Net cage aquaculture alters the co-occurrence network and functions of bacterial communities in offshore areas.

A better understanding of bacterial communities and the factors that drive them is essential to maintain their functions and services. As an ecosystem closely linked to human activities, the health of offshore aquaculture depends on the diversity and functions of bacteria in its environment. However, little attention has been paid to the vertical interface of the offshore aquaculture areas with shellfish net cages. In this study, high-throughput sequencing was used to analyze bacterial communities in different water layers of a net cage scallop farm in the offshore area of Northeast of China. Based on the results, an increased richness of bacterial communities was observed in the water adjacent to the net cages. Meanwhile, apparently different bacterial community compositions were observed among the water layers, with an enrichment of Cyanobacteria, Bacteroidota, and Firmicutes in the water layers above, parallel to, and below the net cages, respectively. According to the predicted functions, the bacterial communities of the water layers above, parallel to, and below the net cages were identified as phototrophy-, chemoheterotrophy-, and nitrogen respiration-dominated. Furthermore, network analysis revealed a complex but unstable bacterial community in the water layer containing the net cage. Finally, partial least squares path modelling revealed that the net cage aquaculture directly influenced the environmental variables and bacterial richness, which further induced the variations in bacterial community composition, and ultimately affected their ecological functions. These results provide a basic understanding of bacterial communities in net cage scallop farms and highlight the effects of offshore aquaculture on variations in ecological functions.