As the main primary producer, phytoplankton is an important link between the physical and chemical elements and higher tropic levels in the marine food web. Changes in the environment could affect the annual succession and species composition of the phytoplankton, as well as the overall primary production in the area. Phytoplankton monitoring will give important information regarding biological changes on the lowest level in the food web with environmental impact and climatic changes.
The variability in the timing and development, abundance and species composition is large in the Barents Sea. This is due to the large gradients that are observed in the physical and chemical environment along east – west and north – south gradients in the area. The horizontal distribution (Biogeography) of phytoplankton in the Barents Sea is in large degree controlled by the polar front, freshwater runoff and ice cover and ice melting. The Arctic water and the Atlantic water will bring characteristic species into the Barents Sea, as well as the coastal water, all contributing to the diversity in the area. In the Barents Sea phytoplankton species of Arctic origin, cosmopolite, and boreal origin is observed. However, the percentage of the different groups will vary considerable depending on the location of the study site within the Barents Sea.
According to the traditional views of classical marine ecology (Usachev, 1935; Shirshov, 1937; Raimont, 1983; and others), the entire process of development of the phytoplankton, and their qualitative and quantitative characteristics, is fully determined by direct impact of abiotic factors, such as light, ice conditions, temperature, salinity, and concentration of macro and micro nutrients. However, M.M.Kamshilov (1961) suggested that the main factor, defining the structure and functioning of pelagic ecosystems, is the biotic interactions between organisms. The reality is processes and evolution driven both by bottom-up (environmental) and top-down (biotic interactions/predation) forces. The strength and importance of the different factors, physical, chemical, and biological, will vary during the different phases, e.g. high grazing pressure during summer and stratification during spring. Obviously, with such a tight connection between the components of the community, it is not sufficient to use one or a few indicators to obtain reliable results of its condition. Such criterion should have a complex character and reflect all the ongoing processes, as well as to be relatively stable in time and space and keep this stability in the constantly changing natural environment. In the future monitoring and research program it will be important to seek for new and better indicators or criterions for the pelagic phytoplankton.