| Summary: | Seagrasses demonstrate complex ecological functions, and their morphological and physiological indicators are affected by various environmental factors. In this study, we conducted six sampling surveys of a Thalassia hemprichii seagrass bed in Xincun Bay, Lingshui, Hainan in 2019. The morphological and physiological characteristics of seagrasses in January, March, May, July, September, and November of a single year were studied, and the effects of various environmental factors on the morphological and physiological characteristics of T. hemprichii were analyzed. The results demonstrated markedly differences in leaf length and width, rhizome length and thickness, and root length across different months. The highest value [(15.05±6.13) cm] of leaf length occurred in May, and the lowest value [(7.19±2.55) cm] in September. The highest [(11.93±1.68) mm] and the lowest [(8.73±1.96) mm] values for leaf width were recorded in November and September, respectively. The highest value [(5.22± 1.71) mm] for rhizome diameter occurred in November, and the lowest value [(4.06±0.74) mm] in March. The C content of the underground seagrass tissues was significantly different across months, with the highest value (31.23%±0.94%) in November and the lowest value (24.90%±3.48%) in March. Seawater temperature had a significantly positive correlation with leaf width and C content of the underground tissues. Salinity was significantly positively correlated with the leaf and rhizome lengths of T. hemprichii and had a negative relationship with the C content of the underground tissues. There was a significant positive correlation between pH and leaf length, leaf width, and C and N content of the underground tissues. The ammonium level in seawater was significantly positively correlated with the N content of aboveground tissues. Nitrate level of seawater was negatively correlated with the C/N ratio of the aboveground parts. There was a significant positive correlation between the dissolved inorganic nitrogen (DIN) in seawater and the N content of the underground parts. Sediment organic carbon had a negative relationship with leaf length and width, and rhizome growth. The results demonstrated that the growth of T. hemprichii in Xincun Bay was greatly affected by temperature, salinity, and pH. A high nutrient level in Xincun Bay may have a negative impact on T. hemprichii. In order to protect the T. hemprichii meadow, measures should be taken to limit the input of nutrients in Xincun Bay. The results of this study may provide data support and serve as a scientific basis for the restoration of declining seagrass.
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