An analysis of 1.2 million satellite images powered by artificial intelligence has uncovered a massive expansion of floating seaweed across the world’s oceans, which scientists say could damage and reshape marine habitats and coastal ecosystems. 

The study, led by researchers at the University of South Florida (USF) and the US National Oceanic and Atmospheric Administration (NOAA), provides the first comprehensive global assessment of floating algae. 

Professor Chuanmin Hu, senior author from the USF College of Marine Science and his colleagues used artificial intelligence to examine 1.2 million satellite images covering the global ocean. Their analysis included 13 geographic zones and five categories of algae.

The team trained a deep learning model to recognise subtle visual signals associated with algae floating at the surface. These algae features often extend across many pixels, yet they usually account for less than one per cent of an individual pixel.

The findings, published in Nature Communications, reveal that while surface microalgae expanded at a steady rate of one per cent annually, large floating seaweed – known as macroalgae – has surged dramatically.

In the tropical Atlantic and western Pacific, macroalgal mats expanded by an average of 13.4 per cent each year, with cumulative bloom coverage reaching 43.8 million square kilometres.

Researchers identified 2008 as a pivotal turning point for global waters. Before then, extensive macroalgae blooms were largely restricted to Sargassum in the Sargasso Sea. However, a huge bloom of green Ulva seaweed emerged in the Yellow Sea in 2008, followed by unprecedented Sargassum surges across the tropical Atlantic in 2011 and the East China Sea in 2012.

Professor Chuanmin Hu said the trend represents a double-edged sword for the environment. 

On the high seas, floating weed mats serve as critical nursery grounds and feeding habitats for marine life. 

But, when ocean currents transport these colossal masses to land, the consequences are negative and severe: the vegetation decays along shorelines, releasing toxic, foul-smelling gases, smothering coastal ecosystems, disrupting local fisheries and severely impacting tourism.

Scientists have linked the global proliferation to a combination of anthropogenic factors and climate variability. Intensifying agricultural nutrient runoff entering waterways, along with warming ocean temperatures and shifting ocean currents, is creating ideal conditions for rapid growth. 

The research team emphasised the importance of AI in tracking these discoveries.

Lin Qi, an oceanographer at the NOAA Center for Satellite Applications and Research and first author of the study, said that looking forward “we are going to explore more satellite data and look for better understanding of the expansions.”

Click here for more from the Oceanographic Newsroom