Examining the Diversity and Abundance of Zooplankton across Different Gateways in the South-western Estuary of Bangladesh

The Pasur-Sibsa and Baleshwari River Estuary (PSBE) is the longest estuary located in the southwest part of Bangladesh on the Ganges-Brahmaputra delta which flows into the Bay of Bengal.The study was conducted to investigate the diversity and abundance of the zooplankton from three gateways (S1 station: Pasur river gateway; S2 station: Sibsa river gateway and S3 station: Baleshwari river gateway) in the PSBE from July 2022 to December 2022.Water samples were collected from these gateways using plankton net (55 µm mesh size) and preserved for analyzing in the laboratory.A total of 34 species of zooplankton belonging to 9 orders and 17 families were documented.The dominant orders were Calanoida and Dendrobranchiata, covering 59.52% and 18.20%, respectively.Acartia bilobata was the dominant species, while Sagitta sp. was the inferior species throughout the gateways.The Pasur river estuary gateway showed the highest percentage of abundance, accounting for 36.39% of the total individuals.The study calculated the Shannon-Wiener Diversity Index, Simpson's Dominance Index, Simpson's Index of Diversity, Margalef's Richness Index, and Evenness ranged from 1.33 to 1.43, 0.24 to 0.30, 0.70-0.76,1.11 to 1.21, and 0.74-0.80,respectively.The results showed that the zooplankton composition was rich in the S1 station, which serves as a good indicator of marine productivity like zooplankton.The density of zooplankton in a body of water is indicative of the fish stocking rate.