Microorganisms in sediments participate actively in biogeochemical cycling and are essential for maintaining the stability of marine ecosystems. To investigate the spatial impact of seaweed mariculture on sediment bacterial communities, three distinct zones were selected along the Zhanjiang coast, China: the Gracilaria salicornia aquaculture zone, a transition zone (adjacent to the aquaculture area), and a control zone (with no direct mariculture influence). In this study, 16S rRNA gene amplicon sequencing was employed to examine the composition, diversity, and potential functions of sediment bacterial communities across these three zones. The dominant microbial communities identified included Pseudomonadota, Thermodesulfobacteriota, Chloroflexota, and Acidobacteriota. Analyses of α-diversity, β-diversity, and molecular ecological network revealed that the bacterial community in the G. salicornia aquaculture zone exhibited significant differences in species composition, community structure, and interspecies interaction compared with those in the transition and control zones. Environmental factors such as pH, dissolved oxygen (DO) and nitrate (NO₃⁻) exerted significant influence on the bacterial community composition and structure. Predicted functional potential analyses indicated high abundances of pathways related to carbohydrate metabolism and amino acid metabolism. Overall, this study characterizes the spatial distribution patterns of microbial communities in a coastal seaweed mariculture ecosystem and provides important data to support further research on biogeochemical processes mediated by sediment bacteria and their response mechanisms to mariculture activities.