Annotation. The taxonomic structure and the lists of species of the phytoplankton community in the Russian sector of the Caspian Sea have been presented. The dominant complexes have been detected. The predominance of small-cell types is characteristic of the modern structure of the summer phytoplankton. A high floristic diversity has been observed. Bacillariaphyta were the dominants. They made 42% of the species diversity. Cyanophyta algae were the basis of the group, whereas Bacillariaphyta were the basis of the biomass.

Abstract. Aim.The composition of the species of the phytoplankton in the Russian sector of the Caspian Sea in conditions of transgression, anthropogenic and chemical contamination has been studied. 

Location. Russian sector of the Caspian Sea.

Methods. The phytoplankton samples were collected at the depths of 8–100m and at the levels of 0, 10, 25, 50, 100 m by the use of the Nansen bathometer and subsequently were fixed in 4 % formalin. The fixed samples were kept in the dark for at least 15 days. The material was concentrated by the common method of deposition. The office processing was carried out in a box of Nozhotta type, which has the volume of 0.1 ml and the triplicate surface, under the light microscope of Biolam P15. The system of domestic diamotologists was used during the classification of Bacillariaphyta, as for the classification of Dinophyta, the Dodge scheme was applied. Cyanophyta algae were classified according to the system of A.A. Elenkina with the amendments adopted by A.I. Proshkina-Lavrenko and V.V. Makarova. The classification of the Chlorophyta division has been done according to the Smith system.

Results. Presented the taxonomic structure and the lists of species of the phytoplankton community in the Russian sector of the Caspian Sea have been presented. The dominant complexes have been detected. A high floristic diversity of 71 species as well as the form and the variety of microalgae of 5 departments have been observed. Bacillariaphyta, which made 42% of the species diversity, were the dominants. Cyanophyta algae were the basis of the group, whereas Bacillariaphyta were the basis of the biomass.

Main conclusions.The predominance of small-cell species is characteristic of the modern structure of the summer phytoplankton.A high floristic diversity has been observed. The phytoplankton community was represented by five groups: Bacillariaphyta – 30 species (42 %); Dinophyta – 18 species (26 %), Cyanophyta – 16 species (23 %), Chlorophyta – 6 species (9 %) and 1 species of Cryptophyta.