Proteobacteria Dominance and Neutral Assembly Processes of Bacterial Communities in the Chukchi Sea, Arctic

Abstract. Bacteria play a vital role in maintaining ecosystem functioning under rapidly changing environmental conditions, however, the characteristics and assembly mechanisms of bacterial communities at regional scales in the marine ecosystem of the Arctic Chukchi Sea remain poorly understood. Using 16S rRNA gene amplicon sequencing, we investigated the composition, diversity, and assembly processes of bacterial communities across three distinct water layers (Surface, Middle, and Bottom) in the Chukchi Sea. The results revealed a significant increase in community richness in the Middle and Bottom layers compared to the Surface layer, with Alphaproteobacteria, Cyanobacteriia, and Bacteroidia as the predominant classes. The bacterial community structures differed significantly across the water layers, and their β-diversity was primarily driven by species turnover. Environmental variables explained approximately 48.2 % of the variation in community structure, with water depth, dissolved oxygen (DO) and silicate were identified as driving factors (p<0.05). Furthermore, network analysis indicated that the bacterial co-occurrence network in the middle layer exhibited greater complexity and stability. The Neutral community model (which explained 61.9 % of community variation) and null model analyses collectively demonstrated that while both deterministic and stochastic processes govern bacterial community assembly in the Chukchi Sea, stochasticity is the dominant force. These findings advance our understanding of depth-stratified bacterial ecology in the Chukchi Sea and provide a crucial foundation for future studies on ecosystem responses to ongoing environmental changes in the Arctic.