IMIS

Phytoplankton samples were collected by CTD probe (SBE-911) with attached Niskin bottles at discrete depths, defined according to the in situ fluorimeter readings (0m - thermocline- deep chlorophyll a maximum), and 1m above the bottom or down to 75 m depth at the deeper stations. Phytoplankton samples (1000 ml water sample) were fixed on board in 4% formaldehyde solution, buffered to pH 8-8.2 with disodiumtetraborate. In the laboratory the samples are concentrated down to 50 cm3 by slow decantation after storage for at least 20 days in a cool and dark place. Taxonomic identification and cell counts are done under inverted microscope (Nikon T300E) connected to a video-interactive image analysis system ((L.U.C.I.A, Version 4.8, Laboratory Imaging Ltd, Prague) at 400x magnification by the Uteröhl (1958) method in Sedgwick-Rafter counting chambers. 400 cells are counted from each sample, while rare and large species are checked in the whole counting chamber (Moncheva and Parr, 2005/2015). The individual cell biovolume (V, μm3) is derived through the approximation of the cell shape of each species to the most similar regular solid, calculated by the respective formulas (Edier , 1979 ; Vadrucci et al., 2007), averaged over measurement of ten cells from each species. Cell bio-volume is converted to weight (W, ng) following Hatchinson (1967). Taxonomic nomenclature is according to the on-line data-base of World Register of Marine Species (WoRMS) http://www.marinespecies.org/ and the Black Sea phytoplankton check-list. The QC/QA of the data is performed following the quality control Guidelines for phytoplankton (Moncheva, 2010).