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Unraveling the distribution patterns of bacterioplankton in a mesoscale cyclonic eddy confined in an oxygen-depleted basin

Silvia Pajares*

*Corresponding author:

ABSTRACT: Mesoscale eddies in oxygen minimum zones profoundly affect the structure and productivity of marine planktonic communities and alter key biogeochemical cycles. The influence of a mesoscale cyclonic eddy confined in a semi-enclosed oxygen-depleted basin (Gulf of California, Mexico) on the spatial distribution of bacterioplankton was investigated. Most of the bacterial taxa showed a strong vertical distribution from oxygen-rich surface waters to anoxic bottom waters, but also a horizontal distribution pattern in the upper ocean associated with the eddy presence. Synechococcocales, Flavobacteriales, SAR86, and Actinomarinales were abundant in the euphotic zone, within the Gulf of California water mass; whereas SAR324, SAR406, SAR202, SUP05, Arctic97B-4, and Thioglobaceae, dominated the bottom layer of this basin, within the Subtropical Subsurface water mass. In contrast, bacterial taxa with a preference for mesopelagic waters (Thiomicrospirales, SAR324, SAR202, HOC36, UBA10353 marine group, and Nitrospinales) dominated surface waters of the eddy center, where common surface taxa (Synechococcus, SAR86, and Actinomarinales) were scarce. These changes in community composition led to a distinct diversity of bacterioplankton between the center and the edges of the eddy within the euphotic zone. These results show the strong role of oxygen and water masses in controlling the vertical distribution of bacterioplankton, whereas the eddy modifies more strongly the bacterial assemblage in the upper ocean.