taxonomic group or entity. This may be a family, class, genus, species, etc.; usually this parameter will contain a mixture of taxonomic entities.
Shallow-water hydrothermal vents are ubiquitous ecosystems distributed worldwide between the inter-tidal zone and ~ 200 m depth. Important factors differentiating shallow-water vents from their deep-sea counterparts include the presence of sunlight, tidal/wave forcing, meteoric water sources, terrigenous inputs of organic matter and abundant free gas. The presence of sunlight and high organic carbon loads together with differences in availability of electron donors and acceptors defines unique habitats that are exploited by microbial communities. We summarize here the current knowledge of the microbiology of shallow-water vents worldwide, highlighting gaps in our understanding of these unique environments.