Environmental Determinants of the Distribution of Halophila beccarii Ascherson in Hainan Island, China

This study presents the first record of the overall distribution of the seagrass Halophila beccarii Ascherson on the island of Hainan. Statistical and ecological methods were used to analyze the distribution of the species and the influence of environmental factors. Halophila beccarii was mainly distributed in the northwest and southeast of Hainan, in lagoons with a total area of 20.981 km2, including the largest H. beccarii area in China covering approximately 9.58 km2 in Xiaohai, Wanning; there were also 4.89 km2 in Xinying Bay, Danzhou, approximately 2.20 km2 in Huachang Bay, Chengmai, 1.88 km2 in Dongzhai Port, Haikou, 0.95 km2 in Xinying Port, Lingao, approximately 0.668 km2 in Laoyehai, Wanning, approximately 0.363 km2 in Hongpai, approximately 0.23 km2 in Maniao, and approximately 0.22 km2 in Huanglong Port, Lingao. The average coverage of H. beccarii measured at 7.08–56.33%, the density of stem and branch was 487.47–20,167.1 ind/m2, and the biomass measured at 1.57–112.94 gDW/m2. The growth distribution was mainly influenced by habitat type and, to a lesser extent, by tidal branching channels, heavy metal content (Cu, Pb, Cr, Zn) in the marine environment, and human activities in adjacent coastal areas.