Phytoplankton Diversity of a Subtropical Reservoir of Meghalaya State of Northeast India

The littoral and limnetic phytoplankton of 'soft and de-mineralized water' in the Nongmahir reservoir of Meghalaya state of northeast India (NEI) reveal a fairly diverse assemblage of a total of 52 species, depict a higher richness of Chlorophyta and desmids, and record a speciose constellation of 51 species per sample. Phytoplankton form a dominant quantitative component of net plankton and indicate the differential spatial dominance of important groups. Bacillariophyta > Chlorophyta indicate dominance in the littoral region and Chlorophyta records dominance in the limnetic region. Staurastrum spp. > Cosmarium spp. are important in the two regions. Seventeen 'specialist' species collectively contribute to phytoplankton abundance in the littoral (87.9 +/- 6.9%) and limnetic (91.6 +/- 3.3%) regions and the rest depict a 'generalist' nature. Phytoplankton records moderate species diversity and variations of dominance and evenness. The spatial monthly variations of composition, richness, similarities, abundance, diversity indices and influence of individual abiotic factors are hypothesised to differences in habitat heterogeneity amongst the two regions. The CCA registers 78.36 and 78.95% cumulative influence of 10 abiotic factors on the littoral and limnetic phytoplankton assemblages, respectively. Our results highlight distinct temporal variations of diversity parameters in comparison with the preliminary survey of June 1995-May 1996. This study is an important contribution to phytoplankton diversity of the reservoirs of India and the subtropical reservoirs in particular.