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Seasonal Variations of Phytoplanktonic Community Structure and Production in Relation to Environmental Factors of the Southwest Coastal Waters of Bangladesh

Md. Mahfuzur Rahman Shah
Bangladesh Fisheries Research Institute, Brackishwater Station, Paikgacha, Khulna 9280, Bangladesh.

Md. Yeamin Hossain
United Graduate school of Agricultural Sciences, Kagoshima University,1-21-24 Korimoto, Kagoshima 890-0065, Japan.

Momtaz Begum
Bangladesh Fisheries Research Institute, Brackishwater Station, Paikgacha, Khulna 9280, Bangladesh.

Zoarder Faruque Ahmed
Department of Fisheries Management, Faculty of Fisheries, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Jun Ohtomi
Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0065, Japan.

Mohammad Mustafizur Rahman
Aquaculture Research Team, East Sea Fisheries Research Institute, 30-6, Dongduk, Yongok, Gangnung 210-861, Republic of Korea.

Md. Jahangir Alam
Bangladesh Fisheries Research Institute, Brackishwater Station, Paikgacha, Khulna 9280, Bangladesh.

Md. Amirul Islam
Bangladesh Fisheries Research Institute, Brackishwater Station, Paikgacha, Khulna 9280, Bangladesh.

Bernerd Fulanda
Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0065, Japan.

Abstract/ Executive Summary:

The present study was carried out to monitor the plankton community structure and productivity, its diurnal and seasonal variations and the influence of physico-chemical factors in the Shibsha River of the southwest coast of Bangladesh from July 2004 to June 2005. A total of 31 phytoplankton species were identified; 17 belong to Bacillariophyceae, seven to Cyanophyceae, five to Chlorophyceae and two to Dinophyceae. Bacillariophyceae appeared to be the dominant group in terms of total species and cell numbers during the period studied. The over all phytoplankton production was significantly (p< 0.05) higher in June (175.8x10³ cells L^-1) and lower in September (12.0x10³ cells L^-1) attributed to low temperature. Phytoplankton diversity declined to the lowest level in winter and there was a positive correlation with water temperature. The number of phytoplankton species was high (26) in June and quite low (11) in December. Nutrient concentrations including nitrate and phosphate were significantly (p< 0.05) higher in summer, while lower values recorded in winter. The lowest and highest concentration of Nitrate-Nitrogen (NO₃-N) and Phosphate-Phosphorus (PO₄-P) were 0.7, 0.3, 1.9 and 0.9 mg^-1, respectively.

Keywords: Phytoplankton, Production, Southwest coast, Shibsha river

Location: Shibsha River in the southwest coastal portion, Paikgacha, Khulna, Bangladesh.

Start Date: 00-07-2004

End Date: 00-06-2005

Program Area: Crop-Soil-Water Management

Commodity: Water quality

Objectives:

To monitor the plankton community structure and productivity, its diurnal and seasonal variations and the influence of physico- chemical factors in the Shibsha River of the southwest coast of Bangladesh.

Methodology:

The study was carried out over a period of 12 months from July 2004 to June 2005, at latitude 22° 25´ N and 89° 20´ E. Sampling was done from one selected station at the Shibbari ferry stand point (near Paikgacha town) of the main stream of the Shibsha River in the southwest coastal portion, Paikgacha, Khulna, Bangladesh. Three sub-samples in each day were collected on monthly intervals. Water quality parameters and sampling for plankton analyzes was done once a month between 09.00-1.00 h from specific points of the river at a depth of 20 cm below the surface. A mercury thermometer was used to measure both water and air temperature (°C), while salinity (psu) was measured with a Hand Refractometer. Nitrate-nitrogen (NO₃-N) and phosphate-phosphorus (PO₄-P) concentrations were measured in the laboratory by HACH Kit (DR 2010). For qualitative plankton study, a plankton net was towed for 1 min at a speed of approximately 1 m sec^-1. From the net the collected samples were drained in a polyethylene bottle and preserved with 5% buffered formalin in Brackishwater. For quantitative study a known volume (100 L) of sub-surface water was passed through a plankton net (mesh 25 μm) and the concentrate collected from the bucket and preserved in 5% buffered formalin in brackishwater. The quantitative estimation of phytoplankton was done by Sedgewick-Rafter counting chamber (S-R cell) method using an Olympus binocular microscope. For species identification, a sample was gently shaken to resuspend all materials. It was allowed to settle for a minute and then four drops were removed from the middle of the same sample and placed on a glass slide. A cover slip was placed on the slide and the entire slide was scanned for the species present. Then, the plankton were then identified up to the genus level and enumerated. The mean number of plankton was recorded and expressed numerically per liter of water of the river. The statistical analysis of different physico-chemical and plankton parameters were carried out using one-way ANOVA and any difference at 5% level of significance using the statistical package of Statgraphics Version 7, while the Microsoft exell® 2003 was used to plot graphs for decimination of the results.

Source of Information: Journal of Fisheries and Aquatic Science, 3(2): 102-113, 2008, ISSN 1816-4927.

Article Link (Online Journal): DOI: 10.3923/jfas.2008.102.113, URL: http://scialert.net/abstract/?doi=jfas.2008.102.113

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The over all phytoplankton production was significantly (p< 0.05) higher in June (175.8x10³ cells L^-1) and lower in September (12.0x10³ cells L^-1) attributed to low temperature. Phytoplankton diversity declined to the lowest level in winter and there was a positive correlation with water temperature. The number of phytoplankton species was high (26) in June and quite low (11) in December. Nutrient concentrations including nitrate and phosphate were significantly (p< 0.05) higher in summer, while lower values recorded in winter. The lowest and highest concentration of Nitrate-Nitrogen (NO₃-N) and Phosphate-Phosphorus (PO₄-P) were 0.7, 0.3, 1.9 and 0.9 mg^-1, respectively.

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