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Nongmahir reservoir of Meghalaya state of northeast India (NEI), sampled at the littoral and limnetic regions, revealed fairly biodiverse zooplankton of total 56 species with peak consortium (52 species) in January collection from the littoral region. The richness indicated spatial monthly variations and heterogeneity at the two regions mainly influenced by Rotifera. The ‘soft and de-mineralized waters’ resulted in low zooplankton abundance. Copepoda > Rotifera with Cyclopidae > Brachionidae influenced zooplankton, and Mesocyclops leuckarti > Keratella cochlearis > Ascomorpha ovalis > Microcyclops hyalinus are notable species at the littoral region. The limnetic region recorded Rotifera dominance, and importance of Brachionidae > Cyclopidae and K. cochlearis > Conochilus unicornis >M. leuckarti >A. ovalis > Asplanchna priodonta > Polyarthra vulgaris. Zooplankton recorded moderate species diversity and notable differences of evenness and dominance. The spatial monthly differences of richness, abundance and diversity indices of zooplankton, and importance of notable taxa are hypothesised to habitat heterogeneity of the two regions. Our results also indicated limited and differential influence of individual abiotic factors on zooplankton taxa, while the canonical correspondence analysis registered high cumulative influence of 10 abiotic factors on the littoral (80.62%) and limnetic (74.79%) assemblages along axis 1 and 2. This study highlighted distinct temporal variations of different diversity parameters than our preliminary survey of June 1995–May 1996.

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.

This study on zooplankton diversity from the state of Mizoram of northeast India, based on plankton samples collected from Khawiva reservoir during November 2005-October 2007, recorded a total of 46 species. Zooplankton indicated monthly richness ranging between 19-36 and 25-34 species; registered 52.8-88.9 and 60.0-89.3% community similarities (vide Sørensen’s index); and comprised between 31.2±12.7 and 46.7±11.3% of net plankton abundance during two years, respectively. Copepoda and Rotifera, together, influenced zooplankton abundance. Rhizopoda and Cladocera showed limited importance while Nematoda and Ciliata recorded poor densities. Mesocyclops spp. > Keratella tropica are important taxa. Our results are characterized by moderate species diversity, high evenness and low dominance except in some months. Richness, abundance and species diversity followed no definite patterns of monthly variations. Individual abiotic parameters exerted limited influence on zooplankton richness and abundance, and on abundance of its constituent groups. The canonical correspondence analysis with fifteen abiotic parameters explained high cumulative variance (84.8%) of zooplankton assemblages along axis 1 and 2 with importance of water temperature, rainfall, free carbon dioxide, conductivity and phosphate. Sladecek’s Q B/T quotient and Shannon’s diversity index reflected mesotrophic nature of Khawiva reservoir.

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.

This study analyzed diversity and ecology of planktonic Rotifera of Ghorajan beel, a floodplain lake of the Brahmaputrariver basin of lower Assam region of Northeast India. Plankton samples collected (January–December, 2010) fromlittoral (station 1) and semi-limnetic regions (station 2) of this tropical wetland revealed a fairly rich rotifer fauna (84 and 80species) with distinct variations (range, average ± SD) in monthly richness (35–55, 46±6 and 24–54, 36±5 species) andcommunity similarities (46.6–80.4 and 37.0–95.9 %) at both sampling stations. The richness followed unclear annual patterns.The rotifers mainly contributed (53.3±5.1 and 55.6± 3.6 %) to zooplankton abundance variations and showed high abundancefrom June through November at both stations. Brachionidae > Lecanidae exhibited high number of individuals; Asplanchnidaeand Flosculariidae were also quantitatively important families; specifically, Asplanchna priodonta, Sinantherina socialis, Brachionusfalcatus and Lecane bulla were important species for their abundance. Single abiotic factors exerted a more limited influence on richness than on abundance. Canonical correspondence analysis (CCA) explained 55.6 % and 59.5 % cumulative variance of the rotifer assemblages along axis 1 and 2, respectively; the CCA indicated the importance of transparency and rainfall at station 1, and of transparency, dissolved oxygen and rainfall at station 2. Consequently, the littoral and semi-limnetic stations are characterized by micro-environmental differences.

Plankton samples collected (November, 2002 – October, 2004) from Waithou and Utra pats, two floodplain lakesin Manipur state of northeast India, revealed species rich zooplankton (121 species) with diverse nature of Rotifera (75 species).The individual pats exhibited rich species diversity (110 and 103 species) and high monthly richness (68±7 and 61±8 species)respectively with higher community similarities. Zooplankton formed important quantitative component (56.0±4.3 % and55.1±5.1 %) of net plankton of the two pats; Rotifera dominantly contributed to their abundance while Cladocera > Copepodawere sub-dominant groups. The richness and abundance showed significant variations between pats and between months andfollowed oscillating annual patterns in each pat except for peaks during winter. Zooplankton indicated higher species diversityand evenness, lower dominance, lack of quantitative importance of individual species, low densities and equitable abundance ofthe majority of species in both pats. The richness correlated inversely only with nitrate in Waithou pat and abundance positivelycorrelated with alkalinity only in Utra Pat. Canonical correspondence analysis (CCA) with abiotic factors explained 55.6 % and61.8% cumulative variance of zooplankton assemblages of Waithou and Utra pats respectively along axis 1 and 2.