Composition, abundance and diversity of macrobenthic fauna in kole paddy fields, vembanad kole wetland, India

Macrobenthic fauna is important in paddy fields (man managed temporary wetlands) due to its significant role in nutrient cycling. Macrobenthos in Maranchery Kole paddy fields, Vembanad Kole wetland, a Ramsar site in Kerala, India was studied during Punja (summer crop season) 2011. Macrbenthos belonged to 3 phyla, 4 classes [Insecta (78%), Oligochaeta (20%), Bivalvia (1%), Crustacean (1%)] and fifteen families. The average benthic abundance was 399±581 ind./m2, showing a decreasing trend from the beginning of the crop season to the end. As paddy plants grow up, shading by paddy plants reduced the sunlight penetration to the bottom of the paddy field thus reducing decomposition rates resulting in decrease in detritus quantity, which lead to decreased abundance as detritus feeders were the predominant group there. Further the growth of paddy plants leads to the increase in paddy root structures thus gradually decreasing habitable area for benthic fauna resulting in decreased abundance as the crop season progressed. No significant correlation emerged between benthic abundance and environmental parameters, Available limited habitable area and agricultural practices might have determined abundance. Further the narrow range of environmental variables (as paddy fields were man managed) also might have resulted in insignificant correlation.