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Lakes, Rivers and Reservoirs are most important water resources with multiple human utilization and
ecological relevance. Parambikulam Dam is an embankment dam on the Parambikulam River flowing
through Western Ghats and located in the Palghat district of Kerala with a reservoir area of 21.22 km2
and 69,165×1000 cu.mt. capacity. The present study focuses on the seasonal variation, hydrobiology and
biodiversity of phytoplankton of the Parambikulam reservoir during 2009-11. A total of 89 taxa of
phytoplankton were recorded during the study. They belong to five different classes, viz Chlorophyceae,
Desmidiaceae, Bacillariophyceae, Cyanophyceae and Euglenophyceae. Bacillariophyceae was the
dominant group with 42 taxa followed by Desmidiaceae with 26 taxa. Members of Euglenophyceae were
not recorded during monsoon seasons. The dominant genera were Pinnularia and Navicula from
Bacillariophyceae and Closterium and Cosmarium from Desmidiaceae. Shannon diversity index and
Margalef’s Species richness was found to be highest during post-monsoon season (H’=6.09; d=11.41)
and lowest during monsoon seasons (H’=3.8; d=3.4), while average taxonomic distinctness was slightly
higher in pre-monsoon (Δ+=69.30) than post-monsoon (Δ+=69.10) and lowest during monsoon
(Δ+=65.00). Variation in taxonomic distinctness was highest during post monsoon (Ʌ+=417) and lowest
during pre monsoon (Ʌ+ =347). Fluctuations of the hydrological variables such as pH, DO, nitrate,
phosphate, silicate, calcium and chloride were also recorded. The result provides a primary
documentation of the microalgae and basic understanding of the trophic status of the reservoir.
Keywords- Phytoplankton, Western Ghats, Hydrobiology, Biodiversity, Parambikulam Dam.