Spatial Distributions of Picoplankton and Viruses in the Changjiang Estuary and Its Adjacent Sea Area during Summer

Abstract

Simultaneous determination of picoplankton (i.e., Synechococcus spp., Prochlorococcus spp., picoeukaryotes, and heterotrophic bacteria) and viruses in the Changjiang (Yangtze) River estuary and its adjacent sea area was made using flow cytometry during a cruise in June 2006. The results show that Prochlorococcus in all samples was below detectable level. The abundances of Synechococcus, picoeukaryotes, heterotrophic bacteria, and viruses ranged from 0.00 to 1.22×108 cell L−1, 0.01×106 to 1.42×107 cells L−1, 8.40×107 to 4.29×109 cells L−1, and 1.20×107 to 1.06×1010 particles L−1, respectively. The determined picoplankton groups and viruses distinctly increased with the distance off the estuary and where the maximum abundance that occurred in these groups was different somewhat due to the individual sensitivity to environmental changes. Viral abundance showed a positive correlation with salinity and negative correlations with turbidity and inorganic nutrient concentrations. Positive linear relations were found between Synechococcus, heterotrophic bacteria, and viruses.