Abstract

Molluscan diversity, seasonal variations and their correlation with the physico-chemical characteristics of Ramsagar reservoir has been done during March, 2003 to April, 2005. A total of 13 species of molluscs were recorded in the reservoir. Out of which Melania (Plotia) scabra, M. scabra var elegans, Melania striatella and Faunus ater belong to family Melaniidae, Vivipara dissimilis to family Viviparidae, Zootecus chion and Opeas gracile to family Subulinidae, Planorbis (Indoplanorbis) exustus, Anisus (Gyraulus) convexiusculus to family Planorbidae, Lymnaea (Pseudosuccinea) acuminata, L. luteola, L. pinguis to family Lymneidae and Lamellidens corrianus to family Unionidae. The dominant class, Gastropoda was represented by 12 species, which were observed throughout the year. Amongst the Gastropoda Vivipara dissimilis was most dominant species in the reservoir. The density of Gastropods ranged from 48 (monsoon) org/m2 to 251 org/m2 (summer). Class Pelecypoda, represented by only a single (Lamellidens corrianus), had its minimum population (3 org/m2) in monsoon and maximum population (22 org/m2) in summer. The physico-chemical characteristics of water suggest that the Ramsagar reservoir is a mesotrophic water body (Garg et al., 2008). The values of coefficient of correlation (r) indicate that there is a moderate positive correlation between the gastropods and electrical conductivity, pH, total alkalinity, phosphates, sodium and potassium, while the pelecypods are positively correlated with electrical conductivity, total alkalinity, chlorides, calcium, nitrate-nitrogen, phosphates and potassium. A moderate negative correlation exists between molluscs population with free carbon dioxide in water. 

Key words: Molluscan diversity, correlation coefficient, Ramsagar reservoir, water quality.