The latest global remote sensing study using artificial intelligence technology shows that floating algae on the surface of the world's oceans are rapidly expanding, indicating that marine biological systems may be undergoing a profound transformation. The research team pointed out that this trend is closely related to changes in seawater temperature, ocean currents, and nutrient patterns, and may have widespread impacts on marine ecology, tourism, and coastal economies in the future. The research, led by scientists from the University of South Florida and the National Oceanic and Atmospheric Administration (NOAA), highlights the critical role of artificial intelligence in processing extremely large-scale ocean observation data.
This is the first time that researchers have systematically analyzed floating algae on the sea surface on a global scale, covering large macroscopic algae rafts and microalgae surface films, and provided an overall picture of their distribution and changes over the past two decades. Hu Chuanmin, corresponding author of the paper and professor of oceanography at the University of South Florida School of Marine Science, said that the research results show that today’s global marine environment is generally more conducive to the growth of floating macroalgae. He pointed out that in the high seas environment, macro-algae such as seagrass and brown algae can provide habitats for a variety of marine organisms and serve as important nursery sites for fisheries, which has a positive ecological effect. But once these algae masses are transported to coastal areas by ocean currents, their massive death and decay will cause damage to the tourist landscape, impact the local economy, and threaten the health of coastal residents and marine life.
The study used satellite observation data from 2003 to 2022 and found that both microalgae films and floating macroalgae clusters on the sea surface are increasing globally. Statistics show that the coverage area of microalgae is steadily increasing at a rate of about 1% per year, while macroalgae are expanding much more rapidly in some sea areas. In the tropical Atlantic and Western Pacific regions, the annual growth rate is as high as 13.4%, especially after 2008, the growth rate accelerated significantly. By the end of the study period, the total area of global sea surface microalgae outbreak areas had reached 43.8 million square kilometers (approximately 16.9 million square miles), significantly deviating from the previous historical distribution pattern. The research team believes that these numbers point to a "regime transition" from a "macroalgae-poor" ocean to a "macroalgae-rich" ocean.
Judging from the timeline, large-scale outbreaks of macroscopic floating algae appeared at multiple key turning points around 2010. In 2008, the Yellow Sea recorded the first large-scale green algae outbreak of Enteromorpha; in 2011, a large-scale brown algae Sargassum outbreak occurred in the tropical Atlantic; and in 2012, another large-scale Sargassum event occurred in the East China Sea. Hu Chuanmin pointed out that before 2008, except for Sargassum in the traditional sense, almost no other area had experienced such a large-scale outbreak of floating macroalgae. Now, similar events are recurring in multiple ocean regions, giving researchers reason to believe that the global ocean is entering a new phase characterized by high abundance of floating macroalgae.
The key to completing this work lies in the application of artificial intelligence technologies such as deep learning. The research team trained a deep learning model for 13 typical sea areas and 5 different types of floating algae to identify approximately 1.2 million satellite ocean images pixel by pixel. Floating algae often only account for a very small part or even less than 1% of a pixel in a single satellite image, and their spatial distribution is highly fragmented, so they are easily overwhelmed by noise under traditional algorithms. By automatically extracting and classifying subtle “visual signals,” the AI model is able to screen out traces of these algae that are difficult to identify manually on a global scale.
Qi Lin, the first author of the paper and an oceanographer at the Satellite Application and Research Center of the National Environmental Satellite Data and Information Service (NESDIS), made improvements based on the previous team's model, allowing it to efficiently process 20 years of global ocean remote sensing data. Model training itself takes months and requires analyzing and optimizing millions of image features. The research also relied on the high-performance computing platform provided by the University of South Florida Research Computing Center to achieve parallel processing of multiple sets of images. Even with the support of this infrastructure, it still took several months to complete the analysis task of 1.2 million images. Ziering emphasized that this work would be nearly impossible without this computing platform and the long-term and stable cooperation between NOAA and the University of South Florida.
In terms of driving factors, the study believes that human activities and climate change are the two main causes of the expansion of floating algae outbreaks. Nutrient salt runoff from rivers and coastal areas is continuously transported into the sea, causing the content of nitrogen, phosphorus and other nutrient elements in the sea surface to increase, providing sufficient "fertilizer" for algae. At the same time, global warming has caused the oceans to continue to heat up, changing the stratified structure of seawater and ocean current patterns, creating thermal and dynamic conditions that are more suitable for rapid algae reproduction in some sea areas. The research team pointed out that the specific driving mechanisms may differ significantly in different regions and need to be disassembled with more regional observations and simulations.
From an ecological perspective, floating macroalgae on the one hand provide shelter for a variety of marine life, including sargassum fish, and increase local biodiversity and fishery resources; on the other hand, the large amounts of humus produced when transported to the coast will cause the beach to be "submerged by algae", consume dissolved oxygen and release harmful gases during the decomposition process, exacerbating the risk of eutrophication and hypoxia in coastal water bodies. For coastal communities that rely on seaside tourism, large-scale accumulation of algae not only destroys the landscape, but also drives up cleaning and maintenance costs, causing a chain impact on hotels, restaurants and other related industries. In some low-income coastal areas, such ecological events are compounded by climate stresses, posing additional challenges to the livelihood security of vulnerable communities.
Looking to the future, the research team plans to further integrate more satellite observation data to refine the expansion patterns of different sea areas and different algal species, and try to couple the AI recognition results with numerical ocean models to improve the prediction ability of the formation, drift and landing of floating algal masses. Qi Lin said that the next step will focus on clarifying the relative weight of the main driving factors in each region to provide more targeted scientific basis for coastal governance and adaptive management. According to reports, this study, entitled "Global floating algal blooms are expanding", was published in "Nature Communications" in December 2025, further highlighting the rapid reshaping of the ecological pattern of the ocean surface in the context of climate change.