Biodiverse rotifer assemblage (Rotifera： Eurotatoria) of floodplain lakes of the Brahmaputra basin of lower Assam, northeast India： composition and ecosystem diversity

The study aims to ascertain the hypothesis on the rich rotifer biodiversity of the floodplain lakes(beels) of the Brahmaputra river basin and to use these metazoans to assess trophic status or to characterize habitat variations of wetlands. The plankton samples collected from four beels of lower Assam revealed 160 Rotifera species belonging to 35 genera and 19 families. The richness is of biodiversity value as ~38.0% and ~57.0% of the rotifer species known till date from India and northeast India(NEI), respectively. One species each is new to the Oriental region and NEI, and three species are new to Assam; 23 species merit global biogeography interest and several exhibit distribution values in the Indian sub-region. The diverse Lecanidae > Brachionidae > Lepadellidae > Trichocercidae and speciose littoral-periphytic L ecane > Lepadella > Trichocerca, and richness of Brachionus spp. following removal of aquatic macrophytes are noteworthy. Overall rotifer composition showed homogeneity amongst beels while lower monthly richness and community similarities affirmed heterogeneity within individual beels. We propose L/B quotient based on L ecane : Brachionus species ratios to characterize habitat variations of the sampled wetlands. Sláde?ek's B/T quotient based on B rachionus : T richocerca species ratios affirmed general 'meso-trophic' status of diff erent beels. Our results provided little insight on the influence of individual abiotic factors but the canonical correspondence analyses asserted higher cumulative influence of ten abiotic parameters on Rotifera richness in each beel.

Phytoplankton Diversity of a Demineralized Urban Wetland of Meghalaya State of Northeast India:The Spatio-temporal Variations and the Role of Abiotic Factors

The authors analyze phytoplankton diversity of a small urban wetland of Meghalaya to assess biodiversity and limnology interest of small water bodies.This“slightly acidic-circumneutral,demineralized and soft water”subtropical wetland reveals diverse phytoplankton(64 species),indicates high desmid richness and highlights the speciose littoral constellations of up to 55-58 species per sample.Phytoplankton comprises dominant quantitative component of net plankton and registers Charophyta dominance;Chlorophyta>Bacillariophyta>Dinozoa>Chrysophyta>Cyanobacteria depict sub-dominance,and Euglenozoa and Cryptophyta show poor abundance at the littoral and semi-limnetic regions.The richness of phytoplankton and abundance of phytoplankton,Charophyta,Chlorophyta,Dinozoa,Chrysophyta and Cyanobacteria follow bimodal spatio-temporal variations.Closterium,Cosmarium,Staurastrum,Micrasterias,Netrium,Staurodesmus and Scenedesmus are notable genera,and 14 species collectively influence phytoplankton abundance.Phytoplankton registers high species diversity,lower dominance and high evenness.Amongst 15 abiotic factors,only the rainfall and sulphate exert notable influence individually,while the canonical correspondence analysis registers lower cumulative influence of the selected 10 factors on the littoral and semi-limnetic phytoplankton assemblages.This study merits interest for neglected biodiversity and ecology of small aquatic biotopes of India and urban wetlands in particular.

Zooplankton Diversity of a Soft-water and Highly De-mineralized Reservoir of Meghalaya(Northeast India):The Spatio-temporal Variations and Influence of Abiotic Factors

Hydrobiological survey of a‘soft-water’and‘highly de-mineralized’reservoir of Meghalaya state of northeast India is undertaken to analyze zooplankton diversity with reference to the spatio-temporal variations and influence of abiotic factors.The littoral and limnetic zooplankton assemblages of this subtropical reservoir without aquatic vegetation reveal total 36 species,and record lower abundance,quantitative dominance of Rotifera,sub-dominance of Cladocera and Copepoda and moderate species diversity.Keratella cochlearis,Bosmina longirostris,Polyarthra vulgaris,Mesocyclops leuckarti,Conochilus unicornis and Asplanchna priodonta influence abundance,species diversity,dominance and equitability of zooplankton.We report differential spatial influence of individual abiotic factors with the relatively more importance at the limnetic region,and the canonical correspondence analysis registers 72.5%and 78.8%cumulative influence of 10 abiotic factors on the littoral and limnetic assemblages,respectively.The spatial differences of various diversity aspects and the influence of abiotic factors suggest habitat heterogeneity amongst the two regions.This study is a useful contribution to zooplankton diversity of the subtropical environs,and soft and de-mineralized waters in particular.Our results mark a distinct contrast to the lowest richness and abundance of zooplankton noted from India vide the preliminary 1990-91 survey of this reservoir.