Intertidal coastal ecosystems (i.e. mudflats, salt marshes, seagrass beds, etc.) are present all over the world; they are often neglected in the global carbon budget, while these ecosystems are increasingly recognized to be as productive as tropical forests. Despite their potentially high contribution to the overall carbon budget, their actual contribution remains unknown. Moreover, these ecosystems are currently under threat from global changes and human activities. In this context, estimating the actual carbon uptake by these ecosystems is a challenge that has to be tackled, which is the objective of this project. Its main innovation resides in coupling remote-sensing, an expertise of the University of Nantes, with CO2 fluxes measured by atmospheric eddy covariance, an expertise of UC Berkeley, to map at the ecosystem level the gross primary production (GPP), corresponding to the carbon uptake by vegetation. This project will allow to estimate for the first time the contribution of theses ecosystems to the global carbon cycle. Prediction of ecosystem dysfunction consequences will be then possible, with the aim to develop mitigation and adaptation strategies to stand up global changes and support humanity to reach the objectives of the Paris Agreement.