Mangrove Habitat Health Assessment in the Sanya River: Multidimensional Analysis of Diatom Communities and Physicochemical Water Properties

Mangrove forests are vital ecosystems along tropical coasts, playing crucial roles in water purification and biodiversity conservation. Diatoms, as sensitive ecological indicators, were employed in this study to evaluate the health of the mangrove forests along the Sanya River. The research involved analyzing the community structure of planktonic diatoms and water physicochemical properties during spring and winter, as well as carrying out a comprehensive assessment of the ecological health of the region in terms of four seasonal&ndash:spatial&ndash:environmental&ndash:biological indices. A total of 22 genera of planktonic diatoms were identified. In winter, Melosira sp. (34.94%), Skeletonema sp. (25.50%), and Chaetoceros sp. (15%) were dominant, with relative abundances of 34.94%, 25.50%, and 15.00%. In spring, Melosira sp. became the absolutely dominant species, averaging 70.16%. Diatom cell abundance shows both significant seasonal and spatial variation. In winter, it ranged from 0.53 to 17.4 &times: 109 cells-L&minus:1, peaking in the midstream region, whereas in spring, it ranged from 2.48 to 21.0 &times: 109 cells-L&minus:1, peaking at the mouth of the estuary. A higher abundance of diatoms in spring strengthens primary productivity and supports the subsequent functioning of the food chain. Diatom indices (Shannon&ndash:Wiener index H&rsquo:, Pielou evenness index J, and Margalef richness index D) indicated an intermediate ecological health level for the Sanya River mangrove forests. Diversity was higher in winter than in spring, with the lowest values recorded in the midstream region. Redundancy analysis (RDA) indicated that T, pH, and PO43&minus: were the primary environmental drivers of diatom community succession. In spring, pH was positively correlated with T and PO43&minus:, respectively. They drove the succession of diatom communities from diverse assemblages in winter to a single dominant species.