36 March 2012 Drought in Urmia Lake, the largest natural habitat of brine shrimp Artemia Alireza Asem1,2 and Fereidun Mohebbi3, Reza Ahmadi3 Fig. 1. Clear evidence of the retreating coastline of Urmia Lake. Fig.2. The difficult and disrupted life of waterbirds. Urmia Lake is an oligotrophic and extremely hypersaline lake that is the largest natural habitat of brine shrimp Artemia (Ahmadi 2005, Eimanifar and Mohebbi 2007). It has a surface area between 4000 and 6000 km2 and a maximum depth of 16 m, located in northwestern Iran at an elevation of 1274 m. Salinity of lake water ranges between 120 and 280 g/L. Urmia Lake is the saltiest lake on earth with an active food web. It is a UNESCO biosphere reserve and a Ramsar wetland (Asem et al. 2010). Urmia Lake has been experiencing a serious ecological crisis over the past decade. Lake water is saturated with salts to the point where salt crystals form on the lake surface year round. The salinity of Urmia Lake has increased from 169 g/L in 1995 to more than 300 g/L in 2003-2004 (Fig. 1) (Sorgeloos 1997, Ahmadi 2005, 2007). Many hectares of surrounding land have been converted to salt marshes and, in the southern and southeastern areas, the coastline has retreated several kilometers (Fig. 2). The salt-saturated water of the lake has disrupted the development of waterbirds (Fig. 3). In 1995, Artemia urmiana cyst production (dry weight) in the surface half-meter of Urmia Lake was calculated by integration and summation to range from 4243 to 4536 t/ yr. The lake area was estimated to be 5500 km2 that year. The concentration of cysts can be estimated as follows: 1) lake area in 1995: 5500 km2 = 5,500,000,000 m2 2) volume in 0.5 m of lake surface = 5,500,000,000 × 0.5 = 275 × 107 m3 = 275 × 1010 L 3) 1 g of cysts = 250,000 cysts (Sorgeloos 2007) mean biomass of dry cysts in 0.5 m of lake surface (t) = (ai + as)/2 = (4243 + 4536)/2 = 4389 t/yr = 438,914 × 104 g/yr, where ai = amount of dry cysts calculated by integration as = amount of dry cysts calculated by summation 5) number of cysts in 0.5 m of lake surface = (438,914 × 104) × 250,000 = 10,972,925 × 108 cysts 6) concentration of cysts = (10,972,925 × 108) / 275 × 1010 = 399 cysts/L Since 2000, with the drought in Urmia Lake, the harvest of Artemia cysts has collapsed (Ahmadi 2005). A resource assessment of A. urmiana measured cyst concentrations in the surface 20 cm of 27 cysts/L (2003) and 25 cysts/L (2004) (Ahmadi 2005). Cyst concentrations declined further to 11 (2005), 8 (2006), and 3 (2007) cysts/L (Ahmadi Fig 3. Annual salinity of Urmia Lake in different years
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