Vertical planktonic structure in the central basin of Lake Baikal in summer 1999, with special reference to the microbial food web

Planktonic microbial interactions in the central basin of Lake Baikal were examined on a summer day in 1999. The subsurface maxima of bacterial abundance and chlorophyll concentration were recorded at the same depth, whereas the vertical distribution of heterotrophic nanoflagellates was the inverse of those of bacteria and picophytoplankton. Release of extracellular organic car-bon (EOC) from phytoplankton was estimated by the NaH14CO3 method as 2.4 µg C l−1 day−1. Bacterial production (4.3 µg C l−1 day−1), estimated in a bottle incubation experiment using size-fractionated water samples, exceeded the EOC released. Thus, other supplying sources of organic matter are needed for the bacterial production. Grazing (2.6 µg C l−1 day−1) was also estimated in the experiment and accounted for 60% of the bacterial production. This is the first report on the microbial food web in the central basin of Lake Baikal.