Variations of phytoplankton community structure related to water quality in the south-western coasts of the Caspian Sea (Guilan province- Iran)

Phytoplankton community structure in coastal areas is a result of various environmental factors such as nutrients, light, grazing, temperature, and salinity. The Caspian Sea is located in temperate region and strongly influenced by water discharge into it. Six stations were selected to study anthropogenic effects on the phytoplankton community structure along the southwestern Caspian Sea coasts from Chaboksar through Talesh. Sampling was performed monthly in summer and autumn. Phytoplankton samples were taken quantitatively and qualitatively in each station. Concentrations of nitrate, phosphate and silicate were measured in the laboratory using spectrophotometer the average concentration of nitrate, phosphate and silicate were 0.57±0.38, 0.11±0.03 and 0.87±0.30 mg/l respectively. The concentration of nitrate and phosphate showed no significant difference among the stations, while silicate showed significant differences. Diatoms were the dominant group both in species composition and abundance followed by Cyanophytes, Dianoflagellates, Chlorophytes, Euglenoids and Chrysophytes respectively. Phytoplankton density was calculated 231± 103cell/ml during the study. The average Shannon index was 2.00±0.77 and revealed significant difference between stations. The average phytoplankton density was 245±39 cell/ml in stations, but no significant differences were found between stations. Variations in chemical and biological (diversity and density) variables were almost different between stations and could be influenced by coastal communities.