Drift, dispersal limitation, and homogeneous selection as key processes shaping prokaryotic community assembly in marine sediments

Marine sediment contains some of the most abundant and diverse microbial communities; however, the ecological processes shaping the benthic microbial communities at the regional scale remains poorly understood. Using a high-coverage sampling strategy, 16S rRNA gene sequencing, and ecological null models, we explored variation in the ecological processes governing benthic microbial community assembly in surface sediments across an extensive Southwest Atlantic basin. The relative importance of ecological processes varied between provinces, with drift, dispersal limitation, and homogeneous selection being the three main processes that shaped the communities. Phylogenetic bin-based analysis revealed a complex balance of assembly mechanisms, with drift dominating the majority of the bin assembly of the dominant groups such as <i>Candidatus</i> Nitrosopumilus, <i>Pirellula</i>-like planctomycetes, and <i>Woeseia</i>. The environmental factors driving this processes were associated with sediment characteristics and organic matter quality, although they differed among provinces. Drift emerged as the dominant process, influenced by sediment grain size and depth in deeper regions and organic matter properties on the continental shelf. Dispersal limitation was linked to sediment and bottom water properties, while homogeneous selection was associated with sediment aluminum and hydrocarbon content. These findings highlight the role of spatial variation and environmental factors in benthic microbial community assembly at a regional scale, providing a framework for understanding microbial community assembly in oceanic basins, and emphasizing the need for province-specific management strategies.