Ecosystem diversity of Cladocera (Crustacea: Branchiopoda) of the floodplain lakes of Majuli River Island, the Brahmaputra river basin, northeast India

Plankton and semi-plankton samples collected from twelve floodplain lakes (beels) of Majuli River Island of the Brahmaputra river basin, Upper Assam reveal rich Cladocera assemblage of 48 species belonging to 32 genera and 7 families. This report assumes biodiversity value as ~65.0% and ~37.0% of the species, and ~78.0% and ~72.0 of genera of the taxon known from Assam state of northeast India (NEI) and India, respectively. Picripleuroxus quasidenticulatus (Smirnov) is a new record from the Indian sub-region. Biogeographically important elements include one Australasian, three Indo-Chinese and two Oriental species. Total cladoceran richness in individual beels ranged between 16-38 (26 ± 6) species while monthly and seasonal richness in six beels each varied between 8 ± 3-13 ± 3 species and 11 ± 4-17 ± 3 species, respectively and showed lack of any pattern of temporal variations. The community similarities (40.1-86.5% vide Sí¸rensen's index) and the hierarchical cluster analysis affirm heterogeneity in Cladocera composition in different beels. Individual abiotic factors indicated insignificant influence on richness except for significant positive correlation with alkalinity only in Khorkhoria beel.