Phytoplankton Diversity and Co-Dependency in a Stratified Oligotrophic Ecosystem in the South Adriatic Sea

The oligotrophy of the southern Adriatic Sea is characterized by seasonal stratification which enables nutrient supply to euphotic layer. A set interdisciplinary methods was used elucidate diversity and co-dependency bacterio- phytoplankton water column during period July 2021. total 95 taxa were determined microscopy: 58 diatoms, 27 dinoflagellates, 6 coccolithophores, 4 other autotrophs, included Chlorophyceae, Chrysophyceae, Cryptophytes. Nanophytoplankton abundances higher in comparison microphytoplankton. prokaryotic plankton community as revealed HTS dominated Proteobacteria (41–73%), Bacteroidota (9.5–27%), cyanobacteria (1–10%), while eukaryotic composed parasitic Syndiniales (45–80%), Ochrophyta (2–18%), Ciliophora (2–21%), Chlorophytes (2–4%), Haptophytes (1–4%), Bacillariophyta (1–13%), Pelagophyta (0.5–12%) Chrysophyta (0.5–3%). Flow cytometry analysis has recorded Prochlorococcus photosynthetic picoeukaryotes more abundant deep chlorophyll maximum (DCM), Synechococcus heterotrophic bacteria most surface thermocline layers. Surface, thermocline, DCM layers distinct considering diversity, temperature, correlations, extreme values at beginning investigating indicated a possible flux. Nutrient temperature recognized main environmental drivers bacterioplankton abundance.