Distributions and relationships of virio- and picoplankton in the epi-, meso- and bathypelagic zones of the Western Pacific Ocean.

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.