Study on Cyanobacteria Population in Iranian Waters of the Caspian Sea during 2010-2011

Tahami F

Published on: 2020-05-15

Abstract

Since awareness of the cyanobacteria population of each ecosystem is important, the aim of this study is focuses on cyanobacteria population of Iranian waters of the southern Caspian Basin. The present study was conducted in southern part of Caspian Sea, Iran. All samples were taken during 2010-2011 through spring, summer, autumn and winter, in 32 stations from 8 transects (Astara, Anzali, Sefidrood, Tonekabon, Noshahr, Babolsar and BandarTurkman). In each transect 5 stations in different depths of 5 m, 10 m, 20 m, 50 m and 100 m were defined that the seasonal sampling were performed from the depth of zero (surface), 10 m, 20 m, 50 m and 100 m by Ruttner Water Sampler, and then transferred to laboratory of Caspian sea ecological institute. Then the samples transferred to laboratory of Ecological Academy, kept in cool and darkness in properly capped glass bottles. The cyanobacteria were analyzed on a “Nikon” light microscope at ×480 magnification. Algae abundance was determined using the Hydro bios counting chamber and sampled (volume 0.1 ml). The volume of each cell was then calculated by measuring its appropriate morph metric characteristics and geometric. A total of 19 species, that belong to 10 different genera, showed significantly decrease with increasing depth, especially at the depth of less than 20 m (P<0.05). The Cyanobacterial compositions were significantly changed with seasons and depths, and depth and the maximum cell abundance and biomass observed in summer. The Microscopic Cyanobacteria species were identified. (P<0.05) and Shannon index was different for different seasons.

Keywords

Cyanobacteria; Population; Depth; Season; Caspian sea; Iranian waters

Introduction

Cyanobacteria  are blue-green algae that contain prokaryotic cells and are able to photosynthesize because of their chlorophyll. These organisms are a part of the planktonic communities of aquatic ecosystems [1]. Cyanobacteria can have effect on the water quality of different aquatic ecosystems like Caspian Sea [2]. The Southern Caspian Sea adjacent to the three provinces of Iran; Golestan, Mazandaran, and Gilan, is located in the northern part of the Alborz Mountains. The rivers such as Sefidrood, Gorganrood, Tajan, Haraz, Shirood, Sarabrood, Talar, and Babolroodare ended in this sea. Since Cyanobacteria are important in aquatic ecosystems and study on cyanobacteria is necessary, especially the species identification, biomass density, regional alternation, and various factors that affect the ecosystem. Also Nutrient enrichment may give rise to shifts in Cyanobacteria species composition and biomass. Furthermore, an increase in the frequency, magnitude and duration of harmful Cyanobacteria blooms may occur. In southern Caspian Sea, the wet and dry seasons can change the nutrients and benthic communities. Sea blooming of some Toxic Cyanobacterias in Southern Caspian Sea can occur because of the influence of industrial and agricultural pollutants in those rivers that arrives to the Southern Caspian Sea especially in warm seasons (Microcystis, Nodularia, and Anabaena). Even though the Cyanobacteria are classified as bacteria (lacking a membrane-bounded nucleus) they are photosynthetic and are included among our algal collections [2]. Early studies by researchers have shown that cyanobacteria generally have beneficial effects on reducing infections and the intervention of these microorganisms through physical or chemical processes is not very complicated. Given the importance of cyanobacteria in aquatic ecosystems, the aim of this study was to identify different species of cyanophytes and their density in the southern Caspian Basin.

Material And Methods

This study was conducted in the southern Caspian Sea basin, which where the sampling at different stations and depths were performed for one year and by the Gilan research vessel and Rottner sampler (maximum volume of 2 liters) in spring, summer, autumn and winter, of 2010. Sampling areas were selected at the 8 transects: Astara, Bandar Anzali, Sefidrood entrance, Tonekabon, Noshahr, Babolsar, and Amir Abad port (Figure 1). In each transect, 5 stations at the depths of 5, 10, 20, 50 and 100 m were considered and the sampling was conducted by a Guilan research ship. Caspian Institute of Ecology Research Planktonology Laboratory analysis was performed according to the APHA (American Public Health Association) [3].

Figure 2: Genera identified in this study.

In this method, for deposition, the specimens were kept in the dark for 10 days. Then it with a special siphon, and the remaining sample centrifuged at a speed of 3,000 rpm for 5 minutes then Discard supernatant to reach a volume of 20-25ml. In the laboratory, the samples were investigated and microscopically counted in two qualitative steps and one quantitative step by the slabs and lamellas of 24×24 mm [4]. Calculations of mean and standard deviations and preparation of their figures were performed by Excel 2007 software. Frequency data and the Algae biomass showed a normal distribution. Comparisons of the mean data were performed by multiple analyses of variance (ANOVA) and Duncan test. In variance analysis, the density and biomass of different branches were considered as dependent variables. The species diversity index was calculated according to the Shannon-Weaver formula [5] and by following formula:

is the Shannon-Weaver index (nits per individual), and is the relative abundance of species.

 

Results

In this study 19 species belonging to 10 genera of Cyanophyta were identified. The studies have indicated that Cyanobacteria have an essential role in the primary production in the ecosystem according to the environmental conditions.  The number of Cyanobacteria species observed in different seasons varied and the least species were observed in spring and most species in autumn and winter (Figure 3). In the seasonal study of different branches of Microscopic Algae, the highest density was in the autumn, 285.7 ± 137.1 in (m3) and the maximum biomass was in the summer, 105.81 ± 38 (mg/m3) (Table 1). As shown in Figure 2 the highest Shannon index (H′) was observed in the spring and it gradually decreased during the summer, autumn and winter. The highest Shannon index was in the west area in spring (0.96), and the lowest Shannon index was in the East region in the autumn season (0.47) (Figure 4) [5].

Figure 3: The number of species of cyanobacteria in different seasons.

Figure 4: Shannon index (H) for microscopic algae in different seasons in 2010- 2011.

Table 1: Density (number in m3 × 106) and biomass (mg/m3) of Cyanobacteria in different seasons in 2010 - 2011.

Spring

Summer

Autumn

Winter

Density

(m3)

Biomass

(mg/m3)

Density

(m3)

Biomass

(mg/m3)

Density

(m3)

Biomass

(mg/m3)

Density

(m3)

Biomass

(mg/m3)

13.6 ± 7.4

7.5 ± 10

158.2 ± 134.4

105.81 ± 38

285.7 ± 137.1

95 ± 54

10.4 ± 2.4

5 ± 2.2

 Table 2: Checklist of cyanobacteria species during 2010-2011.

Anabaena bergii

Nodullariaspumgina

A. aphanizomenides

Oscillatorialimosa

A. spiroides

O. agardhii

A. hisselevii

O. sp.

Aphanizominonflos-aqua

O. tennuis

Ap. sp.

Spirulina laxissma

Aphanothece sp.

S. sp.

Chroococcus sp.

Gloeacapsalimnetica

Lyngbyalimnetica

-

L. sp.

-

Merismopedia minima

-

 

 

Discussion

Cyanobacteria exhibit in addition to the adaptability to regulate buoyancy, the regulation of pigment pools in response to both quantity and quality of light. Hence it could be said the presence of higher number of species of the Cyanophyta in the dry and rainy season, respectively is indicative of the water quality in the different seasons. Our study demonstrates that across Southern Caspian Sea, varied environmental conditions and morphometry, pronounced season and temperature gradients favor the distribution of bulk Cyanobacteria into more defined layers and seasons, while the depth of the peak and the heterogeneity of individual Cyanobacteria were differentially affected by habitat structure [8,9]. Cyanobacteria habitat structure was relatively different between the different seasons [10]. Distribution of Cyanobacteria is fundamental importance for the dynamics and structure of aquatic communities [6] that the dynamic of rapid increase or decrease of plankton populations is an important issue in marine ecology. This problem poses a challenge for ecologists, as the location of a production layer is not fixed [7], but rather depends on many internal parameters and environmental factors [11], and even with respect to daily time that Cyanobacteria are a phytoplankton too. Cyanobacteria are very similar to bacteria, meaning they lack a distinct nucleus and differentiated cytoplasmic attachments and differ in their pigmentation, meaning that the cyanobacteria have pigments and the bacteria have no pigments. The results of this study showed that the dominant specimens of cyanobacteria were genotypes Anabaena, Aphanizominon, Aphanothece, Chroococcus, Lyngbya, Merismopedia, Nodullaria, Oscillatoria, Spirulina and Gloeacapsa. In the year 1998, the identification of different cyanobacteria species by a cadre in Lake Keban, Turkey found that temperature and increased light were positive factors for species growth, especially cyanobacteria. However, the highest density of cyanobacteria was observed in autumn and then in summer, which may be due to the growth of large-sized species in summer [12]. Increased Cyanobacterial population is usually linked to human activities such as agriculture that result in excess nutrient inflow into the waters [13,14]. During 2010-2011 the percentage of cell abundance and biomass of Cyanobacteria in different seasons were significant changed (P<0.05) and the species of cyanobacteria decreased with decrease temperature in winter [18]. They may proliferate and form blooms under certain conditions, particularly when high levels of nutrients are available. Cyanobacteria are of toxicological interest because several genera of cyanobacteria have the ability to produce toxins, and it is generally more common during warmer weather in summer, but can occur at any time of the year [17]. On base on this study, one can tell that with increasing temperature in summer in Caspian Sea, increases its biodiversity. Sze stated in his observations that in the warm season (summer), due to rising ambient temperatures and water, the density of cyanobacteria increases, which is consistent with the results of the above study [15]. That is, with the onset of the warm season of the year, the temperature and biomass of cyanobacteria increase as well. Cyanobacteria are nitrogen fixers due to their heterocyst nodes, which can be a factor in their growth [16]. Shannon-Weaver index shows three water quality classes. Figure 4 has shown Shannon-Weaver index diversity index, which implies that the high value suggests healthier ecosystem and the low value suggests poor diversity in a community and a less healthy ecosystem. In this study, Shannon index of phytoplankton ranged from 1.84 to 2.48. Due to change of seasons and factors such as temperature change (change of seasons), high concentrations of dissolved nitrogen in all of these examples can effect on the cyanobacteria, and then in different seasons are different.  Maximum density showed in atumn (285.7 ± 137.1) (m3) and Maximum biomass showed (105.81 ± 38) (mg/m3) in the summer that various factor, including different rates of reception, sun energy, consequently temperature, Water flows and river water in this area can cause cyanobacteria to differentiate at different times. Cyanobacterial strains exhibit different levels of susceptibility to contamination. In most cases, the presence of contamination increases the growth of cyanobacteria, indicating that these microorganisms are more likely to decompose and utilize these compounds [19]. The present study showed that the diversity and number of cyanobacteria present in the ecosystem of the southern Caspian Basin varies in different seasons and different season conditions including climatic conditions, moisture content and amount of light absorbed on the surface are involved.

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