Imagine an underwater forest stretching across an area bigger than England — one that most people have never seen. That’s exactly what scientists at Arizona State University just mapped for the first time: the world’s seagrass meadows.
Using artificial intelligence and satellite images, the research team identified 148,506 square kilometers (about 57,340 square miles) of seagrass globally. That’s a combined area larger than all of England, lying mostly in shallow, subtidal waters around the world.
The scientists, led by Jiwei Li, an assistant professor at ASU’s School of Ocean Futures, spent four years training a deep-learning AI model to spot seagrass from space. Partners worldwide helped verify the findings by diving underwater with cameras to compare against what the satellites showed. The team published their results in the journal Nature.
The map revealed some striking patterns. About 70 percent of all the world’s seagrass grows off the coasts of just five countries: the Bahamas, the United States, Australia, Indonesia, and Cuba. Yet only 21 percent of this vast seagrass habitat falls inside marine protected areas — regions where fishing and development are restricted to help ocean life thrive.
Even more concerning, nearly 80 percent of seagrass loss over the study period happened outside those protected zones, pointing to a clear opportunity for smarter conservation.
Seagrass matters more than most people realize. It’s the ocean’s only flowering plant, forming underwater meadows that shelter fish, dugongs, and sea turtles. It also soaks up carbon dioxide — the gas driving climate change — at a rate 35 times faster than forests on land. Seagrass beds shield coastlines from storms and filter pollutants from the water.
"Seagrass is an underwater rainforest, but it’s not as shiny and colorful as coral reefs," Li told Mongabay. That, he suggests, is why seagrass hasn’t received the same attention — or funding — for research and protection.
The study found that about 4 percent of the world’s seagrass meadows — roughly 5,969 square kilometers — vanished between 2019 and 2024. An additional 6,220 square kilometers in tropical regions were degraded. Threats include hurricanes, marine heat waves, disease, coastal construction, and soil washing off farmland and industrial sites.
But the news isn’t all grim. The maps also spotted recovery in places like South Bay, Los Angeles, and Cuba, where cleaner water allowed seagrass to bounce back. "If the water conditions are good, and there is no disturbance from human activities, it comes back really fast," Li said. "That gives us hope for seagrass conservation."
Li says he hopes the new maps will help governments and conservation groups make smarter, data-driven decisions about where to create new marine protected areas. "Our hope is that these maps enable more data- driven decisions for coastal management and climate mitigation," he said.