Phytoplankton and zooplankton monthly samples collected from the coastal water stations, located in Ras Al Khaima Emirate (United Arab Emirates) and Sohar governorate (Sultanate of Oman), during 2018-2019, have shown great variations, not only in their community structures, but also in their species abundances. Plankton samples were collected via vertical hauls from 6 m depth to the surface at Ras Al Khaima, while in Sohar, samples were collected from 20 m depth to the surface. The sample analyses revealed the dominance of diatoms during the warmer months at both sample sites, with an increase of dinoflagellates during the colder months, especially at Sohar. The abundances of certain species at each site, could not be explained by the grazing of zooplankton (dominated by calanoid copepods) on species-specific populations of phytoplankton, nor by seasonal temperature variations. The hydrological regime at the Strait of Hormuz, separating the two sample sites, as well as the differences in morphometric features and other environmental parameters, could account for the ecological differentiation in planktonic successions at both locations.