Temporal–Spatial Variations in Microbial Diversity and Community Composition in Surface Waters and Bottom Sediments of the Bohai Sea, China

Temporal variation in microbial communities is critical for sustainable utilization of marine biological resources and ecological restoration. However, microbial communities in China’s Bohai Sea remain inadequately characterized. This study employed high-throughput sequencing to characterize temporal–spatial variations in microbial communities within surface water and bottom sediment between June and August. A distinct temporal zone emerged in the sediments in August, characterized by low dissolved oxygen, bottom water acidification, and elevated concentrations of TN, NO3−, PO43−, and DOC. Furthermore, temporal variation exerted a stronger influence on microbial community. August induced a significant decline in aerobic bacteria and an increase in anaerobes. Crucially, a substantial increase in ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), coupled with a decrease in denitrifying bacteria, likely contributed to observed NO3− accumulation. Furthermore, complex alterations in sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) populations suggested potential impacts on sulfur cycling. This study provides critical insights for temporal–spatial variations in the microbial communities of the Bohai Sea, and provides a reference for developing effective coastal health indicators and further microbe resource exploration.