In this study, the effects of water withdrawal on the lake Artemia population was studied during 12 months from Esfand 1400 to Bahman 1401. Six sampling sites were selected in northern and southern parts of the lake. Samplings were performed monthly. Several physicochemical factors were determined such as water temperature, pH, transparency, salinity, water level, lake surface area, lake volume, Total Dissolved Solids (TDS) and Electeric Conductivity (EC). Furthermore, Artemia life stages including cysts, nauplious, meta-nauplious, juvenile and adults densities were determined. Phytoplankton density was determined by invert microscopy method. Statistical analysis were carried out by PAST software version 3.04. The results showed that reduced water level imposed complete Artemia biomass elimination and sever cysts density drop. Seven algal species were identified. Dunaliella spp. composed 98.63% of phytoplankton density alone. In general, the results of this study suggested that the surface area, volume, and level of the lake were the most influential parameters on the lake's cyst density. Electrical conductivity, salinity and TDS of water exerted a moderate effect on the amount of cyst in the lake. And finally, pH and phytoplankton density were the least influential parameters on Artemia cyst density. While in the present study, no species of Artemia in the form of biomasses (Nauplii, meta naupli, young and adult Artemia) were observed in the lake and the number of cysts reported was 0.128 ± 0.31, which showed that the number of cysts has decreased about 36 times compared to the two years ago. In the summer and autumn (dry) seasons, the number of cysts was 0.00216 ± 0.0017 and 0.000 per liter, respectively, and in the spring and winter (wet season) there was 0.364 ± 0.259 and 0.149 ± 0.084 cysts per liter, respectively. Kazem Dashi, Zanbil, Agh Gonbad and Myangozar stations accounted for the average annual cyst density with 0.0243 ± 0.063, 0.1223 ±  0.237, 0.1428 ± 0.222 and 0.2262 ± 0.546 cysts per liter, respectively.  Due to absence of any biomass of Artemia in Urmia Lake, cyst harvesting is not recommended at water levels below the 1271 m. These cysts are the result of washing by precipitation and water flows that extrude the cysts stuck between salt crystals and sediments. Indeed, any cysts have not been produced by Artemia in these circumstances, so cyst harvesting can obviously lead to irreparable damage on Artemia stocks and cyst bank of Urmia Lake.
Keywords: Artemia, Dunaliella, Cyst, Urmia lake, Water level, Salinity
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