The Effect of Different Ecological Parameters on the species diversity and Distribution of Phytoplankton in the South Coast of Caspian Sea (Mazandaran Province)

This research was conducted to evaluate the effect of ecological factors on diversity and density of phytoplankton in Caspian Sea. Sampling was carried out from 5 stations included of Ramsar, Nowshar, Noor, Fereydunkenar and Miankaleh (Amirabad) regions (surface, 3 and 5 m depths) from 2016 to 2017. The totals of 56 species belong to 5 phyla of algae division were identified which maximum density and biomass were observed in Skletonema costatum, Thalassionema nitzschioides, Nitzschia acicularis, Pseudonitzschia seriata and Melosira moniliformis. Density and biomass of phytoplankton showed that the mean of biomass was 12.3±2.7×106 cell/m3 and 35.6±7.7 mg/m3, respectively, with the highest average density in winter (19.1±4.4 ind.m-3). The highest and lowest Shannon index was 1.97 and 1.84 in different seasons respectively. Silica, temperature and inorganic nitrogen play an important role in density of algae especially diatoma, cyanophyta and pyrrophyta. The recent study showed that a high N:P ratio in winter and characteristics along with a suitable strategy for Chlorophyta species are important and desirable reasons for increasing their populations.