Abstract
Environmental physicochemical factors and microorganisms play critical roles in the health of oysters. However, the impact of high-density oyster farming-a highly efficient filter-feeding bivalve system-on environmental conditions and microbial community structure and function remains poorly understood. This study conducted four-season monitoring of the water and sediment parameters in a semi-enclosed bay commercial oyster aquaculture (OA) system and a control area (CT), coupled with 16S rRNA amplicon sequencing of the environmental microbiota. Oyster aquaculture caused negligible disruption to water column parameters but significantly increased the concentrations of total organic carbon (TOC, annual mean OA vs. CT:1.15% vs. 0.56%), sulfides (annual mean OA vs. CT:67.72 vs. 24.99 mg·kg(-1)), and heavy metals (Cd, Pb, Cu, Zn, and Cr) in the sediment. α-diversity (Shannon and Chao indices) exhibited minimal overall perturbation, with significant inter-regional differences observed only in winter for both water and sediment. The bacterial community structure of the water column was significantly altered only in winter, whereas sediment communities showed structural shifts in spring, summer, and autumn. Water microbiota were primarily influenced by turbidity, dissolved oxygen, salinity, the Si/N ratio, and silicates. Sediment microbiota were correlated with Pb, Cu, Zn, TOC, Cr, and sediment particle size. Water bacterial functions displayed only four significantly divergent biogeochemical processes annually (sulfur compound respiration; OA vs. CT). In contrast, sediment bacteria exhibited 29 significantly disrupted functions annually, with the greatest seasonal divergence in winter (11/67 functions). Spring, summer, and autumn sediment functions showed distinct patterns. Understanding these environmental-microbial interactions is essential for sustainable oyster aquaculture and ecological optimization.