Abstract
Phytoplankton communities of Loktak Lake (a Ramsar site), studied during November 2002-October 2004, reveal the occurrence of 75 and 71 species, indicate monthly richness ranging between 47� plus or minus 6 and 49� plus or minus 3 species and record 50.0-83.2 and 64.5-84.0 % community similarities during two annual cycles respectively. Chlorophyta (33� plus or minus 5 and 35� plus or minus 5 species) show qualitative dominance and importance of Closterium > Cosmarium > Staurastrum > Micrasterias > Gonatozygon species. Phytoplankton (206� plus or minus 58 and 220� plus or minus 53 n/l) comprise between 45.1� plus or minus 6.5 and 42.9� plus or minus 5.8 % of net plankton abundance, indicate trimodal annual patterns and record peak abundance during winter. Chlorophyta (111� plus or minus 20 and 119� plus or minus 15 n/l), the dominant quantitative component, indicate winter peaks; Closterium > Staurastrum > Gonatozygon > Micrasterias species contribute significantly to their abundance. Ceratium hirudinella (43� plus or minus 52 and 39� plus or minus 37 n/l) is the sole important individual species of phytoplankton. Dinophyta > Bacillariophyta are sub-dominant groups and Euglenophyta > Cyanophyta > Chrysophyta show very low densities. Phytoplankton communities are characterized by higher species diversity, higher evenness and lower dominance. Abiotic factors register limited influence on richness and abundance of phytoplankton and on abundance of constituent groups. Multiple regression indicates relatively lower influence of fifteen abiotic factors on richness of phytoplankton and higher cumulative influence on abundance of phytoplankton, Chlorophyta, Dinophyta and Bacillariophyta.
Highlights
The floodplain lakes cover a water spread area of about 0.12 million ha in northeastern India, are mainly located in the states of Assam and Manipur and exhibit significant fishery production potential (Sugunan 1997)
The abiotic factors differ from Deepor Beel (Sharma in press), distinctly in the recorded ranges of pH, alkalinity and hardness
Total richness is distinctly higher than only 33 species examined earlier in an unpublished report (Bhatia 1979) from this wetland as well as than 59 species reported from Deepor Beel (Sharma in press)
Summary
The floodplain lakes cover a water spread area of about 0.12 million ha in northeastern India, are mainly located in the states of Assam and Manipur and exhibit significant fishery production potential (Sugunan 1997). Observations were made on monthly variations in richness, abundance of phytoplankton, their constituent groups, community similarities, species diversity, dominance and evenness for two annual cycles. This generalization concurs with the authors earlier remarks in two floodplain lakes of Assam (Sharma 2004, in press) while Loktak phytoplankton reflect higher range of richness variations.
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