Indonesia’s blue carbon: a globally significant and vulnerable sink for seagrass and mangrove carbon

The global significance of carbon storage in Indonesia’s coastal wetlands was assessed based on published and unpublished measurements of the organic carbon content of living seagrassand mangrovebiomass and soil pools. For seagrasses, medianabove- and below-ground biomass was 0.29 and 1.13 Mg C ha−1 respectively; the mediansoil pool was 118.1 Mg C ha−1. Combining plant biomass and soil, mediancarbon storage in an Indonesian seagrassmeadow is 119.5 Mg C ha−1. Extrapolated to the estimated total seagrassarea of 30,000 km2, the national storage value is 368.5 Tg C. For mangroves, medianabove- and below-ground biomass was 159.1 and 16.7 Mg C ha−1, respectively; the mediansoil pool was 774.7 Mg C ha−1. The mediancarbon storage in an Indonesian mangroveforest is 950.5 Mg C ha−1. Extrapolated to the total estimated mangrovearea of 31,894 km2, the national storage value is 3.0 Pg C, a likely underestimate if these habitats sequester carbon at soil depths >1 m and/or sequester inorganic carbon. Together, Indonesia’s seagrassesand mangrovesconservatively account for 3.4 Pg C, roughly 17 % of the world’s blue carbonreservoir. Continued degradation and destruction of these wetlands has important consequences for CO2 emissions and dissolved carbon exchange with adjacent coastal waters. We estimate that roughly 29,040 Gg CO2 (eq.) is returned annually to the atmosphere–ocean pool. This amount is equivalent to about 3.2 % of Indonesia’s annual emissions associated with forest and peat land conversion. These results highlight the urgent need for blue carbonand REDD+ projects as a means to stem the decline in wetland area and to mitigate the release of a significant fraction of the world’s coastal carbon stores.