Newly discovered seagrass beds and their potential for blue carbon in the coastal seas of Hainan Island, South China Sea

Eight new seagrass beds were discovered along the coastline of Hainan Island in South China Sea with an area of 203.64 ha. The leaf N content of all seagrasses was above the median value, indicative of N limitation, with their C:N ratio recorded significantly lower than the limiting criteria. This suggested that N is not limiting but in replete status. Further, the lower C content observed in the seagrass leaves was accompanied by higher nutrient concentration. The mean seagrass biomass C was 0.23 ± 0.16 Mg C ha− 1, while the average sediment organic carbon (SOC) stock was 7.02 ± 3.57 Mg C ha− 1. The entire SOC stock of the newly discovered seagrass beds was 1306.45 Mg C, and the overall SOC stock of seagrass bed at Hainan Island was 40858.5 Mg C. These seagrass beds are under constant threats from sea reclamation, nutrient input, aquaculture activities for oyster and snail farming, and fishing activities.