The Microbiology and Geochemistry of the Shallow‐Water Hydrothermal Vents of the Gulf of Naples, Italy

Shallow-water hydrothermal vents are dynamic ecosystems that occur below 200 m in tectonically active regions of the planet. While their geochemical composition has been investigated in several locations, knowledge about the microbial diversity they harbour remains scarce. Moreover, the relationships between hydrothermal fluid chemistry, geological settings and microbial community structure in shallow vents have not been explored in detail. Here, we investigate the interplay between fluid geochemistry and microbial diversity in two underwater volcanic regions in the Gulf of Naples, Italy, one under the influence of the Somma-Vesuvio volcano and the other located within the underwater portion of the Campi Flegrei caldera. By combining 16S rRNA amplicon sequencing with geochemical measurements, and by contextualising it with previous geochemical measurements done in the region, we found that hydrothermal fluid chemistry, influenced by the geological setting where the vents are hosted, plays a key role in shaping microbial ecological niches and imposes strong selective pressures on the resident microbial communities. We additionally describe two new shallow vent sites, contributing to the characterisation of the hydrothermalism in the area and unveiling the biodiversity associated with shallow-water hydrothermalism in the region.