Background Certain coastal habitats such as marshes and seagrass meadows, including Neptune grass (Posidonia oceanica) meadows, are significant carbon sinks, both in terms of the intensity of gas sequestration and carbon deposits that are stored for thousands of years. Despite the importance of this, and other ecosystem services, these habitats are disappearing at a rate which is four times greater than terrestrial forests. Objectives The LIFE Blue Natura project’s main aim is to quantify the carbon deposits and the sequestration rates of marsh and seagrass meadow habitats in Andalusia. An emphasis will be placed on what is accumulated under the ground or sea, as well as analysing predicted future developments, from the carbon loss rate, to potential carbon fixation and accumulation rates, and the emission/sequestration ratio of carbon from damaged meadow zones into the atmosphere. This information will enable an approximate evaluation of the environmental services created by these habitats to be made. It should also encourage existing initiatives to finance conservation and restoration projects of blue carbon sink-habitats and the development of key policies for mitigating and adapting to climate change, with special attention to carbon emissions trading or carbon markets. Expected results: Project calculations of the carbon stocks and carbon flows for the Neptune grass (Posidonia oceanica) sink in Andalusia; and the carbon sink of other marsh and seagrass habitats in the Bay of Cadiz, the Strait, and the Odiel Marshes; Assessments of the environmental services provided by the above habitats, as carbon sinks in mitigating climate change and enabling the selection of pilot sites for the conservation and re-vegetation of the most valued/most threatened areas; Models built that allow for an essential description of these carbon sinks, which describe their capacity, time and maximum sequestration potential, or the net rate of CO2 release in the case of habitat destruction; Tools developed to facilitate the implementation of strategies for the conservation of these carbon sinks using regulated/voluntary carbon markets, such as the Andalusian verification standard of carbon credits, created for carbon offset projects based on the conservation of Neptune grass (Posidonia oceanica); and Encouraging dialogue at a national level about how blue carbon habitats can be incorporated into the national Inventory of greenhouse gases (GHGs), which will create a network of companies and organisations involved in the carbon trading market.