Seagrass blue carbon stocks and emission potential in the Derawan Islands Marine Protected Area, Indonesia

Blue carbon ecosystems, particularly seagrass meadows, are among the most efficient natural carbon sinks due to their capacity to sequester and store large quantities of organic carbon in long-lived marine sediments. This study quantified seagrass biomass and sediment carbon stocks, assessed spatial variability across management zones, and estimated potential carbon dioxide (CO₂) emissions associated with seagrass degradation in the Derawan Islands Marine Protected Area (DIMPA), East Kalimantan, Indonesia. Field surveys were conducted at six sampling stations representing two management categories: Coastal Park and Small Island Park. Seagrass cover, biomass, sediment carbon stocks, and environmental parameters were measured, while carbon emissions were estimated using an IPCC-consistent carbon-stock difference approach. Total ecosystem carbon stocks ranged from 153.88 to 244.06 t C ha⁻ 1 , with sediment carbon accounting for approximately 99% of total storage, highlighting the dominant contribution of belowground carbon pools. No significant differences in seagrass cover or carbon stocks were observed between management zones, indicating similar ecological pressures across the protected area. Comparison with a previous blue-carbon assessment conducted in 2014 using a comparable sediment-core methodology revealed a substantial decline in ecosystem carbon stocks by 2025, corresponding to an estimated reduction of approximately 36% in carbon-storage capacity. The estimated emission factor between 2014 and 2025 was 36.97 t CO₂ ha⁻ 1 yr⁻ 1 , highlighting the considerable climate-mitigation value at risk from continued seagrass degradation. These findings indicate that seagrass ecosystems within marine protected areas remain vulnerable to carbon loss and that spatial protection alone may be insufficient to safeguard blue carbon stocks. Strengthening management effectiveness and reducing pressures associated with coastal development, tourism activities, fishing pressure, pollution, land-use change, and land-based sediment and nutrient inputs are critical for maintaining seagrass carbon storage, reducing potential emissions, and sustaining ecosystem climate-regulation functions.