The Elefsis Bay is a typical coastal setting characterized by a semi-closed shallow environment with intense anthropogenic activity. This study describes a peculiar low cell density and species poor late-winter coccolithophore assemblages from Elefsis Bay compared to those from further offshore of the Aegean Sea. Helicosphaera carteri contributes significantly to the assemblage inside the Elefsis Bay and together with Emiliania huxleyi both represent the dominant component of the calcareous nannoplankton. Water column data confirmed the opportunistic behavior of H. carteri, thus providing new evidence for the ecology of the species. It is suggested that an increase in this species can be associated with distinct pollution in neritic environments.