Author(s): Alexander I. Kopylov; Dmitriy B. Kosolapov; Anna V. Romanenko; Elena A. Zabotkina
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Abstract: Distribution and dynamics of planktonic bacteria, protozoans and viruses were studied in a large shallow mesotrophic reservoir (Rybinsk Reservoir, the Upper Volga, Russia) during the ice-cover period. The duration of an ice period varied from 155 to 170 days. The ice thickness can exceed70 cm and the thickness of snow–50 cm. The primary phytoplankton production was not usually high under ice. The vertical distribution of bacteria was uneven: the maximal bacterioplankton biomass (5.5 mg wet weight per liter) was found on the ice–water interface. Mass development of heterotrophic bacteria in the microlayer under ice was related to the accumulation of detritus and algae Melosira islandica. The bacteria attached to detritus particles and forming microcolonies accounted for 62-82% of the total bacterial biomass. These aggregated bacteria can be an important source of food for the metazooplankton. An increase in size of bacterial cells, number of active bacteria and bacterial specific growth rate was observed from January to March. The consumption of bacteria by flagellates was revealed using fluorescently-labeled bacteria. A high abundance of extracellular viral particles was found during winter (up to 107particles ml-1). Up to 35% of bacterioplankton was infected by phages. The analysis of carbon flows in the pelagic food webs has shown a great importance of heterotrophic microorganisms and phages in functioning of winter planktonic community.
Year: 2010