The present investigation was carried out for two years from March 1988 to February 1990 and focuses on hydrobiological aspects of the southeastern part of the Bangladesh coastal waters in the Bay of Bengal. The hydrological factors were mainly governed by the monsoons and river systems flowing into the Bay. A marked seasonal fluctuation in salinity, dissolved oxygen, water temperature and suspended particles was observed, which is a unique feature of this northeastern coastal part of the Bay of Bengal. During these two years study, the highest salinity was recorded in the dry winter season (33.4 ‰) and the lowest in the monsoon period 8.08 ‰ and was inversely correlated with rainfall. Dissolved oxygen was higher in winter and summer, and lower in the rainmonsoon months, ranging between 3.5 ml/l and 8.9 ml/l; higher values of water temperature were observed throughout the year except in the winter months (range 21°C-32°C). Lower water transparency was recorded during rainmonsoon (25.7 cm) and higher in winter (70 cm). Settling volume of suspended particles varied between 0.01 ml/l and 6.35 ml/l, being highest in the rainy period and lowest in Dry season pH ranged between 7.0 and 9.0 and showed a significant positive correlation with salinity. Effective rainfall being confined to the monsoon months. The bright sunshine occurred from December to April. A year round investigation from March 1988 to February 1989 revealed that phytoplankton abundances on the Kutubdia channel shows strong seasonal variation. The higher abundance of phytoplankton was recorded in autumn, winter and early spring (late September-February) when bright sunshine occurred also. The minimum densities were in summer and during rainy seasons (mid April-August). The peak occurrence of phytoplankton was recorded in ]anuary (3332 cells/l) during the low turbitity period and minimum in August (1295 cells/l). Phytoplankton population was shown to have a significant negative correlation with suspended particles in the four stations in the studied channel (S1,r = -0.887, P<0.1; S2, r = -0.920, P<0.001, S3, r = -0.807, P<0.01, S4, r = -0.920 P<0.001). Phytoplankton was counted in 4 groups. Bacillariophyta was the dominant group and occupied (64.4 %) of the yearly average number. The other constituents were Chlorophyta (18.5 %), Pyrrophyta (9.2 %) and Cyanophyta (7.6 %) respectively. The phytoplankton population of this area was dominated by Skeletonema costatum (21.8 %). Bacillariophyta and Pyrrophyta were shown to have the same seasonal evolution, with the peak of abundance in the postmonsoon (September-January) and the lowest value during monsoon season (April-August). The highest abundance of Cyanophyta in the rainy season was due to river discharge, the minimum of Chlorophyta was recorded in the rainy season when the lowest salinity was recorded. A year round investigation (March 1988-February 1989) on zooplankton with emphasis on commercially important cultivable shrimp postlarvae in the southeastern part of the Bangladesh coastal waters of the Kutubdia channel leads to monthly quantitative estimation of zooplankton under 13 major taxonomic groups. Copepods were the most abundant group and occupied 94.3 %. The other main constituents were chaetognaths (2.5 %), Acetes (1.1 %), Lucifers (0.7 %), crab larvae (0.3 %), molluscs larvae (0.24 %) mysids (0.23 %), Squilla larvae 0.19 % shrimp postlarvae (penaeid and caridean, 0.9% and Fishlarvae 0.17 %. Maximum density of zooplankton was recorded in September (326146.36/100m³) which indicates a seasonal influence on the distribution pattern of the different groups. Hydromedusae, Mysids and Squilla are shown as major indicator group and they represent only <1 % of the zooplankton population. All dominant groups show the same seasonal variation. The zooplankton abundance in the Kutubdia channel could not be significantly correlated with phytoplankton (r = 0.29, P>0.05). Only at station 1, fish larval abundanc |
