Ecological investigation of zooplankton abundance in the river Haraz, northeast Iran: Impact of environmental variables

The influence of physicochemical properties of Haraz river on its zooplankton composition and abundance were investigated at three sites for one year between August 2009 and July 2010. The present study records for the first time the aspects of zooplankton diversity and composition in relation to the physicochemical environment of the Haraz river. Only three groups of zooplankton were found: Rotifera with eighteen genera; Cladocera with nine and Copepoda with six genera. Rotifera was the predominant group (64.89%), followed by Cladocera (19.62%) and Copepoda (15.32%). Upstream, the abundance was 805 individuals/m3, while it varied from 922 to 1126 ind/m3 downstream. Alkaline pH and nutrients were the main environmental factors which affected zooplankton abundance in the river. Site variation in dominance, diversity, evenness and richness were calculated. The study revealed that the presence of certain species, such as Lepadella sp., Mesocyclops sp., Polyarthra sp. and Brachionus sp. is considered to be a biological indicator for eutrophication. The calculated Jack1 values of sites 1 to 3 were 7.624, 16.426 and 19.221, respectively. The Shannon-Wiever species diversity index (H’) values were also different for all the three sites viz., site 1 (1.992), site 2 (1.21) and site 3 (2.48). Simpson’s dominance index (H) value was highest at site 1 (0.692), indicating maximum dominance, whereas at site 3 dominance was the lowest (0.227) and diversity was the highest. Overall, our results showed that changes in the water quality of the river Haraz have considerable effects on the composition of zooplankton assemblages that can potentially affect the functioning of these ecosystems.