A groundbreaking international study, spearheaded by the Centre for Advanced Studies of Blanes (CEAB-CSIC) and published in the prestigious journal Nature Communications, has unveiled the first comprehensive global assessment of blue carbon accumulated within the living biomass of seagrass meadows. This pioneering research quantifies the enormous carbon storage capacity residing within the leaves, rhizomes, and roots of seagrass plants worldwide, estimating that these living components alone trap up to 40 million tonnes of carbon. Importantly, this figure excludes the substantial carbon stored in the seabed beneath these meadows, which can remain sequestered for millennia provided the meadows remain intact and undisturbed. Despite occupying a relatively minuscule fraction of the ocean floor, these underwater ecosystems emerge as pivotal players in the global carbon cycle, demonstrating extraordinary efficiency in capturing atmospheric carbon dioxide (CO₂), converting it via photosynthesis into organic matter, and effectively locking it away.
The multinational research consortium, including experts from institutions such as Edith Cowan University, the University of Western Australia, James Cook University, the Institute of Marine Sciences (ICM-CSIC), King Abdullah University of Science and Technology (KAUST), and Argentina’s Institute of Marine and Coastal Research (CONICET), undertook this extensive analysis to create what can be described as the first global inventory of seagrass blue carbon stocks. This assessment encompasses not only the quantification of captured atmospheric CO₂ but also evaluates net primary production—the rate at which seagrass plants convert carbon dioxide into new biomass—and the total carbon stored within their tissues. The study further scrutinizes carbon emissions associated with seagrass loss, highlighting the ecological and climatic consequences of their decline.
What sets this research apart is its multiscalar approach, offering comprehensive data that span regional, national, and local scales, and distinguishing seagrass meadows by their types and geographic locations. Such granularity enables a nuanced understanding of each area’s or ocean’s contribution to carbon sequestration, providing vital insights for policymakers and conservationists. These data empower nations and territories to grasp the value of their own blue forests, fostering informed stewardship over these critical ecosystems that have long been overshadowed beneath ocean waves.
Seagrass meadows, exemplified by genera such as Posidonia, cover an estimated global area ranging between 160,000 and 266,000 square kilometers. Though their physical footprint is modest compared to terrestrial forests, their role as blue carbon sinks is disproportionately significant. Through photosynthesis, seagrasses capture atmospheric CO₂ and transform it into organic carbon incorporated within living biomass structures — their leaves, roots, and rhizomes. Remarkably, a portion of this carbon is transferred into the sediment, where, shielded from aerobic decomposition, it remains locked away for thousands of years, making seagrass meadows among the most enduring and efficient natural carbon storage systems known.
Quantitatively, these blue forests are exceptional. Per hectare, they harbor approximately 1.5 tonnes of organic carbon within their living tissues, while annually fixing close to 7 tonnes of carbon through net primary production. These figures place seagrass meadows on par with, or sometimes surpassing, their terrestrial counterparts like tropical rainforests in terms of carbon sequestration efficiency. This remarkable efficiency owes much to seagrasses’ aquatic environment, which supports rapid biomass turnover and continuous sediment carbon burial.
Distinctive variations emerge when examining seagrass genera and their geographical distribution. Meadows comprised of persistent genera such as Posidonia in the Mediterranean accumulate higher long-term carbon stocks within their biomass, reflecting slower growth yet greater longevity. Conversely, meadows dominated by opportunistic or colonizing species exhibit rapid growth rates and enhanced annual carbon capture but lower structural carbon accumulation. Regional disparities are also evident. Mediterranean meadows are characterized by substantial carbon deposits in sediments but moderate yearly growth, whereas North Pacific and temperate Atlantic meadows, although composed of shorter-lived plants, demonstrate faster growth rates and higher annual CO₂ absorption. Thus, some meadows optimize long-term carbon storage, while others excel at rapid carbon fixation, together contributing to a dynamic and complex global carbon cycle.
Despite their vital ecological role, seagrass meadows face relentless threats. Anthropogenic pressures such as coastal urbanization, nutrient pollution, and increasing sea temperatures owing to global warming have precipitated ongoing declines in these habitats. The resulting degradation not only diminishes biodiversity and coastal protection but triggers the release of stored carbon back into the atmosphere, exacerbating climate change. Current estimates attribute annual CO₂ equivalent emissions from seagrass biomass loss alone to between 154 and 256 gigagrams. Notably, five countries — Australia, Spain, Mexico, Italy, and the United States — collectively account for over 80% of these emissions, underscoring the urgent need for conservation efforts within these regions.
This new scientific quantification elevates seagrass meadows to the forefront of nature-based climate solutions, presenting opportunities for their inclusion in emerging blue carbon markets. Traditionally, carbon credit schemes have focused primarily on terrestrial and other coastal ecosystems like forests, mangroves, and saltmarshes. The validation of seagrass meadows as significant carbon sinks paves the way for their integration into such markets, potentially driving funding and incentives for their protection and restoration. Such economic mechanisms could provide vital resources to scale habitat recovery, ensuring that these underwater forests continue to safeguard carbon stocks and support marine biodiversity.
Lead author Enric Gomis emphasizes the multifaceted benefits of conserving seagrass meadows, stating that their protection not only contributes directly to CO₂ sequestration but also preserves rich biodiversity hotspots, enhances water quality, and stabilizes coastlines against erosion. The global balance established by this study fundamentally improves our understanding of seagrass ecosystems’ planetary significance, thereby enabling targeted global conservation policies. Òscar Serrano, the coordinating researcher from CEAB-CSIC, highlights that protecting seagrass meadows constitutes a natural, cost-effective climate mitigation strategy that holds immense promise in the urgent quest to limit greenhouse gas emissions and combat climate change impacts.
Ultimately, this landmark study challenges policymakers, conservationists, and society at large to recognize seagrass meadows not merely as hidden underwater landscapes but as powerful ecological allies. As the climate crisis accelerates, safeguarding these underwater forests presents a feasible and scalable approach to sustaining the ocean’s carbon sink capacity while fostering resilient marine ecosystems. With their extraordinary carbon storage potential and critical ecosystem services, seagrass meadows stand as a testament to nature’s ingenuity and a beacon of hope in the global fight to stabilize the climate.
Subject of Research: Not applicable
Article Title: Global estimates of seagrass blue carbon stocks in biomass and net primary production
News Publication Date: 3-Nov-2025
Web References: http://dx.doi.org/10.1038/s41467-025-64667-6
References: Gomis, E., Strydom, S., Foster, N.R. et al. Global estimates of seagrass blue carbon stocks in biomass and net primary production. Nat Commun 16, 9530 (2025).
Image Credits: CEAB-CSIC
Keywords: Oceanography
