Study of diversity and distribution of Oligochaeta fauna in Sefidroud estuary (South Caspian Sea)

Aquatic oligochaetes play a considerable role in the organic matter processing, food chains of water communities and fish feeding. In order to diversity and distribution pattern and how their relationship with environmental conditions in Sefidroud estuary (South Caspian Sea basin) was studied. Sampling of substrate sediments was carried out bimonthly from November ۲۰۱۴ to September ۲۰۱۵, using Van Veen grab (۰.۰۳ m۲). Sampling was carried out at three stations (S۱ in the river, S۲ in estuary and S۳ in the marine), with three replicates. In the present study, two families were identified, including Tubificidae (۸ species) and Lumbriculidae (۳ species). ۵ species were reported from the Sefidroud river for the first time. Among identified species, the highest and lowest average densities were related to Limnodrilus hoffmeisteri (۱۰۷۲.۱ ind. m-۲) and Euilyodrilus caspicus (۱۱.۱ ind. m-۲), respectively. Results of monthly distribution showed that the highest and lowest densities of Oligochaeta fauna were in July (۱۵۴۸.۱±۶۲۸ ind. m-۲) and in November (۲۰۸.۳±۸۸ ind. m-۲) respectively which were significantly different, by Duncan's test (p<۰.۰۵). Among sampling stations, river station (S۱) showed higher density (۴۱۴.۲±۱۸۷ ind. m-۲) than estuary station (S۲) (۰±۰ ind. m-۲) and marine station (S۳) (۳۶۲.۴±۱۳۱ ind. m-۲) which were significantly different (p<۰.۰۵).