Community Structure of Labyrinthulomycetes Protists in <i>Zostera marina</i> Seagrass Beds of Northern China

Labyrinthulomycetes protists play important roles in organic matter decomposition and nutrient cycling in marine ecosystems. To better understand their distribution and potential ecological functions in Caofeidian seagrass beds of the Bohai Sea, we conducted high-throughput sequencing of samples collected from multiple habitats, including leaves (L), rhizosphere (R), sediments (S), and seawater (W). Our results revealed distinct habitat-specific patterns of community composition. <i>Oblongichytrium</i> and <i>Stellarchytrium</i> were dominant in certain samples, exhibiting clear differences across stations. <i>Oblongichytrium</i> showed particularly high abundance in leaf and seawater samples, likely reflecting the availability of particulate and dissolved substrates enriched by seagrass beds. In the rhizosphere, <i>Sicyoidochytrium</i>, <i>Stellarchytrium</i> and <i>Labyrinthula</i> were enriched, whereas unclassified Labyrinthulomycetes and Thraustochytriaceae lineages prevailed in seawater and specific leaf samples. Notably, a substantial proportion of sequences corresponded to unclassified lineages, potentially representing uncultured “seagrass-associated” taxa. Compared with previous reports, our study revealed both a significantly higher abundance of <i>Stellarchytrium</i> and a remarkably greater proportion of unclassified lineages, suggesting unique features of Labyrinthulomycetes communities in the Caofeidian seagrass ecosystem. These findings provide new insights into the ecological roles of Labyrinthulomycetes in seagrass beds and offer an important reference for future taxonomic and functional studies of this group.