Phytoplankton diversity of Deepor Beel - a Ramsar site in the floodplain of the Brahmaputra River basin, Assam, north-east India

Abstract

Plankton samples collected from two sampling stations (station I and II) of Deepor Beel, a Ramsar site, during November 2002 to October 2003, revealed occurrence of 59 species of phytoplankton belonging to 55 genera with species rich Chlorophyta > Bacillariophyta. They indicated monthly richness varying between 34 - 53 (39±6) species and
36 - 45 (39±3) species, and recorded 39.4 - 87.4% and 52.8 - 79.6% community similarities (vide Sorensen index) at two sampling stations, respectively. Phytoplankton formed 42.1 ± 9.0% and 43.6 ± 8.8% of net plankton abundance at stations I and II, respectively. Chlorophyta > Bacillariophyta influenced quantitative variations; Dinophyta and Cyanophyta were subdominant groups; Chrysophyta and Euglenophyta showed low abundance, while Ceratium hirudinella, Microcystis aeruginosa, Dinobryon sociale, Cosmarium granatum, Closterium sp., Oscillatoria sp. and Spirogyra sp. were important taxa. Phytoplankton recorded high species diversity, high equitability and low dominance. Individual abiotic factors exerted limited influence on richness and abundance of phytoplankton and their constituent groups. The canonical correspondence analysis (CCA) with ten abiotic factors explained 55.3% and 77.9% cumulative variance of phytoplankton along axis
1 and 2 with importance of different factors at two sampling stations, respectively and thus affirmed micro-environmental differences between them.