THE SEASONAL CYCLE OF THE PHYTOPLANKTON IN THE COASTAL WATERS OF CHATTOGRAM

Abstract

The present investigation studied the seasonal variation of different physico-chemical parameters and phytoplankton composition from the northern BoB. Water samples were collected during monsoon and winter from the coastal waters of Chattogram (Bashbaria and Patenga). Surface water temperatures (ºC) varied from 25.4 to 32.2 whereas salinity values (psu) varied from 3.7 to 21.3 and the pH ranged between 6.7 and 7.6. Total dissolved solids (g/L) and total suspended solids (g/L) content varied from 2.82 to 22.3 and 0.55 to 0.94 respectively. The electro-conductivity (mS/cm) of all samples of surface water ranged between 5.6 and 44.7. The ranges of inorganic nutrients (μg/L) viz., nitrite, phosphate, silicate and ammonia were as 0.34-2.13; 0.55-0.93; 87.75-422.64 and 212-284.7 respectively. The ranges of alkalinity (ppm) and Chlorophyll-a concentration (μg/L) were 89.5-130 and 0.27-0.71 in turn. Significant seasonal variations found between two seasons (p<0.05) except for total suspended solids. During the study period total 7 genera of dominant phytoplakton under 3 classes were identified of which 4 genera under Bacillariophyta, 1 genera under Dinophyceae, and 2 genera under Coscinodiscophyceae. Identified dominant genera were Thalassiothrix, Chaetocerus, Skeletonema, Cyclotella, Cerataulina, Coscinodiscus and Ditylum. The maximum abundance of phytoplankton were 9.6 × 102 cells /L at station 1 (Bashbaria coast) and 13.4 × 102 cells/L at station 2 (Potenga coast) during monsoon. Among the phytoplankton samples, Bacillariophyceae was the most dominant class. The percentage of Bacillariophyta to the total phytoplankton community in two seasons varied between 45% and 47% in station 1 and 49.43% and 36.51% in station 2. Among the identified factors chlorophyll-a, water temperature, nitrite, and ammonia had a positive influence on phytoplankton abundance. Therefore, the findings of this study would be helpful for policymakers in improving management practices for maintaining water quality and conserving the phytoplankton population.