Abstract
Among the zooplankton, Rotifera comprise an integral part of the food chain and are important link between nanoplankton and carnivorous zooplankton. The diversity of rotifers is indicative of the ecological factors of the water body as they respond more quickly to environmental changes and appear as sensitive indicators of changes of water quality. In this context, species diversity of planktonic rotifers and its community assemblage in Vembanad backwater (Ramsar site) has been carried out from March 2012 to February 2013 from ten selected stations on North and South of the Thanneermukkom barrage. Abiotic and biotic parameters were determined and correlated with rotifer abundance to gain information about the forces that assembles the rotifer community in this dynamic environment. Maximum abundance was observed during monsoon (av. 8934 individual mG3) followed by premonsoon (av.5549 individual mG3) and postmonsoon (av. 4011 individual mG3). During the present study 26 species of the rotifers belonging to 10 families were observed, with maximum abundance of Brachionus sp. (60%). Predominant species were Brachionus rotundiformis (16.4%), B. calyciflorus (6.6%), B. urceolaris (5.5%), B. plicatilis (4.05%), Keratella tropica (3.2%) and Asplanchna sp. (2.2%). Most of the dominant species observed were eurytopic freshwater forms that became less abundant towards downstream (station 8, 9 and 10) with respect to the salinity gradient prevailing in the estuary. Highest Shannon diversity index (4.51) was observed in station 3 (Rani) and lowest (2.73) in station 10 (Aroor). Multivariate Bio-Env (BEST) analysis showed that temperature, conductivity, salinity and phosphate best determined the abundance and distribution of rotifers in the Vembanad estuary. As the trophic status and rotifer assemblages of an ecosystem are very much related, a comprehensive study on the species diversity and community assemblage of rotifers in Vembanad estuary can furnish a valuable integrative index for further ecological assessment and monitoring of estuarine ecosystems.
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