Characterization of surface microbial communities on four seaweed species from the East China Sea

Sargassum thunbergii (ST), Sargassum horneri (SH), Grateloupia livida (GI), and Ulva pertusa (UP) are common seaweed in the East China Sea. This study investigated the epiphytic microbial communities associated with these four seaweeds in the intertidal zone of Gouqi Island, using natural seawater (SW) and sediment (S) as controls. High-throughput sequencing of 16S rRNA gene amplicons was employed to compare the community structures. The results indicated that ST exhibited lower microbial diversity and species richness compared to the other three seaweeds. Non-metric multidimensional scaling (NMDS) and principal coordinate analysis (PCoA) revealed significant differences in the community structures of epiphytic microbiota on the four seaweeds compared to those in seawater (P < 0.05). The microbial community of ST was significantly distinct from those of the other three seaweeds (P < 0.05), while no significant differences were observed among UP, GI, and SH. LEfSe analysis identified 24 biomarkers, distributed as follows: 18 for SW, 4 for ST, 1 for UP, 3 for S, 1 for GI, and 3 for SH. The dominant bacterial phyla in the epiphytic microbial communities of the four seaweeds were Proteobacteria, Firmicutes, and Bacteroidota, with relative abundances ranging from 84.35 % to 94.98 %. At the genus level, the top 10 taxa in relative abundance exhibited distinct compositional differences among the four seaweeds, demonstrating host specificity. Ecological functional predictions using FAPROTAX indicated that the epiphytic microbial communities were associated with metabolic processes such as nitrogen respiration, nitrate respiration, sulfur compound respiration, and oil bioremediation. By comparing the diversity and structural characteristics of epiphytic microbial communities on the four seaweeds, this study provides a theoretical basis for further understanding the ecological roles of seaweed.