Abstract: Enhalus acoroides is the dominant seagrass species in Xincun Bay and Li’an Harbor, Lingshui, Hainan, but has shown an obvious declining trend in recent years. From 2021 to 2022, we conducted investigations on the E. acoroides seagrass beds for six times in Xincun Bay and Li’an Harbor. We measured the morphological and physiological variables of E. acoroides, and analyzed the effects of environmental factors on those variables. The results showed that seawater temperature, pH, ammonium, DIN, phosphate, seagrass leaf length, belowground issue C/N ratio were significantly higher in Xincun Bay than in Li’an Port, while seawater salinity, nitrate concentration, leaf width and N content of belowground tissues were significantly lower in Xincun Bay than in Li’an Port. E. acoroides in Xincun Bay was mainly affected by seawater salinity, pH, and sediment grain size. Leaf length was positively correlated with seawater salinity, pH, and sediment grain size. Aboveground, belowground, and total biomass were positively correlated with sediment grain size and seawater salinity. In Li’an Port, E. acoroides was greatly affected by seawater salinity, pH, nitrate, phosphate, and sediment organic carbon. The aboveground, belowground, and total biomass were significantly negatively correlated with the sediment organic carbon and seawater ammonium, and positively correlated with seawater pH and nitrate. Compared with historical data, the nitrogen content in seagrass tissues significantly increased (>2.45%). In the future, the discharge of aquaculture sewage into the seagrass beds in Xincun Bay and Li’an Port should be strictly controlled. Special funds should be set up for long-term monitoring of the health status of seagrass beds, and research on the degradation mechanism of damaged seagrass beds should be strengthened. This study can provide a scientific basis for understanding the synergistic effects of seawater temperature, salinity, and nutrients on E. acoroides.

Key words: Enhalus acoroides, morphological indicator, physiological indicator, nutrient, environmental parameter