The composition and heterogeneity of the rich and diverse rotifers (Rotifera: Eurotatoria) of the floodplain lakes (beels) of the Majuli River Island, Assam State (Northeast India)

The tropical and subtropical floodplain lakes are hypothesized as one of the globally interesting rotifer rich ecosystems. Our study indicating the biodiverse Rotifera of ten ‘slightly acidic to circum-neutral, moderately hard-water and de-mineralized’ tropical floodplain lakes (beels) of the Majuli River Island of the Brahmaputra river basin of northeast India mendorses this hypothesis. Total richness, the richness of important families and community similarities affirm heterogeneity mof the rotifer species composition amongst the beels. The species richness registers significant spatio-temporal variations with seasonal differences amongst the beels and individually in each beel, and lacks significant influence of the recorded abiotic factors. The constellations of 76-81 species in three beels during winter and 76 species in one beel during pre-monsoon are noteworthy instances of ‘Rotifera paradox’. The rotifer fauna of the Majuli beels registers affinity with Southeast Asian and Oriental faunas, records several species of the regional distribution interest and exhibits the littoral-periphytic nature, while application of Q B/T and Q L/B quotients depicts limitations. This study merits ecological diversity interest for Rotifera vis-avis the floodplain lakes of India and elsewhere from the tropics and subtropics, and assumes biodiversity conservation importance due to threat of extinction of the Majuli – an alluvial floodplain of the Brahmaputra basin.