Distributions and relationships of virio‐ and picoplankton in the epi‐, meso‐ and bathypelagic zones of the Western Pacific Ocean
&NA; Virio‐ and picoplankton mediate important biogeochemical processes and the environmental factors that regulate their dynamics, and the virus–host interactions are incompletely known, especially in the deep sea. Here we report on their distributions and relationships with environmental factors at 21 stations covering a latitudinal range (2–23° N) in the Western Pacific Ocean. This region is characterized by a complex western boundary current system. Synechococcus, autotrophic picoeukaryotes, heterotrophic prokaryotes and virus‐like particles (VLPs) were high (<2.4 × 102–6.3 × 104, <34–2.8 × 103, 3.9 × 104–1.3 × 106 cells mL−1 and 5.1 × 105–2.7 × 107 mL−1, respectively), and Prochlorococcus were low (<2.3 × 102–1.0 × 105 cells mL−1) in the Luzon Strait and the four most southerly stations, where upwelling occurs. Covariations in the abundances of VLPs with heterotrophic and autotrophic picoplankton, and their correlation (i.e. r2 = 0.63 and 0.52, respectively) suggested a strong host dependence in the epi‐ and mesopelagic zones. In the bathypelagic zone, only abiotic factors significantly influenced VLPs abundance variation (r2 = 0.12). This study shows that the dynamics of virio‐ and picoplankton in this Western Pacific are controlled by suite of complex and depth‐dependent relationship among physical and biological factors that in turn link the physical hydrography of the western boundary current system with microbial‐mediated biogeochemical processes.