Current Velocity: a Driving Factor for Structuring Zoobenthos Community in a Fluvial System of Indian Himalaya

Study was conducted to determine the impact of current velocity on density and abundance of benthic macroinvertebrate fauna in an Indian Himalayan River, the Ramganga. The samples were collected at 8 different stations from headwater to mouth (S1 to S8) during October 2014 to March 2015. One-time intensive sampling (20 quadrates per station) was performed in the dry-period. The benthic macroinvertebrate samples were collected to all possible current velocities at each station from 7 cm to 55 cm depth. and they were categorized in to 5 categories of current velocity; extreme low (type I, 0–15 cm s–1), low (type II, 15–30 cm s–1), mild (type III, 30–45 cm s–1), moderate (type IV, 45–60 cm s–1) and high (type V, >60 cm s–1). The standard methods were used to collect invertebrate samples and identify at family level. The total mean density of invertebrate fauna decreased from type I (616 ind. × m–2) to type II (358.87 ind. × m–2), and increased to type III (925.25 ind. × m–2), but again decreased to type IV (539.37 ind. × m–2) and type V (85.25 ind. × m–2). The mild velocity (type III) was most important for providing maximum density and richness. The total density (ind. × m–2) between every two current velocity types was not found significantly different except current velocity type V-I. Total 34 taxa were observed among all the stations, maximum number (22) taxa were found in type III, while lowest number (8) in type IV. However, out of 34 taxa, Glossoscolecidae was most abundant in type I velocity, Simulidae in type II, Leptoceridae in type III and V, while Psephenidae in type IV. Similarly, PCA also suggested the characteristics taxa at each velocity type.