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...