Artificial intelligence has revealed a striking transformation taking place across the worldโs oceans: enormous floating algae blooms are becoming more widespread.
In the first comprehensive global assessment of its kind, scientists analyzed roughly 1.2 million satellite images and found that both floating microalgae and large mats of macroalgae have expanded significantly over the past two decades.
The findings suggest that changing ocean temperatures, shifting currents, nutrient pollution, and natural climate variability may be creating increasingly favorable conditions for floating algae.
While some of these blooms can provide valuable habitat for marine life, their rapid expansion could also bring serious consequences when they reach coastlines โ including ecological damage, foul odors, threats to human and animal health, disruptions to tourism, and substantial economic losses.
The research, led by scientists from the University of South Florida and the National Oceanic and Atmospheric Administration, was published in Nature Communications.
AI uncovers a global change in the oceans
Scientists have studied major algae outbreaks in individual regions for years, but obtaining a reliable global picture has been much more difficult.
Floating algae can be challenging to detect from space because they often occupy only a tiny fraction of individual satellite pixels. Sorting through decades of imagery manually would also require an enormous amount of time.
Artificial intelligence changed that.
Researchers trained a deep-learning system to recognize subtle spectral and visual signals associated with algae floating at the ocean surface. The technology allowed the team to examine satellite records spanning approximately two decades and covering 13 major ocean regions.
According to senior author Chuanmin Hu, professor of oceanography at the University of South Florida College of Marine Science, the study provides a global view of both floating macroalgal mats and microalgal surface accumulations.
The results point toward an ocean increasingly favorable to floating macroalgae.
Floating algae are expanding worldwide
The researchers examined changes between 2003 and 2022 and found significant increases in both major types of floating algae.
Surface microalgal blooms increased globally at an average rate of about 1% per year.
Macroalgae showed even more dramatic growth in some regions.
In parts of the tropical Atlantic and western Pacific, floating macroalgae expanded by approximately 13.4% annually, with some of the largest increases occurring after 2008.
Over the study period, the cumulative area affected by detected microalgal blooms reached approximately 43.8 million square kilometers, or about 16.9 million square miles.
The scale of that expansion suggests that major changes are taking place at the ocean surface.
Something changed after 2008
One of the most striking findings was the timing of the expansion.
Before 2008, exceptionally large macroalgal blooms were relatively uncommon outside areas such as the Sargasso Sea.
Then a series of major events began appearing in different parts of the world.
In 2008, a massive bloom of the green seaweed Ulva emerged in the Yellow Sea.
In 2011, enormous quantities of Sargassum appeared across the tropical Atlantic.
Another major bloom developed in the East China Sea in 2012.
Taken together, these events suggest that the global ocean may have crossed an important ecological threshold.
Researchers describe the trend as a possible shift from an ocean historically poor in large floating macroalgal blooms toward one where such blooms are increasingly common.
That possibility could have major implications for marine ecosystems.
Floating seaweed can be both habitat and hazard
Not all floating algae are harmful.
In the open ocean, mats of seaweed can create floating ecosystems that provide shelter, feeding grounds, and nursery habitats for fish, invertebrates, and other marine organisms.
These floating communities can enhance biodiversity and potentially support fisheries.
But the situation changes dramatically when enormous quantities of algae wash ashore.
Thick accumulations of decaying seaweed can smother coastal habitats and degrade water quality.
As the organic material decomposes, it can consume oxygen and release unpleasant or potentially harmful gases.
Massive strandings can also overwhelm beaches, ports, and tourism infrastructure, requiring costly cleanup operations.
Coastal communities that depend heavily on tourism and fishing can therefore face substantial economic consequences.
The rapidly growing Sargassum problem in parts of the tropical Atlantic and Caribbean is one prominent example of how floating algae can shift from being an offshore ecosystem resource to a major coastal challenge.
1.2 million satellite images reveal the bigger picture
To detect these changes, the researchers turned to an extraordinary volume of satellite observations.
Their dataset contained approximately 1.2 million images covering oceans around the globe.
The team divided the ocean into 13 geographic regions and analyzed five different categories of floating algae.
The artificial-intelligence model was trained using millions of image features so that it could recognize the faint signals produced by algae at the surface.
This was particularly challenging because algae may stretch across broad areas while still occupying less than 1% of an individual satellite pixel.
First author Lin Qi, an oceanographer at NOAAโs Center for Satellite Applications and Research, adapted a computer model previously developed by the research group so that it could process the much larger global dataset.
Training and running the model took months.
Supercomputing made the global analysis possible
Even with artificial intelligence, analyzing more than a million satellite images required enormous computing power.
The researchers relied on the University of South Floridaโs Research Computing facility, where high-performance computers could process multiple groups of satellite images simultaneously.
Despite that capability, completing the global analysis still required several months.
The project demonstrates how AI and high-performance computing are beginning to transform Earth observation.
Satellite archives now contain decades of data about the oceans, atmosphere, and land surface. Machine-learning systems can search those records for patterns that would be extremely difficult for researchers to identify manually.
In this case, AI helped reveal a global ecological trend that had previously been observed mainly through separate regional studies.
Why are algae blooms increasing?
The study does not point to a single universal cause.
Instead, the expansion of floating algae appears to be influenced by a combination of environmental and human factors that differ between regions.
One important factor is nutrient enrichment.
Fertilizers and other nutrient-rich runoff from agriculture, cities, and rivers can deliver nitrogen and phosphorus to coastal waters. These nutrients can stimulate rapid algae growth when conditions are favorable.
Ocean warming may also play a role.
Higher temperatures can influence algae growth directly while altering circulation patterns, nutrient availability, and the boundaries of suitable habitats.
Changing currents can transport algae into new areas or concentrate floating biomass into enormous mats.
Natural climate variations may further amplify or suppress blooms from year to year.
The researchers emphasize that different regions may therefore be experiencing algae expansion for different reasons.
A possible new era of algae-rich oceans
The scale and timing of the changes raise a larger question: Are the worldโs oceans undergoing a long-term ecological regime shift?
The sharp expansion of macroalgae since the late 2000s suggests that conditions across several ocean basins have become increasingly favorable for large floating blooms.
If the trend continues, massive algae mats could become a more familiar feature of ocean environments and coastal regions around the world.
That would bring a complicated mixture of benefits and risks.
Offshore, floating algae can support diverse communities of marine organisms.
Nearshore, excessive accumulations can damage ecosystems, reduce water quality, affect public health, disrupt fisheries, and overwhelm tourism-dependent beaches.
The challenge for scientists will be understanding where blooms are likely to occur, what drives them, and how their impacts may change as ocean conditions continue to evolve.
AI could help scientists track what happens next
Researchers now plan to examine additional satellite datasets to better understand the causes behind the global expansion.
Longer records and improved AI models could help scientists determine how closely algae blooms are connected to ocean warming, nutrient pollution, river discharge, changing currents, and major climate cycles.
They may also make it possible to develop better forecasting systems.
Early detection of large algae mats could give coastal communities more time to prepare for strandings, protect sensitive ecosystems, and organize cleanup efforts.
The study therefore represents more than a discovery about algae.
It demonstrates how artificial intelligence can turn vast satellite archives into a powerful tool for monitoring planetary change.
And what those satellites are revealing is striking: across much of the global ocean, floating algae are no longer behaving as they once did.
The oceans may be entering a distinctly more algae-rich era.
Journal reference
Lin Qi, Menghua Wang, Brian B. Barnes, Douglas G. Capone, Joaquim I. Goes, Edward J. Carpenter, Yuyuan Xie, and Chuanmin Hu. Global floating algae blooms are expanding. Nature Communications 17 (2025). DOI: 10.1038/s41467-025-66822-5.