Abstract: This study systematically investigated two typical seagrass beds in Guangdong Province—a lagoon-type bed in Zhanjiang Liusha Bay and an estuarine-type bed in Shantou Hanjiang Estuary—to clarify their community structure characteristics, identify key environmental factors, and evaluate ecosystem health. The results showed that all seagrass species identified belong to the genus Halophila. The Liusha Bay seagrass bed was composed of Halophila ovalis and H. minor, with H. ovalis as the dominant species, while only H. beccarii was recorded in the Hanjiang Estuary. Although seagrass coverage was higher in Liusha Bay (57.33%) than in the Hanjiang Estuary (34.22%), there was no significant difference in coverage or shoot density between the two sites. However, total biomass (27.36 g/m²) and mean shoot height (2.41 cm) in Liusha Bay were significantly greater than those in the Hanjiang Estuary (8.07 g/m² and 1.88 cm, respectively) (P < 0.05). Correlation analysis indicated that the key environmental drivers differed between the two sites: in Liusha Bay, seagrass community structure showed significant positive correlations with shoot density, light transmittance, and inorganic nitrogen (P < 0.05), whereas in the Hanjiang Estuary, it was significantly negatively correlated with sulfide and salinity (P < 0.05). Ecosystem health assessment revealed that both seagrass beds were in a sub-healthy state. Liusha Bay exhibited sub-healthy conditions in water quality, habitat, and biological indicators, but its sediment environment and biological quality were relatively better, with main pressures coming from eutrophication and habitat degradation. In contrast, the Hanjiang Estuary showed sub-healthy conditions across water quality, habitat, and biological indicators, with more pronounced eutrophication, less stable substrate, and greater decline in biological indicators. This study systematically compared the ecological characteristics and health status of lagoon-type and estuarine seagrass beds, revealing significant differences in community structure, environmental influencing factors and health stressors between the seagrass beds in these two habitat types. It highlights the necessity of classified conservation and precision restoration and provides a scientific basis and targeted reference for the ecological conservation and restoration practices of in typical lagoonal and estuarine type seagrass bed ecosystems.

Key words: seagrass bed, lagoon-type and estuarine-types, community structure characteristics, environmental factors, ecosystem health assessment