Microbial "loop" in trophic web of lake plankton

Experimental studies were carried out in weakly eutrophic lake Anninskoe, Pskovskaya region. It was shown that 50-90% of phytoplankton production passed through microbial organisms. Depending on development of microbial "loop", production of metazoan plankton includes from 5 to 20% of primary production. Changes of structure of plankton community were studied under hard, weak and moderate press of large zooplankton. It was shown that of development bacteria and ciliata were inversely dependent on the ratio of zooplankton to algae biomass. This ratio, reflecting intergras regulative impact of biotic factors to the microbial community from the "top" and from the "bottom", is proposed by the authors as an index of biotic relationships in plankton. The importance of Asplanchna prodonta in development of structure and abundance of phytoplankton and protozoa is discussed.