Seagrasses are an important blue carbon sink, due to their ability to sequester and store high amount of organic carbon, particularly in the sediment. Sedimentary organic carbon in seagrass meadows is derived from autochthonous production and allochthonous inputs from surrounding areas. Identification of organic carbon sources in seagrass sediments is necessary for evaluating the effectiveness of blue carbon sink. However, the distribution and accumulation of organic carbon vary geographically, and the lack of knowledge regarding the factors regulating this variability among seagrass meadows may lead to large uncertainties in the global carbon budget. This gap may limit the capacity to formulate strategies in climate change mitigation based on the carbon sink capacity of seagrass meadows. Therefore, in this study we identified the sources of sedimentary organic carbon in seagrass ecosystems from the Spermonde Archipelago, Indonesia. We measured Corg and N contents, and δ13Corg in seagrass sediments, and used the Bayesian Stable Isotope Mixing Model to analyze sources contribution to seagrass carbon stocks. In the areas where seagrass meadows are protected from the waves, seagrass contributed around 83 - 93 % to sediment carbon despite