ОТНОШЕНИЕ КОЛЬЧАТЫХ И КРУГЛЫХ ЧЕРВЕЙ К КИСЛОРОДУ В ЗАПАДНОЙ ЧАСТИ СЕВЕРНОГО КАСПИЯ

Abstract

Oxygen deficiency is caused by temperature and salinity stratification of water masses. Hypoxia was formed mainly on the border of the Northern Caspian - Middle Caspian, in shallow areas (up to 5 m depth), as well as in areas with fine-grained sediments. Representatives of annelid (Annelida) and round (Nemathelminthes) worms are characterized by high frequency. During the study period (2013-2017) the abundance and biomass of the study group varied widely. Oligochaeta was dominated by the total number, Hirudinea - by the total biomass. The maximum frequency was characteristic for polychaetes Hediste diversicolor . The dynamics of quantitative indicators of worms was inversely dependent on changes in the area of hypoxia: the expansion of the hypoxic area showed the decreased number of worms. The limits of tolerance to the oxygen content in individual species and classes of worms living in the north part of the Caspian Sea have been studied. The minimum concentration of oxygen recorded for the entire study period (1.29 ml/l; 21%) is found not critical for Hediste diversicolor and Hypaniola kowalewskii . The low concentration (1.76 ml/l; 31%) does not inhibit the development of Oligochaetas. The other representatives of Vermes group living in the western part of the Northern Caspian were found under the absolute oxygen content exceeding 4.06 ml/l and under the relative oxygen content exceeding 44%. A wide ecological valence for oxygen is characteristic for Hediste diversicolor , Hypaniola kowalewskii and Oligochaeta . Fabricia sabella , Caspiobdella tuberculosis and Archaeobdella esmonti demonstrate the narrow range of oxygen tolerance.