The present paper deals with the vertical distribution of summer phytoplankton in different layers (SHL, TCL and Ca) at selected subregions of the western Black Sea. A comparison between the north-western, western and southern Black Sea is also presented. A special statistical software package was used to display the core species along the vertical axis and to select environmental variables explaining the community distribution. Despite the subregional differences the results reveal that about 50% of the total biomass was maintained in the SHL, about 40% in the TCL and from 10% to 20% in the CIL depending on the position and depth of each layer. The environmental factors, especially nutrients have more important implications for algal species composition and abundance in the SHL, while for the deep flora the formation of CIL waters and the mechanisms of biological control may be the more significant processes.