Arizona State University Maps Global Seagrass to Advance Climate Mitigation and Marine Ecosystem Conservation
Seagrass meadows rank among the most productive and ecologically valuable habitats on Earth, yet they have remained largely invisible in global conservation strategies. For decades, scientists and policymakers lacked a comprehensive understanding of where these underwater plant communities grow, how much area they cover, and how their extent changes over time. That gap in knowledge has now been closed. Researchers at Arizona State University have produced the first high-resolution global map of seagrass ecosystems, providing a critical tool for seagrass conservation, marine ecosystem management, and climate mitigation worldwide.
Understanding the Ecological Value of Seagrass Meadows
Seagrass is frequently confused with seaweed, but the two organisms differ fundamentally. Seaweed is a type of algae that attaches to surfaces but lacks true roots, stems, or leaves. Seagrass, by contrast, is a fully rooted flowering plant that grows underwater in shallow coastal zones. It produces leaves, flowers, and seeds, and its root systems anchor sediment to the ocean floor. This distinction matters because the root structure of seagrass is what gives it such remarkable capacity for shoreline stabilization and carbon storage.
When seagrass grows, it captures carbon dioxide from the water through photosynthesis. When the plant dies, its organic matter is buried in the sediment, where it remains trapped by the root systems of subsequent generations. According to estimates derived from the new global map and complementary sediment carbon data, seagrass ecosystems store approximately 640 teragrams of carbon in the top 30 centimeters of sediment alone. That volume is roughly equivalent to the annual carbon dioxide emissions of 500 million passenger vehicles. Because ocean sediment often extends far deeper than 30 centimeters, the actual carbon stored by seagrass is likely substantially higher.
Beyond carbon sequestration, seagrass meadows perform a range of ecological services. Their root networks prevent coastal erosion by holding sediment in place, reducing the impact of storms and wave action on shorelines. The dense leaf canopies filter pollutants from the water column, improving clarity and quality. These meadows also serve as nurseries and habitat for a wide variety of marine species, including commercially important fish and shellfish. For coastal communities that depend on fisheries for food security and income, the health of nearby seagrass beds has direct economic consequences.
The Persistent Challenge of Mapping Underwater Ecosystems
Mapping terrestrial forests is relatively straightforward. Satellites can capture high-resolution images of tree canopies, and researchers have decades of experience classifying land cover from space. Underwater environments present far greater difficulties. Water absorbs and scatters light, particularly at deeper levels, which degrades the quality of satellite imagery. Seagrass grows at varying densities and can be easily confused with other benthic features such as algae, sand, or coral. Prior to this effort, global seagrass estimates varied widely because different research groups used inconsistent methods, different spatial resolutions, and limited ground-truth data.
The team at Arizona State University’s Center for Global Discovery and Conservation Science recognized that existing approaches were insufficient. The center had previously led the Allen Coral Atlas project, which produced the first global map of shallow-water coral reefs. When researchers attempted to incorporate seagrass data into those coral maps, they found that the tools and models developed for coral detection could not be directly applied to seagrass. A new methodology was required.
How Arizona State University Built the First Complete Seagrass Map
Lead author Jiwei Li, an assistant professor in ASU’s School of Ocean Futures, assembled a team that combined field research, artificial intelligence, and high-performance computing to solve the mapping problem. The process began with divers and field researchers around the world who visited coastal sites and recorded the presence or absence of seagrass, along with other underwater features such as rock, coral, algae, and sand. Each observation was tagged with precise geographic coordinates, creating a dataset of verified ground-truth points.
This ground-truth data was used to train a deep learning model to recognize seagrass in satellite imagery. The model learned to distinguish seagrass from other benthic cover types based on spectral signatures and spatial patterns visible in the satellite data. Once trained and validated, the model was applied to millions of satellite images covering the world’s coastal waters. The computational demands of this task were substantial, and the team relied on ASU’s Agave and Sol supercomputers to process the deep learning workloads at scale.
The resulting map can detect seagrass presence at a spatial resolution of 10 square meters and classify whether the coverage is dense or sparse. Current satellite capabilities limit reliable detection to depths of approximately 30 meters, which covers the vast majority of seagrass habitat since the plants require sunlight for photosynthesis. However, some seagrass species grow at depths of up to 40 meters, and the researchers note that future hyperspectral satellites may extend the mapping capability into deeper waters.
Key Findings: Where Seagrass Grows and How It Is Changing
The map reveals that seagrass distribution is highly concentrated. Nearly 70 percent of the world’s seagrass is located off the coasts of just five countries: the United States, the Bahamas, Cuba, Australia, and Indonesia. This concentration means that conservation actions taken by a small number of nations can have an outsized impact on global seagrass health.
To assess change over time, the researchers compared satellite data from 2019–2020 with data from 2023–2024. They found that approximately 4 percent of mapped seagrass was lost over this four-year period, a rate of about 1 percent per year. The losses were not distributed evenly. The study identified specific drivers in different regions, including coastal development in China and nutrient pollution from agricultural fertilizers in Florida. Climate-related stressors also contributed in certain areas, such as Hurricane Dorian’s impact in the Bahamas and a marine heat wave affecting seagrass in Australia. The researchers caution that longer time series are needed to draw firm conclusions about the relationship between climate events and seagrass loss.
Implications for Marine Protected Areas and the 30×30 Framework
One of the most significant policy-relevant findings from the study concerns the relationship between seagrass loss and marine protected areas. The data shows that only about 21 percent of global seagrass currently falls within designated marine protected areas. More strikingly, nearly 80 percent of the seagrass loss documented during the study period occurred outside these protected zones. This correlation strongly suggests that marine protected areas are effective at conserving seagrass and that expanding protected area coverage to include more seagrass habitat would yield measurable conservation benefits.
These findings are directly relevant to the Kunming-Montreal Global Biodiversity Framework, which includes the 30×30 target of protecting 30 percent of the planet’s land and ocean areas by 2030. Conservation experts have noted that more than half of known seagrass beds remain unprotected, making them high-priority targets for inclusion in new marine protected area designations. The global seagrass map provides the spatial data needed to make those designations strategic and evidence-based.
Conservation Success Stories and Restoration Potential
While the overall trend of seagrass loss is concerning, the map also documents areas where seagrass has expanded or recovered. In South Bay near Los Angeles, seagrass increased as a result of an active restoration project. In Cuba, improved water clarity allowed seagrass meadows to expand. These cases demonstrate that targeted interventions can reverse seagrass decline and that the new map can help identify where similar efforts would be most effective.
A practical advantage of seagrass conservation, compared to coral reef restoration, is the speed at which seagrass can recover. Coral reefs can take decades to regrow after damage, but seagrass grows quickly and can re-establish coverage in a fraction of that time. This characteristic makes seagrass restoration a relatively high-return investment for coastal management agencies. The researchers emphasize the need for additional studies on seagrass growth rates and recovery dynamics to inform future management decisions.
Integrating Seagrass into Climate Policy and Carbon Markets
Before the creation of this map, the absence of reliable spatial data on seagrass extent made it difficult to incorporate these ecosystems into climate policy frameworks and carbon market mechanisms. Accurate baselines are essential for carbon crediting programs, which require verifiable measurements of carbon stocks and changes over time. By providing a consistent, high-resolution baseline, the global seagrass map enables seagrass carbon to be included in climate mitigation accounting with greater confidence.
Greg Asner, director of the Center for Global Discovery and Conservation Science and a co-author of the study, noted that the seagrass map is being integrated into the Allen Coral Atlas monitoring systems. This integration will allow seagrass data to inform a range of planning activities, including marine protected area design, carbon market development, biodiversity conservation prioritization, and even law enforcement against illegal coastal activities.
The Future of Seagrass Monitoring and Research
The publication of this global map marks a transition point rather than an endpoint. The research team plans to continue updating the map as new satellite imagery becomes available, enabling near-real-time monitoring of seagrass change. Advances in satellite technology, particularly the deployment of hyperspectral sensors, will improve the ability to detect seagrass at greater depths and with higher taxonomic resolution. There is also significant potential for integrating seagrass monitoring with other coastal data layers, such as water quality measurements, coastal development patterns, and fishery catch data, to build a more complete picture of the drivers of seagrass change.
For the scientific community, the map opens new avenues for research. Ecologists can now examine seagrass distribution patterns in relation to environmental variables at a global scale. Conservation biologists can use the data to prioritize restoration sites based on factors such as connectivity, threat intensity, and carbon storage potential. Social scientists can analyze the relationship between seagrass proximity and human well-being in coastal communities.
Conclusion
The first complete global map of seagrass represents a fundamental advance in marine science and coastal management. By making the extent and change of seagrass ecosystems visible and quantifiable, Arizona State University researchers have provided the foundation for more effective conservation action, more accurate climate accounting, and more informed policy decisions. The finding that most seagrass loss occurs outside protected areas underscores the urgency of expanding marine conservation coverage. At the same time, documented recovery in places like Los Angeles and Cuba demonstrates that decline is not inevitable when the right conditions are created.
Seagrass has long been overlooked in favor of more visible marine ecosystems like coral reefs and mangrove forests. This map ensures that seagrass can no longer be treated as an afterthought in ocean conservation. For policymakers, researchers, and conservation practitioners, the question is no longer where seagrass grows. It is what actions will be taken to protect it.
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