Substratum as Determining Factor for the Distribution of Benthic Macroinvertebrate Fauna in a River Ecosystem

Present study was focused on the Ken river for determination of the distribution of benthic macroinvertebrate fauna with respect to substrate variation. The invertebrate samples were collected during December 2003 to March 2004 at four different stations by lifting of stones and sieving of clay–silt substratum from 0.09 m2 area. The collected samples were preserved in 5 % formalin and identified at family level. The count data was used to determine the density and composition of benthic macroinvertebrate fauna. Total mean density decreased from station S1 to S3 but increased at S4 and differed significantly among the stations. The maximum density was found in the stony substratum (boulder and cobble) as compared to small particle size (pebble, gravel and sand). The fauna was predominated by insects at stations S1 (84 %), S2 (90 %) and S3 (93 %), while reduced at S4 (48 %). Neoephemeridae and Caenidae were abundant taxa in boulder–cobble and cobble–pebble substrate, respectively. Leptophlebiidae, Baetidae and Hydropsychidae were abundant at pebble–gravel substrate and Thiaridae–Chironomidae–Nephthydae were abundant in silt–clay substrate. Principal component analysis also indicated the above observation. Canonical correspondence analysis at each station indicated that substratum (abiotic and biotic) was responsible for the distribution of benthic macroinvertebrate fauna in the Ken. Functionally, the collector insects dominate the fauna, at all the four stations because of substratum as well as the continuous source of particulate organic matter in the river.