National assessment and variability of blue carbon in seagrass ecosystems in Thailand

Seagrass ecosystems are important organic carbon (C_org) sinks with great potential to contribute to climate change mitigation strategies. However, the high spatial and temporal variability is a barrier to the accurate assessment of national C_org stocks. This study provides a national assessment of C_org within seagrass meadows, including spatial and temporal variations. The highest C_org stocks were within mangrove-associated (44.3 ± 8.27 Mg ha^-1), while near-surface sediments were highest in reef-associated meadows (10.20 ± 3.69 Mg ha^-1). Regionally, the highest stocks were in the Upper Andaman coast in monospecific meadows (51.7 ± 7.14 Mg ha^-1). C_org stocks in near-surface sediments were significantly different across historical trends (p < 0.001), with the highest stocks in stable meadows (9.28 ± 3.39 Mg ha^-1). The national C_org stock within seagrass meadows sediment was 40.45 ± 11.59 Mg C ha^-1. The results of this study highlighted the complexity of blue carbon in seagrass meadows and the associated impacts on national C_org assessments, carbon accounting, and conservation strategies.