Carbon sequestration in wetland dominated coastal systems - a global sink of rapidly diminishing magnitude

► Vegetated coastal systems, including seagrass beds, mangroves, and intertidal marshes currently sequester 67-215 Tg C yr−1, globally. ► There is considerable uncertainty in the magnitude of C storage because of the difficulty in extrapolating rates with very high spatial variability and we lack accurate and precise measures of the coverage of these systems in many parts of the world. ► The magnitude of C sequestration by these systems is declining and will continue to decline primarily because of direct human conversion of these systems to other uses and anthropogenic activities that affect global climate and the quality of river runoff. ► A decline in rates of C sequestration by vegetated coastal systems over time will contribute to ever increasing levels of CO2 in the atmosphere and hence climate change.