Temporal distribution and composition of phytoplankton in the Southern part of Caspian Sea (in iranian waters) from 1994 to 2007
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Date
2011
Authors
Ganjian Khenari, Ali
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Abstract
Caspian Sea is the largest inner water body on the earth underwent sharp changes
in its ecosystem during the recent decades of the 20th century. They were caused by
natural ( eg. transgression of the sea level, climate change, increase of fresh water inflow)
and anthropogenic factors ( eg. pollution, invasion of ctenophore Mnemiopsis leidyi,
illegal fishing for sturgeons at sea). All that led to significant change in hydrological
regime; modify the food base, abundance and biomass of biological resources and bioproductivity
of the Sea. Long-term qualitative and quantitative characteristics of
phytoplankton community structure and biomass were investigated in 1994-2007. During
the study period, 4556 samples of phytoplankton were collected during 33 cruises in the
southern pmt of the Caspian Sea (SCS). A total of 334 species (88 genera) of
phytoplankton were identified in the SCS, which comprised of Bacillariophyta,
Chlorophyta, Cyanophyta, Pyrrophyta, Euglenophyta, Chrysophyta, Xanthophyta and
Cryptophytic. Each of the phytoplankton group was comprised of 155 species (34%), 61
species ( 19%), 55 species (16%), 30 species (9%) 25 species (7%), 4 species (1 %), 3
species (1 %) and 1 species, respectively. Bacillariophyta and Pyrrophyta were present in
all ecological groups. The phytoplankton ecological groups were fresh water species
(34%), fresh ~ brackish- water species (1 o%), brackish-water species (14%), brackishmarine-
water species (4%), marine species (8%) and other species (22%). The dominant
groups of phytoplankton from the 1994 through 2007 were Bacillariophyta which
constituted the major cell abundance and biomass (37 %, and 52%, respectively). The cell
abundance and biomass of Pyrrophyta were 34% and 37%, respectively. The highest
annual mean phytoplankton cell abundance and biomass were 249.1 x 106 ± 22.4x 106
cells/m3 and 1 034.17±117 .81 mg/m3, respectively; and higher population was due to the
presence of Pyrrophyta, Bacillariophyta and Cyanophyta between years 2001-2002. The
cell abundance and biomass of phytoplankton population showed significant difference in
years 1994-2007 (p<O.OOl). The maximum cell abundance (9.7 xi06 cells I m3
) and
biomass (83.8 mg/m3) were observed in brackish-water and marine water forms,
respectively. Long-term changes of cell abundance and biomass in 5 ecological groups
and dominant species were observed in different years. In 2001-2002, the dominant
phytoplankton were Exuviella cordata and Rhizosolenia fragilissima species; and high
density was due to Bacillariophyta and Pyrrophyta in winter. In 1999-2007, after the
invasion of ctenophore Mnemiopsis leidyi, higher cell abundance was no longer recorded
in sprirg but in winter and autumn; while higher biomass shifted from summer to winter
and spring. High diversity index of phytoplankton was associated with high level of
transparency and salinity. Phytoplankton population aggregated at the depth of 0 - 20m
with more than 87% of total cell abundance due to some favorable conditions such as
higher water temperature, light penetration, dissolved oxygen and nutrient concentrations.
Low values of Shannon-Winener index (H') were supported by low evenness index.
Vertical distribution of phytoplankton cell abundance and biomass decreased with
increasing depth. Water quality in Sf'S was classified as moderately and highly
organically polluted. In the present study, algal genus and species pollution indices (API)
were due to the oscillation in the number of phytoplankton species composition. In this
study, the principal component analysis (PCA) was used for the quality measurement of
variables such as nitrate, nitrite, ammonium, and phosphate and phytoplankton biomass.
The eutrophication index (EI) showed an increasing trend from oligotrophic to eutrophic,
with its lower value was observed for the typical oligotrophic (0.21) in 1994 and the
highest in 2005-06 (1.22). Long term EI ranged from 0.26 to 1.22 in 1994/1996 and
199611997 were grouped in the typical oligotrophic (0) and 1999/2000 were grouped as
the standard mesotrophic (M) and 2003/2004, 2004/2005, 2005/2006 and 2006/2007
were grouped with the typical eutrophic (E). Cyanophyta were represented mainly by
Aphanothece elabens, Microcystis spp., Oscillatoria limosa, Spirulina laxissma and
Anabaena spp. throughout the years. The highest cell abundance and biomass were
observed in summer and autumn. Long term biomonitoring in the SCS is required to
manage its sustainable resources and to prevent environmental degradation
Description
Keywords
Caspian Sea , Phytoplankton