Abstract
The article highlights the processes of lowering and raising the Caspian Sea level and its influence on the quantitative and qualitative characteristics of the aquatic bioresources, including zoobenthos. The development of macrozoobenthos in the Caspian Sea including the Northern Caspian is associated with various processes: chemical, physical and biological. The presence of macrozoobenthos determines the fish productivity in the sea, it is an integral part of the ecosystem of the northern part of the Caspian Sea. In this regard, the assessment of the composition and quantitative characteristics of bottom communities becomes important. One of the urgent tasks of modern hydrobiology is detecting the basic regularities in the biotic processes that affect the qualitative and quantitative changes in the aquatic organisms. This research is of a retrospective nature. On the basis of a long-term analysis of the dynamics of the species structure of bottom zoocenoses there have been revealed the changes in the macrozoobenthos of the western part of the Northern Caspian in the first and second periods of the sea level rise (1978–1988 and 1989–1995). Decreasing water salinity, increasing desalinated zones and areas with oxygen deficiency in the bottom horizon (in the extremely high-water years of 1990 and 1991) contributed to the significant changes in the quantitative and qualitative composition of the bottom fauna. From the first stage to the second there was recorded a decrease in the number and biomass of crustaceans and molluscs. The species Stenogammarus macrurus (G. O. Sars) and Stenogammarus similis (G. O. Sars), which are tolerant to the significant salinity fluctuations, as well as abra, which is resistant to oxygen deficiency were most abundant in the water complex with light salinity. Also, there has been considered the water content of the rivers of the Caspian basin and the type of soil as factors influencing changes in the concentration of macrozoobenthos.
Highlights
The development of macrozoobenthos in the Caspian Sea including the Northern Caspian is associated with various processes: chemical, physical and biological
The presence of macrozoobenthos determines the fish productivity in the sea, it is an integral part of the ecosystem of the northern part of the Caspian Sea
On the basis of a long-term analysis of the dynamics of the species structure of bottom zoocenoses there have been revealed the changes in the macrozoobenthos of the western part of the Northern Caspian in the first and second periods of the sea level rise (1978–1988 and 1989–1995)
Summary
Волжско-Каспийский филиал Всероссийского научно-исследовательского института рыбного хозяйства и океанографии, Астрахань, Российская Федерация. А следовательно, и понижения уровня моря половина западной части Северного Каспия оказалась занята водами с повышенной соленостью – 12 ‰, что выше на 3,4 ‰ показателей 1934 г. Повлекшим снижение солености Северного Каспия, наблюдалось восстановление развития донных беспозвоночных, что отразилось на показателях их численности и биомассы. На этапе I (подъем уровня Каспийского моря равномерный) изменение гидролого-гидрохимического режима значительно повлияло на количественное развитие донной фауны западной части Северного Каспия. Corophiidae (в 2 и 3 раза соответственно), что обусловлено значительным распреснением западной части Северного Каспия на II этапе – этапе резкого поднятия уровня моря. Амфиподы в западной части Северного Каспия были представлены всеми экологическими группами, однако в оба периода исследований превалирующими являлись виды слабосолоноватоводного комплекса (30 видов). Сокращение количественных величин ракообразных и моллюсков в западной части Северного Каспия в период 1989–1995 гг.
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