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The purpose of this work is to analyse the influence of external factors on quantitative variables of Eurytemora affinis in water bodies of Kazakhstan. In 1997-2018, more than 150 water bodies located in various regions of the country were surveyed. The results obtained and analysis of the published literature showed that E. affinis primarily inhabits small shallow water bodies of Central and Eastern Kazakhstan. Populations from the North-Eastern Caspian Sea, originally identified as “Eurytemora affinis”, could be attributed to the recently described species Eurytemora caspica. In the water bodies examined, E. affinis was found at water temperatures from 12 to 25°C and at salinities from 0.2 to 7.1 g/dm3. The highest abundance of Eurytemora was recorded at 21-22°C and a salinity of 1.0-3.0 g/dm3. The optimum temperature range in the water bodies examined in an extreme continental climate is higher than the values given for E. affinis in water bodies in a moderately temperate climate. The optimal TDS [Total Dissolved Solids] value (1.0-3.0 g/dm3) has shifted towards more truly fresh waters than was stated for E. affinis collected from the sea (6.2-8.2), and this was confirmed in experiments (from 3.0-10.0 to 10.0-15.0). In the majority of the examined water bodies of Kazakhstan, males dominated the Eurytemora populations. Male dominance in E. affinis populations might be due to the adverse effect of elevated temperature on the lifespan of females, and it was also connected with the level of toxic pollution of the water bodies. It seems that E. affinis endures a relatively high content of heavy metals, but it does not inhabit water bodies with very high toxic pollution. The revealed features of E. affinis’ biology in Kazakhstan water bodies might be associated with both the heterogeneity of its populations from different parts of the range, and the existence of a complex of closely related species that at present is collectively named “Eurytemora affinis”. |
