Rotifera diversity of a floodplain lake of the Brahmaputra river basin of lower Assam, Northeast India

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.