Picocyanobacteria are a diverse and widespread group of photosynthetic prokaryotes and belong to the main group of primary producers (Castenholz & Waterbury. 1989; Rippka, 1988). Picoeukaryotes, meanwhile, are a diverse group that is widely distributed in the marine environment, and they have a fundamental role in aquatic ecosystems because of their high productivity. Like bacteria, marine viruses are thought to play important roles in global and small-scale biogeochemical cycling. They are also believed to influence community structure and affect bloom termination, gene transfer, and the evolution of aquatic organisms. Viruses are the most numerous ‘lifeforms’ in aquatic systems, being about 15 times more abundant than total of bacteria.
