Benthic and Near-Bottom-Water Bacteria and Archaea on Abyssal Plains and Seamounts of the Western Clarion-Clipperton Zone: A Comparison of Community Structure and Functional Potential

The local topography of the deep-sea environment – that is, the presence of seamounts interrupting the abyssal plain – affects sedimentation rates, substrate grain sizes, and current flow in ways that are known to impact mega-, macro-, and meiofaunal community structure and activity. However, there have been fewer studies of seamount effects on metabolic activity and biodiversity of deep-sea microbes, especially seamounts without geothermal activity. A seamount habitat effect is plausible, in that changes in currents and sedimentation rate could likewise alter resource dynamics for heterotrophic and chemoautotrophic microbes. To investigate this possible relationship, we sampled bacterial and archaeal communities in the sediments and near-bottom waters of the western Clarion-Clipperton Zone (CCZ) of the North Pacific Subtropical Gyre on the DeepCCZ cruise in 2018. We targeted adjacent abyssal plain (4900-5200 m) and deep seamount (3100-4200 m) locations along a latitudinal and productivity gradient from the equatorial region north into the oligotrophic gyre. We also sampled unique habitat types within each ecosystem, including polymetallic nodules from two abyssal plains and accumulated phytoplankton detritus from a seamount. Samples are being analyzed for overall bacterial and archaeal community composition using 16S ribosomal RNA amplicon sequencing. A subset of samples will be subjected to shotgun metagenomic sequencing to investigate possible differences in community functional gene potential along this productivity gradient. Using these datasets, we will interrogate the effects of topographic features, within the context of a gradient in productivity, on benthic microbes in this sparsely studied region of the global ocean.