Virio- and bacterioplankton in the estuary zone of the Ob River and adjacent regions of the Kara Sea shelf

Abstract

The distribution of structural and functional characteristics of virioplankton in the north of the Ob River estuary and the adjacent Kara Sea shelf (between latitudes 71°44′44″ N and 73°45′24″ N) was studied with consideration of the spatial variations in the number (N_B) and productivity (P_B) of bacteria and water properties (temperature, salinity, density) by analyzing samples taken in September 2013. The number of plankton viruses (N_V), the occurrence of visible infected bacteria cells, virus-induced mortality of bacteria, and virioplankton production in the studied region varied within (214−2917) × 10³ particles/mL, 0.3−5.6% of NB, 2.2−64.4% of P_B, and (6−17248) × 10³ particles/(mL day), respectively. These parameters were the highest in water layers with a temperature of +7.3–7.5°C, salinity of 3.75−5.41 psu, and conventional density (στ) of 2.846−4.144. The number of bacterioplankton was (614−822) × 10³ cells/mL, and the N_V/N_B ratio was 1.1−4.5. A large amount of virus particles were attached to bacterial cells and suspended matter. The data testify to the considerable role of viruses in controlling the number and production of heterotrophic bacterioplankton in the interaction zone of river and sea waters.