The biodiverse zooplankton of Bhereki, Holmari and Ghotonga beels of Majuli River Island, the Brahmaputra river basin of upper Assam, northeast India (NEI) revealed total richness of 141 (118±8) species and thus suggested habitat diversity of these floodplain wetlands. Low community similarities, monthly richness variations and the cluster groupings affirmed heterogeneity of zooplankton species composition. Zooplankton formed the dominant component of net plankton in Ghotonga beel and showed sub-dominance in Bhereki and Holmari beels. Rotifera > Rhizopoda influenced zooplankton density in Bhereki and Ghotonga beels; Rhizopoda > Rotifera showed importance in Holmari beel; and Copepoda > Cladocera recorded sub-dominance in all beels. Zooplankton is characterized by higher species diversity and equitability, and lower dominance. The richness, abundance and diversity of zooplankton and abundance of the constituent groups followed oscillating monthly variations. While explaining limited influence of individual abiotic factors and low cumulative influence along two axes (vide Canonical Correspondence Analysis), our results suggested that zooplankton are largely generalists in terms of abiotic factors and thus hypothesized importance of factors associated with microhabitat. formalin. These samples were subsequently screened for various zooplankton species and their permanent mounts were made in polyvinyl alcohol-Lactophenol mixture.Monthly quantitative zooplankton samples were also obtained by filtering 25 litres of the lake water through nylobolt plankton net (No. 25). Individual collections were then concentrated to 25 ml each and preserved in 5% formalin. The quantitative enumeration (n/l) was done with the help of a Sedgewick-Rafter counting cell. The zooplankton was identified following the works of [1,[14][15][16][17][18][19]. Quantitative samples were analyzed for abundance of zooplankton. Community similarity (Sørensen's index) and species diversity (Shannon's index) were calculated following [20,21]. ANOVA was used to analyze the significance of temporal variation of the biotic communities. Ecological relationships between abiotic and biotic parameters of Bhereki beel, Holmari beel and Ghotonga beel were determined by simple correlation co-efficient (r 1, r 2 and r 3, respectively); P values were calculated and their significance was ascertained after the use of Bonferroni correction. The canonical correspondence analysis (XLSTAT 2014) was done to analyse cumulative influence of seventeen abiotic parameters (water temperature, rainfall, pH, specific conductivity, dissolved oxygen, free CO 2 , total alkalinity, total hardness, calcium, magnesium, chloride, dissolved organic matter, total dissolved solids, phosphate, nitrate, sulphate and silicate) on the zooplankton assemblages.

Abstract. The plankton and semi-plankton samples collected from four floodplain lakes (beels) of Barpeta district of lower Brahmaputra river basin, Assam state, northeastern India (NEI) revealed eighteen rotifer species of biodiversity and biogeographic interest belonging to five families and six genera. One species is new to the Indian Rotifera and one species is new to Assam. Our collections are characterized by two Australasian elements, five Oriental endemics, seven paleotropical species, and one cosmo (sub) tropical species. Nine species, restricted to date to NEI, are examples of regional distribution importance in India while six species depicted disjunct distribution in the country. Interestingly, seven species are categorized as Eastern hemisphere elements. All the taxa are illustrated to warrant validation as an increasing magnitude of 'unverifiable records' is a serious impediment for the progress of rotifer biodiversity in India.

Microcrustacea of Loktak Lake (collected during Nov. 2002-Oct. 2004) reveal 57 species and show qualitative dominance of Cladocera (51 species). They indicate monthly richness ranging between 33±6 and 32±6 species, record 51.7-82.3 and 53.6-90.0% community similarities during two years respectively, and follow trimodal annual patterns with peaks during winter. The microcrustaceans (112±17 and 124±13 n/l) form an important quantitative component (45.7±4.9 and 43.3±3.7 %) of zooplankton and show broadly trimodal annual patterns with peak abundance during winter. Cladocera > Copepoda mainly contribute to their quantitative variations. ANOVA registers significant monthly variations of microcrustacea richness and significant annual and monthly variations of their abundance. Richness is positively correlated with dissolved oxygen and is negatively correlated with rainfall, hardness, chloride and total dissolved solids while abundance is negatively correlated with pH only. Multiple regressions indicate higher cumulative effect of 15 abiotic factors on richness and abundance. Our results indicate no definite periodicity of richness and abundance of microcrustacea or their constituent groups during two annual cycles and are characterized by their higher species diversity, higher evenness and lower dominance.