Investigation on Identification, Density and Distribution of Zooplankton in Lar Reservoir in Iran

Abstract

For optimum management, some limnological variables and zooplankton identification, density and distribution in Lar reservoir were studied over a two-year cycle (2008 and 2009) during the ice-free seasons (May to October). Samples were taken by simple plankton net (55im mesh size) from various depth layers (10-0 m, 10-20 m, 20-30 m) and were fixed with formalin 4% In the laboratory they were studied with inverted microscope. In this survey, we identified 21 genera in 3 zooplanktonic orders. The order of Cladocera was predominant and comprised 55.81 % of population annually. The predominate species and genera were Bosmina coregoni, Daphnia pulex, Daphnia longspina and embryonic Cladocerus. The order of Rotatori a comprised the second position with species of Asplanchna brightwelli, Polyarthera dolicopthera, Syncheata pectinata and Keratella cochlearis (percentage composition 37.71). Copepoda constitute 6.45 percentage compositions with five species and genera Cyclops vulgaris, C. smirnovi, Eucyclops sp., Arctodiaptomus acutilobatus and Copepoda Naupli. The mean density of for the sampling all monthly, mean of dominant Zooplanktonic density belonged to Cladocera order (32968.83±123.40 number/m ) while they were 3 Non-parametric statistical analysis based on Kruskal-Walli s and Mann-Whitney showed that there were significant differences between zooplankton abundance in different stations and months (P 0.05). Biological studies indicated that this reservoir has low potential to planktonic productivity and due to geographical location of this dam, remarkable temperature differences can be observed in different years especially in fall and winter, which is biologically important.