Distribution, Abundance And Biomass Of Phytoplankton In The Southern Part Of Caspian Sea (In Iranian Waters)
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Date
2007-06
Authors
Khenari, Ali Ganjian
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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 100 meter 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 and 13 Euglenophyta).
Bacillariophyta contributed 43% of phytoplankton species abundance. The
number of phytoplankton species recorded were 77 in winter, 91 in spring, 101
in summer and 86 in autumn. They decreased from autumn to winter.
Cell abundance and biomass of Bacillariophyta were recorded high in the
middle of the Caspian Sea, while dinoflagellates were recorded abundant in the
west and middle regions. PCA analysis 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 11x1062::9x106 sellm3 dan 44.262::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 occurred in spring. The highest and lowest temperatures
recorded were 29.0°C (summer) and 9.9°C (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 dan 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 laterbonii 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.