Unexpectedly high abundance of viruses in seas and oceans was been recorded 20 years ago reaching up to 108 particles/ml. Viruses of marine microorganisms – autochthonous viruses of plankton and benthos-appeared to be the most numerous components of aquatic communities. They play a key role in control of abundance and species diversity of their hosts and cause 20 % mortality of heterotrophic bacteria and
3–5 % mortality of phytoplankton cells every day. This novel knowledge on the role of viruses in circulation of organic carbon in the World Ocean radically changed the ideas existing earlier on structure and functioning of “microbial food loop” in aquatic ecosystems.