Primary production is an important process in which inorganic matter is transformed into organic matter, and it is carried out by primary producers. The primary producers in the sea are phytoplankton, macroalgae and seagrasses and are responsible for 46.2% of the total primary production. Phytoplankton, photosynthetic microorganisms that cannot actively move, but float in the water column, are mostly cyanobacteria, diatoms, dinoflagellates, cryptophytes, haptophytes and green algae. Macroalgae are multicellular macroscopic organisms that live in the benthos, consisting of brown, green and red algae. Seagrasses are plants that have fully adapted to life in the sea, and are important places of primary production, but also important habitats for numerous species because they provide them with spawning grounds, feeding grounds and shelter. In the Adriatic Sea, we can find four marine flowering plants: Posidonia oceanica, Zostera marina, Zostera noltii and Cymodocea nodosa. In the phytoplankton of the Adriatic, the largest number of species are diatoms, followed by dinoflagellates, haptophytes and chrysophyceae. The composition of the phytoplankton community is continuously monitored, and new methods are used, thanks to which new species are discovered, or existing lists are revised. Using metabarcoding, environmental DNA is analyzed, cells are isolated and cultures are established, which gives a more complete picture of phytoplankton and results that are complementary to those obtained by traditional microscopy and are the basis for future research.