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Post monsoonal phytoplankton diversity and chlorophyll-a distribution in a relation to nutrient concentration around Monpura island of North Bay of Bengal, Bangladesh.

Abstract: Phytoplankton identification of surface water was done around Monpura Island (22° 3’51.31″N to 22°20’52.33″N and 90°54’26.83″E to 91° 0’6.38″E) in the northern tip of Bay of Bengal along with its diversity during the period of post monsoon (October-November). This study found 6 species of Bacillariophyceae i.e. Thalassiosira rotula, Rhizosolenia styliformis, Rhizosolenia hebetate, Eucampia cornuta, Chaetoceros sp., Thalassionema  nitzschioides and 1 species of Mediophyceae i.e Isthmia nervosa. Related chlorophyll-a concentration was also measured by spectrophotometer for having a better concept of relationship with a biological factor i.e. DO and various nutrients i.e. NO2-, NO3-, NH4+, SiO2 and PO43- . The average chlorophyll-a concentration was 0.28 mg L-1. During the whole post monsoon, it showed positive relations with DO, NO2-, NO3- and PO43- and negative relations with NH4+ and SiO2 around that island. Different types of correlation methods clarify these relations among each parameter.  This study hypothesized that NH4+ and SiO2 inhibit the concentration of chlorophyll-a and it increases with the abundance of NO2-, NO3- and PO43-. Due to the river and channel erosion, SiO2 concentration was high; so, the diatoms were identified greatly there. The study observed moderately high DO which is averagely stable during whole post monsoon (Oct-Nov) but about chlorophyll-a, there are some anomalies located around the south part of island. Through rest of the study area, chlorophyll-a fluctuates a little during the study time.

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