The paper deals with the spatial diversity of surface zooplankton in relevance with water quality parameters (water temperature, pH, salinity, turbidity, transparency, dissolved oxygen, biological oxygen demand, chemical oxygen demand, nutrients and chlorophyll pigments - a, b and c) in six stations of the lower stretch of the Hugli estuary, Sundarban, northeastern part of the Bay of Bengal, India. The work has been undertaken for a better understanding of its ecological characteristics in terms of secondary production. Copepods were the most dominant group consisting of 27 species followed by chaetognaths, lucifers, hydromedusae and ctenophores as holoplankters. They constituted the bulk of the biomass sharing 43.13 to 96.55% of the total zooplankton. Correlation matrix showed interesting relationship among the major copepods and also between the water quality parameters, total zooplankton and copepods. Copepods of the low saline upstream assemblage showed a decrease in abundance. The scarcity of the mature chaetognath Sagitta bedoti might be attributed to their presence in the deeper layers. Spatial heterogeneity of zooplankton distribution, especially the copepods, was pronounced revealing different biological characteristics of the wetland.
Zooplankton plays an important role as secondary producers in coastal and marine ecosystems, representing an important link between phytoplankton, microzooplankton and higher trophic levels such as fish. A correlative study on zooplankton distribution, their intensity and abundance in relation to water quality parameters is necessary for a correct understanding of the fishery resources. This is particularly true for estuarine environments because they are extremely dynamic and heterogeneous ecosystems, subject to strong fluctuations of biotic and abiotic factors. Therefore, estuarine ecosystems are of particular interest for studying zooplankton population dynamics. The existing information on zooplankton in a vast tropical estuary like that of River Ganges (Hughli) was rather scarce and over two decades old (Datta et al., 1954; Saha et al., 1975; Bhunia 1979; Sarkar et al., 1984a, b and 1985a, b, c, d). Hence, the present investigation has been undertaken to document a comprehensive account of the spatial distribution of zooplankton in relation to prevailing physicochemical features in the Sundarban mangrove estuarine complex, a dynamic and heterogeneous ecotone formed at the confluence of the Hugli river and the Bay of Bengal. |
