In cold years big diatom and peridinium algae are the basis in phytoplankton biomass in the region with mussel mariculture farming. Mussels consump ultra and nanoplanktonic coccolithophorides, peridinia and small flagellates, mass development of which was watched during warm years. Actively filtrating and transforming into faeces and pseudofaeces a mass of planktonic algae mussels serve as meiorators in the environment.