A new AI-driven analysis reveals that floating algae are rapidly spreading worldwide, marking a potential transformation in ocean biology. Credit: Shutterstock

Machine learning reveals that ocean conditions are increasingly becoming more favorable for macroalgae growth.

For the first time, researchers using artificial intelligence have carried out a global analysis of floating algae and found that blooms are increasing across the world’s oceans.

The study links this expansion to changes in ocean temperature, currents, and nutrient levels, and suggests the trend could have wide-ranging effects on marine ecosystems, tourism, and coastal economies.

The work was led by scientists from the University of South Florida and the National Oceanic and Atmospheric Administration and highlights how artificial intelligence can process vast ocean datasets.

Sargassum observed during a sampling cruise. Credit: Sully Sullivan

Global shift toward algae growth

“While regional studies have been published, our paper gives the first global picture of floating algae, including macroalgal mats and microalgal scum,” said Chuanmin Hu, professor of oceanography at the USF College of Marine Science and senior author of the paper published in Nature Communications.

“Our results show that the global ocean now favors the growth of floating macroalgae.”

Floating algae types Credit: Qi et al

Hu describes macroalgae, such as seaweed, as having both benefits and risks. In open ocean environments, they provide important habitat for marine species and support fisheries by acting as nursery areas.

However, when these algae drift into coastal regions, the decaying material can damage tourism, local economies, and the health of both people and marine life.

From 2003 to 2022, researchers observed growth in both microalgal surface films and larger macroalgal mats worldwide.

Satellite image of Ulva macroalgae in the Yellow Sea. Credit: NOAA Star

Microalgae increased at a steady rate of about one percent per year. In contrast, macroalgae blooms expanded much more rapidly, rising by 13.4 percent annually in the tropical Atlantic and western Pacific, with the sharpest increases occurring after 2008.

The total area covered by microalgal blooms reached 43.8 million square kilometers (16.9 million square miles), marking a departure from historical patterns.

Key turning points in macroalgae expansion appeared around 2010. A major bloom of the green seaweed Ulva occurred in the Yellow Sea in 2008, followed by a large bloom of brown sargassum in the tropical Atlantic in 2011. Another sargassum event was recorded in the East China Sea in 2012.

Large Sargassum field. Credit: Ellen Park — Woods Hole Oceanographic Institution

“Before 2008, there were no major blooms of macroalgae reported except for sargassum in the Sargasso Sea,” Hu said. “On a global scale, we appear to be witnessing a regime shift from a macroalgae-poor ocean to an macroalgae-rich ocean.”

AI enables global ocean analysis

To complete the study, Hu and colleagues applied artificial intelligence to analyze 1.2 million satellite images, covering 13 ocean regions and five types of algae. A deep learning model was trained to detect subtle visual signals of algae on the ocean surface. These signals often span multiple pixels but usually account for less than one percent of each individual pixel.

These figures show the change in density of global floating algae in the 20 years between 2003 and 2022. Credit: Qi et al

Lin Qi, an oceanographer at the NOAA Center for Satellite Applications and Research and first author of the study, refined an existing model developed by the team to process two decades of global ocean imagery. Training the model required several months and the analysis of millions of image features.

The researchers also highlighted the role of USF’s Research Computing facility, which provided high-performance systems capable of processing multiple image sets simultaneously. Even with this infrastructure, analyzing the full dataset of 1.2 million images required several months.

“This work is impossible without the high-performance computing facility or the long-term collaborations between NOAA and USF,” Qi said.

Macroalgal mats can serve as valuable habitat for many marine species, such as this sargassum fish. Credit: Ocean Image Bank — Lorenzo Mittiga

Climate and human activity drive change

The study concludes that both human activity, such as nutrient runoff into the ocean, and climate-related changes, including ocean warming, are contributing to the expansion of algae blooms. The authors note that the specific drivers may vary by region.

Looking ahead, Qi said, “We are going to explore more satellite data and look for a better understanding of the expansions.”

Reference: “Global floating algae blooms are expanding” by Lin Qi, Menghua Wang, Brian B. Barnes, Douglas G. Capone, Joaquim I. Goes, Edward J. Carpenter, Yuyuan Xie and Chuanmin Hu, 7 December 2025, Nature Communications.
DOI: 10.1038/s41467-025-66822-5

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