Zooplankton populations of tropical freshwater bodies depend on the primary productivity and physico-chemical parameters.Copepods and cladocerans constitute the dominant groups of freshwater habitat. They inhabit the ponds, lake, rivers and reservoirs and reported to occur more abundantly in ponds and lakes than in rivers (Reid, 1986; Raghunathan, 1983;Sharma, 1991). Some genera of copepods and cladocerans are cosmopolitan in distribution, while others are restricted to some continents (Brooks, 1959;Williamson, 1991). Depth of the pond, water transparency, pH and predators determine the distribution and abundance of copepods (Confer et al., 1983; Patalas, 1971). Dussart (1984) reviewed the systematic and distribution of tropical freshwater zooplankton from all over the world.The successions of zooplankton populations depend upon the interspecific and intraspecific interaction and predation potential (Fernando, 1980). There has been some report on the species composition and species diversity of harpacticoid copepod in tropical reef lagoon (Villers & Bodiou, 1996). The freshwater bodies such as ponds, lakes, rivers and reservoirs of Dharmapuri district, Tamil Nadu characterize tropical freshwater ecosystem.The present paper deals with the copepod and cladoceran populations of fifty freshwater bodies with regard to ecological indices of winter and summer populations. MATERIALS AND METHODSZooplankton samples were collected during September, 1999 (winter) and April, 2000 (summer) from fifty freshwater bodies of Dharmapuri District, Tamil Nadu. Samples were collected during early hours of the day (6.00am), using a plankton net made up of bolten silk (mesh size 100µm)During the study period temperature and pH of the water sample were recorded. The samples were preserved in 5% neutral buffer formalin for qualitative analysis and identified following the taxonomic keys provided by Rajendran (1973), Pennak (1978), Tonapi (1980), Barnes (1982), Battish (1992), Maas (1994), Reddy (1994) and, Dussart and Defaye (1995) for copepods and Michael (1973( ), Venkataraman (1983, Sharma and Michael (1987), Raghunathan (1989) and Murugan et al. (1998) for cladocerans. For quantitative analysis, 100L of water sample was filtered through the plankton net and the plankton sample was carefully transferred with out any loss to a plastic container and preserved in 5% neutral buffer formalin.Copepods and cladocerans were enumerated using SedgewickRafter chamber following Santhanam et al. (1989). The data was analyzed for ecological indices such as similarity and dissimilarity, index of dominance, index of diversity, index of evenness and species richness following the methods described by Odum (1983). (Fig. 1-4). RESULTS Copepods May 2004May 2004 DISCUSSION In this study H. viduus and S. (R.) indicus, S. (R.) indicus andT. hyalinus showed similar dissimilarity range in both the seasons, but H. viduus and T. hyalinus showed similar range during summer season, whereas in winter season other copepods showed similar range (0.76-...

Meiofauna standing stocks and community structures were studied at five sandy beaches along the Chennai coast of the

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Some colonies of Porites sp. at Poshitra Reef were spotted with pink swollen nodules. These nodules are termed as a condition called “Porites trematodiasis” which is due to an infection of digenetic trematodes. The temperature fluctuation and anthropogenic pressures are perhaps the reasons.  This situation indicates that if the corals fail to develop disease resistance and thermal tolerance, the reefs along the Indian subcontinent may experience a phase shift in community structure, which could impact fisheries.

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