Mangrove could be a potential exporter of organic carbon to its adjacent costal ecosystems.However, the ecological information on the carbon exchange across the coastal systems is still limited.In this study, the soil carbon storages and their sources were compared between the mangrove-fringed and non-mangrove-fringed seagrass meadows in North Sulawesi, Indonesia, to test if mangrove-derived carbon contributes to the carbon storage in its fringed seagrass meadow, and the spatial variation in carbon storage with distance off-shore was also investigated.The mangrove-fringed seagrass meadows tended to be richer in soil organic carbon, which was dominated by the mangrove-derived carbon based on a multiple δ13C analysis.However, due to the low soil bulk density in mangrove-fringed meadow, the difference in soil carbon storage was less significant between the two seagrass habitats, compared to their soil OC content.Significantly spatial variation in both soil OC and carbon storage were found in the seagrass meadows, with values decreasing with distance toward the sea.The contribution of mangrove derived carbon also faded with distance from the forest.Nevertheless, seagrass represented only a small fraction of the soil organic carbon, irrespectively the occurrence of mangrove forest in this study, and more depleted δ13C was measured in the seagrass adjacent to mangrove forest.The results further suggest that seagrass meadows could limit the export of both mangrove-derived organic and inorganic carbon toward the coastal ocean.