Abundance and size composition of ctenophore Mnemiopsis leidyi population in the Caspian Sea on 2001-06-24 to 2001-07-01

Abundance and size distribution of ctenophore Mnemiopsis leidyi in different parts of the Caspian Sea were studied in summer 2001 in relation to environmental conditions. In general, principal differences were found in M. leidyi abundance and population reproduction activity in northern-, middle- and southern Caspian waters. Ctenophore was practically absent in the northern Caspian. In the west of the middle Caspian Sea it penetrated far to the north demonstrating low reproduction activity. In the east the first single comb jellies were pointed out only in the most south of the region. In the warmest and most productive southern part of the Caspian Sea several zones of M. leidyi active breeding were found with total abundance exceeding 6000 #/m**2. Breeding activity and abundance of ctenophores increased here from the east to the west exceeding maximum values along the western coast of the southern Caspian Sea in regions of intensive sprat catching. Dependence of M. leidyi population development on temperature conditions was mentioned. On the base of remote sensed surface temperature, chlorophyll, and suspended mater distribution analysis possible ctenophore settling mechanisms by mesoscale dynamic structures were examined. Practical applications of obtained results are discussed for using effective biological methods to prevent catastrophic consequences of M. leidyi invasion to the Caspian Sea

Current State and Economic Value of Astacofauna in Certain Areas of the Eastern Shelf of the Caspian Sea

Aim. The purpose of this work was to assess the current state of crayfish populations in their habitats on the eastern shelf of the Caspian Sea (Alexander Bekovich‐Cherkassky Bay).Material and Methods. Fieldwork was based on underwater research methods using light diving equipment. Collection of research material was carried out according to an established crayfish survey protocol using fixed grid sites of 100 square metres. Collected crayfish were identified by species, measured and weighed, fecundity of females and the condition of crayfish shells were recorded. Crayfish were then released back into the sea. Calculation of numbers was carried out on the basis of determination of cluster density (ind/m2) with a further assessment of useful biotype areas. Calculation of commercial stocks based on crayfish length. The research synthesized information derived from comparative analysis of modern research results and archival data from the 1970s to 1990s.Results. Analysis showed that significant changes in the composition of populations had occurred. The dominant species recorded was Caspiastacus pachypus Rathke which has substantially displaced from the biotopes Pontastacus eichwald  Воtt. which was previously the dominant species here.Conclusion. Comparative analysis of the modern state of the astacofauna on the eastern shelf and historical data indicates significant changes in the structure of populations of Caspian crayfish. The resilient C. pachypus has become the dominant species. Its small commercial size has significantly reduced the economic value of crayfish stocks. In general, however, commercial stocks of these crayfish make it possible to develop these marine biological resources

DEVELOPMENT OF LOCAL COMMUNITIES ON THE BASIS OF EXPERIMENTAL BOTTOM STATIONS IN DIFFERENT ZONES OF THE NORTH-CASPIAN SHELF

Aim. On the basis of four experimental bottom stations installed at various depths of the North Caspian shelf, the local communities of marine organisms were formed, on various constructions and in close proximity to them were investigated. The aim of the work is to study the features of community development on the basis of bottom biological stations, to measure their quantitative characteristics, to assess the informative character of the structural and functional characteristics of local communities for analyzing the state of the marine environment. Methods. Experimental bottom stations were installed in various regions of the North Caspian shelf using diving equipment to study their impact on the environment. Control over the development of associated fauna was carried out with the help of traps and the method of direct accounting for the materials of photo-video surveys. Sampling of fouling was carried out by the method of registration sites. Based on the number of species of flora and fauna of local communities, a ballroom information system has been suggested, that can be used for monitoring. Results. Research materials indicate a significant difference in the species composition, biomass and the structure of communities of local cenoses formed at the bottom stations with the same design and ecological capacity at various depths of the North Caspian shelf. In the shallow shelf zone at depths of 6-8 m in the local community of the bottom station, the vegetation component is dominant. At great depths, the total biomass increases in local cenoses and animal communities, including filter-feeders, make significant contribution to the self-purification of the marine environment. Conclusions. The results indicate the possibility of using complex observations of the structure and functional characteristics of local communities formed on the base of bottom stations, as well as the development of species of indicators and objects of accumulation of toxicants for assessing the state of the marine environment. The development of this approach involves the experiments with different station costructioons and materials and use of biotechnology implantation of test organisms on the design of bottom stations