Metabarcoding analysis of eukaryotic microalgae communities in the surface sediments of an integrated multi-trophic...

Coastal ecosystems are increasingly threatened by the synergistic pressures of intensive aquaculture and fluctuating terrestrial runoff, yet the mechanisms by which these drivers shape foundational benthic and pelagic algae remain poorly understood. To address this gap, this study systematically investigates the spatiotemporal dynamics of benthic and pelagic algae in Sungo Bay by integrating pigment fingerprinting with high-throughput sequencing. Results indicate that mariculture type is a primary determinant of community structure. Dinophyceae dominated coastal and kelp cultivation zones, while Trebouxiophyceae and Ulvophyceae prevailed in the oyster cultivation zone. Seasonal terrestrial fluxes further modulated these patterns, creating a pronounced winter-summer dichotomy. During winter, intensified oyster filtration and biodeposition, coupled with terrestrial inputs, elevated sedimentary total organic carbon/total nitrogen (TOC/TN) ratios (6.83-30). These elevated ratios correlated with enhanced photosynthetic pigment concentrations, increased sequencing reads, and higher operational taxonomic unit (OTU) richness, coinciding with the dominance of Trebouxiophyceae and Ulvophyceae. In summer, reduced oyster filtration shifted TOC/TN regulation to terrestrial inputs, driving a successional transition to Trebouxiophyceae dominance. This work elucidates the dual regulatory roles of aquaculture practices and seasonal terrestrial fluxes, providing critical insights for managing benthic-pelagic coupling and ecosystem function in anthropogenically influenced coastal zones.