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Seasonal Dynamics in the Occurrence and Abundance of Pseudo-nitzschia Species in the Moheshkhali Channel of the Bay of Bengal, Bangladesh

M.A. S. Jewel
Department of Fisheries and Aquaculture, Rajshahi University, Rajshahi, Bangladesh

S. Khan
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M. M. Haque
Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Occurrence and abundance of Pseudo-nitzschia spp. at the momh of the Maheshkhali .channel ofthe Bay of Bengal, Bangladesh were studied. Plankton and water samples were collected monthly from the sub-surface water during high tide at daytime from June 2000 to May 2001. Four species of Pseudo-nitzschia, namely P. pungens, P. pseudodelicarissima., P. delicatissima and P. australis were identified and among them the first three were most commonly encountered and they varied seasonally. Pseudonitzschia delicatissima was the dominant species during the autumn and winter months, whereas P. pungens was dominant during the summer and spring months. Pseudonitzschia pseudodelicatissima exhibited its highest abundance level during the summer. Surface water temperature, salinity, nitrate-nitrogen (N0₃-N) and phosphate-phosphorus (P0₄-P) were recorded and their relationship with the occurrence and abundance of Pseudo-nitzschia species were studied. At the mouth of the Maheshkhali channel, Pseudo-nitzschia cell density was highest in late autumn (November) when highest salinity (35%o) and P0₄-P (3.2 mg/l) concentrations and low temperature (23 °C) were recorded.

Keywords: Pseudo-nitzschia, Maheshkhali channel, Bay of Bengal

Location: Moheshkhali channel of the Bay of Bengal, Bangladesh

Start Date: 00-06-2000

End Date: 00-05-2001

Program Area: Resource Development and Management

Commodity: Aquatic animal

Objectives:

To determine the effects of environmental factors on the occurrence and abundance of Pseudo-nitzschia spp. in a restricted area of the Maheshkhali channel of the Bay of Bengal.

Methodology:

Monthly plankton samples were collected for 12 months from June 2000 to May 2001 during daytime at high tide using a 15 Micro meter mesh plankton net at a fixed station near the mouth of the Maheshkhali channel of the Bay of Bengal, Cox's Bazar, Bangladesh. For qualitative plankton study, the plankton net was towed just under the water surface for one minute at a speed of approximately 1 m/s. From the net, the collected samples were drained in a polyethylene botde and were preserved with 5% buffered formalin in sea water. For quantitative study, a known volume (100 lines) of sub-surface water was passed through a plankton net (mesh 15 Micro meter) and the concentrate was collected from the bucket and preserved in 5% buffered formalin in sea water. The quantitative estimation of phytoplankton was done by Sedgewick-Rafter counting chamber (S-R cell) using an Olympus phase-contrast microscope. Surface water temperature and salinity were determined on the spot using a Celsius thermometer and a hand refractometer, respectively. Nitrate-nitrogen (N0₃-N) and phosphate-phosphorus (P0₄-P) concentrations were measured in the laboratory by HACH kit (DR/2010, a direct reading spectrophotometer) using high range chemicals (N0₃-N by NitraVer 5 nitrate reagent powder pillows for 25 ml sample and P0₄-P by PhosVer 3 phosphate reagent powder piHows for 25 ml sample). For species identification, a sample was gently shaken to resuspend all the materials and it was allowed to settle for one minute. Then three drops were removed from the middle of the 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. Observations were made using an Olympus phase-contrast microscope at 100 to 400 X with bright field illumination. Seasons were divided as follows: summer (June through August), autumn (September through November), winter (December through February) and spring (March through May).

Source of Information: Bangladesh J. Fish. Res., 9(2), 2005: 169-174

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

At the mouth of the Maheshkhali channel, Pseudo-nitzschia cell density was highest in late autumn (November) when highest salinity (35%o) and P0₄-P (3.2 mg/l) concentrations and low temperature (23 °C) were recorded.

Knowledge Management: Journal