Seasonal distribution of dominant phytoplankton in the Southern Caspian Sea (Mazandaran coast) and its relationship with environmental factors

Seasonal distribution of phytoplankton and factors affecting their presence in the Mazandaran coastal ecosystems were investigated in 2012. In this study, Distribution of the phylum and dominant species of phytoplankton and water quality parameters were evaluated along 4 transects (Amirabad, Babolsar, Noshahr and Ramsar) in the different layers of the water column at final depths of 5, 10, 20 and 50m. Variation of the dominant species and environmental parameters was analyzed using Principal Components Analysis (PCA). Average annual phytoplankton density was 185162558 cubic meters, the highest density in winter and lowest in spring was determined. Totally, 7 groups and 131 species of phytoplankton were identified, including Bacillariophyta (58 species), Cyanophyta (24), Pyrrophyta (22), Chlorophyta (17), Euglenophyta (8) and 1 species each of Haptophyta and Xanthophyta. The dominant species in the water body were Exuviaella cordata of the Pyrrophyta (61.25% of the species) in spring, Oscillatoria sp. of the Cyanophyta in summer and autumn (48.69 and 71.91%, respectively) and Pseudo-nitzschia seriata of the Bacillariophyta (66.12%) in winter. This study showed that Thermocline, riverine transport, Mnemiopsis leidyi and opportunistic phytoplanktonic species with high competitive ability (Cyanophyta and Pyrrophyta (were the most effective factors on spatio-temporal variations of phytoplankton. Temperature, silica and inorganic nitrogen play an important role in population dynamics are diatoms, while temperature, inorganic and organic phosphorus and inorganic nitrogen for Cyanophyta and Pyrrophyta are important.