Phytoplankton composition and diversity in Gorgan Bay, Golestan province

This study was carried out to investigate the phytoplankton composition in Gorgan Bay. Water samples were collected from 11 selected sites in Golestan bay, monthly from March to February. Thirty five genus were identified among which Bacillariophyta was the dominate group with 17 genus, while the Euglenophyta had the minimum. Abundance and biomass of phytoplankton showed spatial and temporal variations in the Bay. After Bacillariophyta, Cyanophyta was the most dominant group in spring, summer and autumn, while the Pyrrophyta was the most dominant in winter. Moreover, the highest number were counted for Nitzschia sp and Gyrosigma sp in spring, Gyrosigma sp, Euglena sp and Anabaenopsis sp in summer, Anabaenopsis sp and Prorcentrum sp in autumn, and Cheatoceros sp and Cyclotella sp in winter. Maximum abundance and biomass were calculated for site 8 (near Khozeini Channel) and the minimum were in sites 1 and 3 (central part of the bay) respectively. The average values of Margalef, Simpson and Shannon-Wiener indices were 0.3±0.27, 0.37±0.25 and 1.22±0.75 respectively, indicating low diversity in Gorgan Bay. The maximum Margalef (0.99), Shannon-Wiener (2.77) and the minimum Simpson (0.07) indices were calculated in February. Results of RDA showed that water temperature, water depth, transparency, phosphate, nitrate, pH, total alkalinity and dissolved oxygen had significant, high correlation with abundances of different phytoplankton genus.