Spatial distribution of benthic microbial assemblages in a coastal upwelling ecosystem off Atacama Desert (23° S), northern Chile. Spatial distribution of benthic microbial assemblages in a coastal upwelling ecosystem off Atacama Desert (23° S), northern Chile

Coastal marine sediments are highly dynamic and subject to periodic organic substrate additions that favor an anoxic sediment-water interface. Mejillones Bay located in the Humboldt Current is a highly productive system subject to the presence of shallow oxygen minimum zones (OMZs) leading, in turn to sea bottom’s persistent hypoxic conditions. Although it is often considered a hotspot of microbes involved in the nitrogen cycle, the diversity and microbial distribution from sediments in this environment remain poorly researched. To elucidate how the hypoxic conditions, together with the effect of the heavy metal concentrations and organic matter can alter the spatial distribution of benthic microbial communities within the Bay, we analyzed the microbial community structure of surficial sediments by Illumina-sequencing of the 16S rRNA gene at two localities within the bay (Punta Rieles and Punta Chacaya), along water-depth from 10 to 50 m. As well as physicochemical variables that describe the environmental conditions of the water column and sediment features were measured. Here found that Proteobacteria (mainly δ-Proteobacteria, γ-Proteobacteria and α-Proteobacteria) formed the most abundant and diverse group, followed by Actinobacteria, Bacteroidetes, Chloroflexi, Acidobacteria and Planctomycetes. ASVs richness and diversity were common to both sampling localities, but they are significantly different along the water-depth gradients. Redundancy analyses showed that the environmental variables including the metals were effectors that propelled the differentiation of sedimentary community structure. Co-occurrence network constructed indicated that microbial community composition was conformed by groups specialists of the organic matter decomposition relate in turn to sulfur‐oxidizing in sediments influenced by water-column hypoxic conditions, supporting the hypothesis that anaerobic lifestyles seem to be favored in sediments of the Mejillones Bay. Therefore, we postulate that these taxa may a significant influence on environmental stability and your loss could affect negatively influence the nitrogen and sulfur cycles in the Bay.