Assessing macroalgae composition in surface sediments of the Ma'an Archipelago seaweed field based on eDNA technology

Macroalgae contribute to the seafloor sediments as detritus when they die or detach. Tracking the distribution of macroalgae is crucial to understanding their contribution to seafloor sediments. To assess species composition and distribution of macroalgae in sediments, we used environmental DNA (eDNA) technology to analyze surface sediments from four typical island waters, including Ma'an Archipelago Special Marine Protected Area, eas-tern Lyuhua (DLH), western Lyuhua (XLH), Mantou Mountain (MTS), and Mandui Mountain (MDS). A total of 18 orders of macroalgae were recorded in the sediment samples, including 13 orders, 21 families, and 23 genera of red algae species and 5 orders, 5 families, and 5 genera of brown algae species. At the family level, Corallinaceae, Hapalidiaceae, Dictyotaceae, and Sargassaceae were the dominant ones. The number of OTU sequences of macroalgae accounted for 37.2% of the total in the sediment samples. Results of non-metric multidimensional sca-ling sorting (NMDS) and analysis of similarity (ANOSIM) showed that the composition of macroalgae was consis-tent across different areas. The results indicated that red algae were the dominant algae in the sediments, consistent with the distribution characteristics of seaweeds. eDNA technology was feasible for analyzing the composition of macroalgae in sediments, providing valuable data for monitoring macroalgal diversity and supporting the ecological ma-nagement of seaweed farm protection.