Two decades of seagrass area change: Organic carbon sources and stock

Highlights: • Multidisciplinary approach provides clarification of historical seagrass change [83]. • Anthropogenic activities in coastal areas can directly influence seagrass meadows [84]. • Long term monitoring reveals highly dynamic and persistent seagrass areas [76]. • Two-decadal changes are valuable for proper management and conservation strategy [83]. Although seagrass ecosystems provide various ecosystem services, the implications in correspondence with temporal changes of the meadows is lacking. In this study, we analyzed two-decade changes of the seagrass area with the organic carbon storage and the sources at Libong island in Thailand. The seagrass area covered 841 ha in 2019, after two decades of decline (3.2 and 0.6% yr⁻¹ between 2004 and 2009 and 2009–2019, respectively). Although δ¹³C was not significant between depth layers (p > 0.05), the general trend suggested that the terrestrial source of carbon is dominating bottom depth layer (31.7–37.2%), mixture of terrestrial (19.7–30.3%), seagrass (22.9–29.6%), mangrove (16.8–43.0%) and CPOM (11.2–25.4%) in the middle, and mangroves and seagrasses are dominating surface layer (28.3–66.2 and 29.3–36.5%, respectively). These trends approximately correspond to the areal changes of the meadows, as well as changes of urban area and water quality, providing detailed information on the meadow changes and possible causes.