DISTRIBUTION, ABUNDANCE AND BIOMASS OF PHYTOPLANKTON IN THE SOUTHERN PART OF CASPIAN SEA (IN IRANIAN WATERS)

ALI GANJIAN KHENARI (2007)

ABSTRACT

Seasonal distribution of phytoplankton and the physico-chemical parameters of the Caspian Sea were investigated at 6 transects with 26 stations, at the depths of surface 5,10, 20, 50 and 100m from winter (January-February), spring(May), summer(July), autumn (October-November) in 2005. A total of 260 phytoplankton samples were collected from the stratified water column during the sampling along Iranian coasts (southern part ) of the Caspian Sea. A total of 163 phytoplankton species were identified (71 Bacillariophyta, 21 Pyrrophyta, 31 Chlorophyta , 27 Cyanophyta, 13 Euglenophyta). Bacillariophyta contributed 43 % of phytoplankton species abundance. The number of phytoplankton species recorded were 77 in winter (January-February), 91 in spring (May), 101 in summer (July) and 86 in autumn (October- November). They decreased from autumn to winter. Due to the supply of SiO2 ,nitrate and nitrite, cell abundance and biomass of Bacillariophyta were recorded high in the middle of Caspian Sea, while dinoflagellates were recorded abundant in the west and middle regions. PCA analyses showed that Bacillariophyta and Pyrrophyta contributed 53.64% of the total variance. CDFA analysis performed on different groups of phytoplankton resulted in the canonical variable plot with a thick cluster at the west, due to high concentrations of Bacillariophyta and Pyrrophyta, whereas the middle region was separated because of the highest biomass of Pyrrophyta species. During the 1-year study, the most dominant groups were Bacillariophyta and Pyrrophyta. The overall average of cell abundance and biomass of phytoplankton were 11×106 ± 9×106 cells/m3 and 44.26±52.83 mg/m3 respectively. The overall contribution of Pyrrophyta biomass and Bacillariophyta cell abundance were 53% and 47% respectively. The presence of Bacillariophyta contributed to the phytoplankton cell abundance in winter and the Pyrrophyta maximum biomass occured in spring. The highest and lowest temperatures recorded were 29.0 ºC (summer) and 9.9 ºC (winter) respectively. The salinity fluctuated between 9.1 and 12.6 ppt. The maximum density of Bacillariophyta was recorded in winter and autumn due to the presence of Thalassionema nitzschiodes, Cyclotella menenghiniana, and other different species of Nitzschia and Chaetoceros. Maximum biomass was observed in the spring as dominant species were the large size of Bacillariophyta e.g. Rhizosolenia calcar-avis, Rhizosolenia fragilisima and Nitzschia sigmoidea. The second dominant phyla in terms of cell abundance and biomass were Pyrrophyta. Maximum cell abundance in the different layers and transects were due to the presence of Exuviaella cordata (Pyrrophyta) while the dominant biomass belongs to Prorocentrum praximum and Prorocentrum scutellum. Exuviaella cordata had the highest growth in all seasons, transects, and spread at different layers, compared to other species of phytoplankton. Cyanophyta was the dominant group in summer due to the presence of Oscillatoria limosa. The dominant species of Chlorophyta and Euglenophyta were Binuclearia laterbornii and Trachelomonas respectively. Maximum phytoplankton cell abundance and biomass was concentrated at the depth of less than 20m. In this study, it is found that cell abundance of phytoplankton decreased with increasing water layer (depth). The changes in the physical and chemical regimes of the Caspian Sea influenced the variations of phytoplankton composition and distribution.

Masters thesis, Universiti Sains Malaysia.