Экологическая валентность к кислороду северокаспийских мизид и кумовых ракообразных

Abstract

The paper focuses on the problems of violation of the ecological balance, changes in the nutrient load, undermining the ecosystem’s biopotential, caused by anthropological pressure and resulting in deterioration of the oxygen regime in the bottom layer of water. The purpose of the research was to determine the environmental oxygen tolerance in bottom invertebrates, representatives of the orders Mysidacea and Cumacea, which are forage objects for beluga, sturgeon, stellate sturgeon, bream and pike perch. The research was conducted in 2013-2017 in the western part of the North Caspian. Developing of oxygen deficiency in the studied water area was due to thermohaline stratification of water masses. Hypoxia was formed in local areas. Representatives of Mysidacea predominantly inhabiting the bottom layers have a low frequency of occurrence, because they live in a narrow range of oxygen content (about 5-7 mg/l). A low oxygen concentration (less than 3.95 ml/l (74%)) inhibits the development of Mysidacea. Paramysis ullskyi prevailed in the total number of samples taken from macrozoobenthos, and Paramysis lacustris prevailed in the total biomass. Limnomysis benedeni and Paramysis ullskyi were the most resistant to oxygen deficiency. These species have a maximum ecological valence to oxygen. Representatives of the order Cumacea are characterized by a high frequency of occurrence. The species Schizorhynchus bilamellatus dominated in the surveyed water area, both in abundance and biomass. Cumacea live in a wide variability of oxygen content. Schizorhynchus bilamellatus and Stenocuma graciloides are most resistant to oxygen deficiency. These species have a maximum ecological valence to oxygen. The minimum oxygen recorded over the entire research period (1.29 ml/l; 21%) is not critical for Stenocuma graciloides. The results of the study are of practical value for assessing the condition of the food supply of benthos-eating fish that are commercialized in the western part of the North Caspian