Mangrove forests have the potential to export carbon to adjacent ecosystems but whether mangrove-derived organic carbon (OC) would enhance the soil OC storage in seagrass meadows adjacent to mangroves is unclear. In this study we examine the potential for the contribution of mangrove OC to seagrass soils on the coast of North Sulawesi, Indonesia. We found that seagrass meadows adjacent to mangroves had significantly higher soil OC concentrations, soil OC with lower δ 13C, and lower bulk density than those at the non-mangrove adjacent meadows. Soil OC storage to 30 cm depth ranged from 3.21 to 6.82 kg C m−2, and was also significantly higher at the mangrove adjacent meadows than those non-adjacent meadows. δ13C analyses revealed that mangrove OC contributed 34 to 83% to soil OC at the mangrove adjacent meadows. The δ13C value of seagrass plants was also different between the seagrasses adjacent to mangroves and those which were not, with lower values measured at the seagrasses adjacent to mangroves. Moreover, we found significant spatial variation in both soil OC concentration and storage, with values decreasing toward sea, and the contribution of mangrove-derived carbon also reduced with distance from the forest.

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In 2006, the amounts of seagrass products floating away and depositing were measured by in situ cage experiments in a monospecific seagrass meadow of Enhalus acoroides in Gilimanuk Bay, Bali Island. Results showed that the average rates of the floating and depositing leaves were 4.03 + 0.28 and 7.95 + 0.31 gram dry weight shoot-1 day-1 respectively. To express it in another way, about 66.4 % of seagrass production was deposited on the seagrass bed and 33.6 % floated away from the seagrass bed.