Diversity of zooplankton in a tropical floodplain lake of the Brahmaputra river basin, Assam (Northeast India)

The zooplankton diversity of a floodplain lake of the Brahmaputra river basin of lower Assam is analyzed on the bases of net plankton samples collected from the littoral (station 1) and semi-limnetic (station 2) regions during January–December 2010. The species-rich zooplankton (143 species) hypothesized environmental heterogeneity of this wetland. They showed high monthly richness (81 ± 11 and 72 ± 11 species) and recorded 44.7–79.3% and 46.7–89.7% community similarities at two sampling stations, respectively. Zooplankton formed 55.5 ± 10.9 % and 63.9 ± 9.6 % of net plankton abundance. Rotifera > Cladocera mainly influenced their richness and density variations. Copepoda is a sub-dominant quantitative group while Mesocyclops spp., Asplanchna priodonta, Chydorus sphaericus, Bosmina longirostris and Sinantherina socialis are relatively important taxa. High species diversity and low densities of majority of species are hypothesized to fine niche portioning amongst different species in combination with high micro- and macro-scale habitat heterogeneity. The zooplankton is characterized by high equitability and low dominance. Individual abiotic factors recorded limited influence on richness and abundance. Canonical correspondence analysis with ten abiotic factors explained 56.0 % and 55.8 % cumulative variance of zooplankton assemblages along axis 1 and 2. The CCA affirmed micro-environmental differences between the sampling stations.