Introduction and a brief history of plankton research, the most famous expedition. General characteristics of plankton. Plankton as a living form (virioplankton, bacterioplankton, phytoplankton, zooplankton). Autotrophic, heterotrophic, and mixotrophic organisms. Methods of sampling and determination of phytoplankton (abundance, biomass, primary production). Phytoplankton taxonomy. Phytoplankton in the Mediterranean and in the Adriatic Sea. Toxic phytoplankton species. Pigments. Zooplankton systematics. Methods of zooplankton investigation and analysis. Population density and biomass. Interspecies relations. Spatial and temporal distribution of dominant zooplankton groups. The main characteristics of zooplankton in the Mediterranean and the Adriatic Sea. Physical and chemical factors affecting the spatial and temporal distribution of plankton. Trophic relationships in the pelagic. Transfer of zooplankton by ballast water.