Diversity, Distribution and Abundance of Bivalves in Vembanad Backwaters – the largest Ramsar wetland in South India

Present study aimed to investigate the spatial and temporal variability in the diversity, distribution and abundance of bivalves in the largest Ramsar wetland in South India, the Vembanad backwaters. Monthly sampling was carried out at 12 stations from the spreading across the northern, middle and southern regions of the backwater. A total of 20 species of bivalves, belonging to 17 genera under 9 families were recorded during the study, based on which an updated taxonomic checklist including the IUCN conservation status was compiled. Venerida, was the dominant Order (30%) comprising 2 families and 6 species followed by Ostreida (15%), Arcida (15%), Mytilidae (10%), Cardiida (10%) and Pectinida (10%). Order Myida and Unioniidae together contributed only < 5%, with a single species represented from each Order viz., Martesia striata and Lamellidens marginalis , respectively. Higher number of species (16–19 species) in the middle estuarine region. Dominance of single species, Villoritta cyprinoides recorded in the Southern (99%) as well as in the northern region. Mytella strigata , a fouling invasive bivalve species was recorded from middle and northern regions of Vembanad backwaters; Results of present study indicate that the V. cyprinoides occupied all the parts of Vembanad backwaters during all the seasons except in the estuarine region. its abundance was relatively high during the premonsoon, 51% in the middle region and 35% in the northern region. The study suggests prominent spatial variability in the distribution pattern of bivalves in Vembanad backwaters and is based on the prevailing environmental conditions.