The cyclonic eddy uplifts nutrient-rich seawater into the euphotic zone, typically directly enhancing phytoplankton abundance and primary production. However, its impact on bacterial production by heterotrophic prokaryotes remains unclear due to the complex interplay of multiple indirect factors governing this process. Here, we conducted a comprehensive investigation of the distribution of picophytoplankton and heterotrophic prokaryotes, prokaryotic community structure, and bacterial production within a cyclonic eddy in the western North Pacific subtropical gyre. The results indicated that despite the higher abundance of picophytoplankton accompanied by nutrient upwelling at the eddy core compared to the edge, higher levels of bacterial production were observed at the eddy edge between 100–200 m, consistent with the distribution of the low nucleic acid content (LNA) prokaryotes. The significant positive correlation between bacterial production and the proportion of LNA group in heterotrophic prokaryote abundance suggested a primary contribution from the LNA group over the high nucleic acid content (HNA) group. SAR11, a typical member of the LNA group, may primarily contribute to the elevated bacterial production observed at the eddy edge. The changes in temperature and light intensity induced by the cyclonic eddy may significantly influence the distribution and activity of HNA and LNA groups, potentially exerting a greater impact on bacterial production compared to phytoplankton-related factors. These findings contribute to understanding the underlying mechanisms of bacterial production responses to cyclonic eddies in the oligotrophic open ocean.
 

cyclonic eddy, picophytoplankton, heterotrophic prokaryotes, bacterial production, LNA (Low Nucleic Acid) group