Biodiversity of Planktonic Rotifers along a horizontal salinity gradient in the Bahmanshir River estuary (Northern Persian Gulf)

The present study aimed at evaluating the biodiversity of planktonic rotifers in a horizontal salinity gradient in both summer and winter 2014 at the Bahmanshir river estuary. Planktonic rotifers were sampled using 100 μm mesh size plankton net from six stations with three replications. In this study, 14 species of rotifers belong to 6 genera and 3 families were identified. The species Brachionus rotundiformis and B. plicatilis were dominant at all stations. Environmental factors such as temperature, salinity and dissolved oxygen were also measured. The results of Spearman correlation test showed that the highest negative relationship between electrical conductivity and salinity with -0.94 and -0.93 correlation coefficient respectively with abundance of rotifers (P<0/05). So along the salinity gradient toward the stuary mouth species structure was changed and speceies richness decreased. Results indicate that differences in salinity between stations of the river account for differences in the species composition and diversity. The highest abundance of rotifers was found in summer and in station 1 (1362.1 per cubic meter) and In the winter there were no rotifers observed in station 6. Maximum amounts of Shannon- Weaner index of diversity in summer and dominance index of Simpson were estimated in summer and winter with amount of 1.52 and 0.4 respectively. The results of this study showed that salinity is the most influential factor on the diversity and density of rotifers in the Bahmanshir river.