Abstract.Benthic samples were taken at 26 stations during a two year period (1975–1977) in the Gulf of Thermaïkos, Greece. The topography and relevant physicochemical characteristics of the area are presented and discussed. Both density and biomass increase towards the northern limits in the Bay of Thessaloniki and in the Gulf of Thermaïkos, the difference between them being the degree of change in a north‐south direction. Analyses of the degree of concurrence of the dominant species show the existence of a number of groups of concurrent dominant species with characteristic distributional patterns and differing areal coverage in the study area. The observed quantitative and qualitative differences in the benthos are causally related to the differing environmental conditions prevailing in the two sub