DIVERSITY AND SEASONAL VARIATIONS OF ZOOPLANKTON COMMUNITY IN KUNIGAL TANK, TUMKUR DISTRICT, KARNATAKA

The limnological study is a pre-requisite in any aquatic system to evaluate its potentialities, to understand the realities between various water levels and food networks. Smaller water bodies like ponds, tanks are the important components of the landscape, are seriously threatened by climate change, eutrophication, and other anthropogenic activities Recently, Aquaculture is fast growing in many parts of India and in the world. Zooplanktons are the important component of the biotic habitat that influence the functional aspects and plays a key role in the food chain, nutrient recycling, and energy flow in the aquatic ecosystem. Zooplanktons are controlled by many factors, such as physico-chemical parameters, trophic status, pollution impact, and all kinds of interactions between biological communities. Members of the zooplankton's community are important for their role in energy transfer in trophic dynamics and water ecosystems. They provide food to fish in freshwater ponds and play a key role in lakes for fish production. Zooplankton diversity is one of the most important ecological parameters in water quality assessment. They are very sensitive to environmental changes and are therefore considered to be the potential indicators of water quality. The present investigation aims to study the zooplankton diversity for a period of two years from February 2014 to January 2016 in Kunigal tank to assess the species composition and seasonal variations of this faunal group. Diversity indices such as Shannon-Weiner Index and Simpson Index were calculated. On monthly basis, the water samples were collected from five sampling sites between 7 am to 9 am. 50 liters of water sample were collected, filtered through 60μm mesh size plankton net. The concentrated water sample was fixed and preserved in 4% formalin, one ml concentrated sample was transferred into Sedge-wick Rafter cell and counted under Olympus binocular microscope. Sample preserved in Lugol’s solution was centrifuged, sample from pellet was observed under digital microscope and planktons were photographed. The results revealed the occurrence of 25 species of zooplanktons belonging to four groups - Rotifera, Cladocera, Copepoda and Ostracoda. Rotifera is represented by 10 species belonging to 6 genera, Cladocera- 8 species belonging to 6 genera, Copepoda -5 species belonging to 5 genera and Ostracoda - 2 species belonging to 2 genera. Rotifera is dominant followed by Cladocera, Copepoda and Ostracoda species. The percentage composition of zooplankton species was found as Rotifera > Cladocera > Copepoda > Ostracoda. Shannon-Weiner Index value of zooplanktons ranged between 2.0 - 3.0 and Simpson Index values between 0 and 1. Temperature was the main factor in the appearance and abundance of Rotifer species. Water temperature, dissolved oxygen, turbidity play an important role in controlling the diversity and density of Cladocerans. High population density of Copepoda during summer may be due to favourable temperature and availability of food. Maximum population density of Ostracoda during summer season may be due to water quality. Shannon-Weiner Index and Simpson Index values indicated the good diversity with less water pollution of the tank. This help in planning of successful fisheries management and to improve the productivity of the tank.