A regular sampling for the determination of picoplankton abundance at the time series station C1 in the Gulf of Trieste, North Adriatic Sea began in 1993. The time series station C1 was initiated by the University of Trieste, and was later taken care by the Laboratory of Marine Biology of Trieste after its formal institution in December 1979 and, since October 2005, by the Department of Biological Oceanography, now Division of Oceanography (OCE) of OGS, Istituto Nazionale di Oceanografia e Geofisica Sperimentale of Trieste.