Picoplankton composition related to thermohaline circulation: The Albanian boundary zone (southern Adriatic) in late spring

► We examined the influence of hydrographic conditions on picoplankton distribution. ► Picophytoplankton accumulated from 50 to 75 m, forming a deep chlorophyll maximum. ► LIW intrusion was followed by the appearance of two Synechococcus ecotypes. ► The East Adriatic Current (EAC) acted like a barrier for Prochlorococcus. ► The picoeukaryotes maxima coincided with the core of the EAC.