The planet's areas covered by the sea, mangroves, marshes, and seagrass not only host a huge diversity of species, but, like the earth's vegetation, they naturally and durably capture and store carbon dioxide. The carbon stored by this aquatic vegetation is known as blue carbon, while what is known as green carbon is that which is captured by land plants.
Photosynthesis is, in essence, the base. Plants and marine organisms absorb carbon dioxide from both water and the atmosphere and convert it into biomass through biological processes. This carbon becomes part of its tissue, and, over time, a part is deposited in the seabed. When buried in sediments, where the shortage of oxygen causes it to decompose much more slowly than on the Earth's surface, carbon remains immobilized for decades, or even centuries.
As Emily Pidgeon, senior director of Strategic Marine Initiatives at The Blue Carbon Initiative, explains, "unlike other natural environments, low oxygen conditions in the soil of these systems allow them to retain carbon for centuries to millennia, as long as the ecosystems are maintained in good condition of conservation, which makes them carbon deposits of enormous global value."
A whole world in each ecosystem
Each coastal ecosystem acts differently. In mangroves, for example, complex aerial root networks and flooded soil act as natural carbon traps while protecting the coasts from erosion and serving as a refuge for numerous species.
The marshes combine halophytic vegetation (that is found in environments with high salt levels) and nutrient-rich sediments, favoring high carbon storage capacity and great biological productivity.
In the case of seagrass meadows, those of Posidonia in the Mediterranean, for example, are true "guardians of carbon", as they can capture between 33 and 426 grams of carbon per square meter per year. In comparison, tropical forests, such as the Amazon rainforest, sequester between 200 and 300 grams of carbon per square meter per year, but much of that carbon is released more quickly, especially if the forests are cut down or degraded.
Initiatives around the planet
In recent years, initiatives have been launched that demonstrate how the active conservation of blue carbon and the restoration of these ecosystems can provide tangible results.
A recent example is the seagrass meadow restoration project promoted by Fundación Moeve, together with the City Council of La Línea de la Concepción and the University of Cadiz. This initiative aims to recover key species such as Posidonia oceanica and other marine angiosperms on Poniente beach, where populations existed decades ago.
The project includes the production of plants and seeds in marshes during winter to initiate the restoration in spring 2026 using innovative techniques that increase the success rate and reduce costs. Thus, in addition to reinforcing biodiversity and protecting the coast against erosion, these meadows act as natural blue carbon sinks.
At an international level, initiatives such as the Vida Manglar Carbon Project, driven by Conservation International in the Colombian Caribbean, have demonstrated that mangrove restoration can generate a significant positive impact on the environment.
In Asia, the Singapore-based International Blue Carbon Institute has been established to support the protection and restoration of blue carbon coastal ecosystems in Southeast Asia and the Pacific, regions with a vast expanse of mangroves and seagrasses.
These projects combine science, conservation, and collaboration with the aim of strengthening the protection of ecosystems and improving their ability to store carbon naturally.
