Temporal and vertical dynamics of diatoms and dinoflagellates in the southeastern Mediterranean Sea

The temporal distributions of microphytoplankton were studied monthly over 2 years in the shelf and the offshore waters of the "low nutrients low chlorophyll"(LNLC) southeastern (SE) Mediterranean Sea. The microphytoplankton were comprised mostly of diatoms (0-542 cells L-1, ~4 × 106-44 × 106 cells m-2) of the genera Rhizosolenia, Thalassionema, Chaetoceros, Leptocylindrus and Pseudo-nitzschia, and dinoflagellates (1-89 cells L-1, ~1 × 106-10 × 106 cells m-2) of the genera Tripos (formally known as Ceratium), Ornithocercus, Protoperidinium, Ceratocorys and Dinophysis. During the winter mixing, microphytoplankton abundance was ~2-fold higher than during the stratified summer months, in accordance with the higher inorganic nutrient levels. Diatoms were mostly found in the upper illuminated layers (0-100 m), while dinoflagellate distribution was patchy and spread from surface down to 200 m. We also calculated that diatoms and dinoflagellates contribute negligibly (~4%) to the total vertical carbon flux in the offshore water, suggesting fast recycling of organic matter at the photic layer. Our results provide a baseline to better understand carbon and biogenic silica fluxes at the LNLC SE Mediterranean Sea.