Species determination by OBIS from water samples taken during the PHYCOB cruise in the Southwestern Black Sea in 2021

1 L samples for further phytoplankton analysis were collected from Nansen bottles installed on a SeaBird CTD Rosette from 3 layers of the water column (usually surface, termocline and deep chlorophyll maximum). The samples were preserved onboard with 20 mL formaldehyde and concentrated in the laboratory by the sedimentation method down to aprox. 30 mL. The method relies on settling and removing the supernatant in two stages, once every two weeks (Moncheva & Parr, 2010). The determination and counting of species cells in the analyzed sample fraction (1 mL) was performed under the plankton inverted microscope using 20x or 40x objectives (Moncheva, 2008). With the primary data thus obtained, the abundance (cells/L) and wet biomass (mg/m³) were calculated for each species/the highest taxonomic level that was possible to identify. The names of the identified species have been updated according to WORMS (WoRMS Editorial Board, 2022).