Abstract

Zooplankton plays an important role in fresh water ecosystems in transfer of energy at the secondary trophic level in an aquatic ecosystem. They are intermediate link between primary producers viz. phytoplankton with higher trophic level organisms. Zooplanktons are rich in essential amino and fatty acids and provide fish with nutrients and their study is necessary in fisheries and aquaculture and is considered as nature’s water purifiers and respond quickly to the changes in the medium and are used as indicators of overall health of the aquatic ecosystem. Zooplankton is important in understanding the lake dynamics and the results of the study undertaken at Kanjia lake of Nandankanan sanctuary, are discussed in detail.The grab samples were collected from four different sites, enough to accurately represent the whole water body to assess their physical and chemical and biological parameters at monthly intervals in the middle of every month between 9:00- 11:00 am.To minimize the changes in the sample from collection to laboratory analysis, the sample was preserved soon after the collection by 5 % formalin.The preserved samples were brought to the laboratory for qualitative and quantitative analysis. Quantitative studies were made by using Sedgwick rafter cell. Different physicochemical parameters were measured in the field itself by physical methods or by using Systronics P-4 water analysis kit (E-Merck). Zooplanktons density ranged from 52 to 66.25 nL-1with mean ± S.D. (58.765 ± 5.844) during winter season, 90.625 to 127 nL-1 with mean ± S.D. (104.609 ± 15.661) during summer season and 49.375 to 69.312 nL-1 with mean ± S.D. (58.656 ±8.324) during monsoon season.The variations across sites and over seasons were significant.The total densities of zooplankton were found to be maximum during summer and minimum during monsoon season. In the community structure and species diversity, protozoa found to be dominant group followed by rotifera, cladocera, copepoda and astracoda. Average of four years density also found to be minimum during monsoon and maximum during summer. In general higher zooplankton density was much more pronounced during the summer season than the monsoon and winter periods in the lake. During the present investigation, the water samples from four study sites have been analyzed for spatial and temporal distribution in density, diversity and percentage distribution of zooplankton. The study revealed the presence of 30 species, out of which 10 species of Protozoa, 9 species of Rotifera, 4 species of Cladocera, 3 species of Ostracoda, and 4 species Copopoda. The zooplankton assemblage of this lake consists primarily of protozoa followed by Rotifers. In the community structure and species diversity, out of 30 species recorded, the Protozoa were found to be dominant group consisting of 10 species ((33.33%) followed by Rotifera with 9 species (30%), Cladocera with 4 species (13.33%), Copepoda with 4 species (13.33%) and Ostracoda with 3 species(10%). KEY WORDS: KanjiaLake, zooplankton, seasonal variation, physico- chemical parameters.

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