typically thrives in nutrient-rich, stratified waters where light and stability allow it to proliferate.

Yet, the ocean remains a highly complex and dynamic system. This is where satellites orbiting above, like Sentinel-3, play a vital role, providing a broader perspective that helps scientists and decision-makers piece together the full story of events unfolding at the surface.

Astrobiology