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Aim. Analysis of the distribution and status of ctenophores Вeroe ovata and Mnemiopsis leidyi, and assessment of the parameters of their interaction in the Middle Caspian Sea.Material and Methods. The material was obtained in the western and eastern parts of the Middle Caspian Sea in September–October 2022. Large ctenophores were collected using a big cone plankton net with a 0.5 m2 opening and a 500 μm, mesh size. The number and size of large ctenophores were determined immediately after collection, larvae and eggs were counted in samples fixed with formalin to a final concentration of 4%. Zooplankton samples were collected by the Juday plankton net (0.1 m2 opening, 180 μm mesh size).Results. In September‐October 2022, a developed population of Вeroe ovata with active reproduction was recorded in the waters of the Middle Caspian Sea. The habitat area of B. ovata has significantly expanded to the north compared to 2021. Complete suppression of the Mnemiopsis population by the Beroe was observed on most of the western and eastern shelf, as well. The total number of Beroe reached 48 ind/m2, biomass – 12 g/m2. Single large individuals were found in the north of the Middle Caspian Sea at salinity 5.7 psu. The structure of mesozooplankton was still dominated by the small copepod Acartia tonsa.Conclusion. New data indicate the active development of the Вeroe ovata in the Caspian Sea, which presents a fundamental challenge for the restoration of the Caspian ecosystem. The progressive adaptation of Beroe to the conditions of the Caspian Sea has led to its expansion to the north of the Middle Caspian Sea in areas with low salinity. A complete suppression of the M. Leidyi population by the new alien noted on most of the shelf indicates an increase in its pressure on the Mnemiopsis population compared to the corresponding period of 2021.

Aim. Analysis of the first data regarding the arrival of the predatory ctenophore Beroe cf. ovata in the Caspian Sea and assessment of possible effects of its introduction for the Caspian ecosystem.Material and Methods. The material was obtained in the deep-water region of the western shelf of the middle Caspian Sea in the first ten days of October 2020. Zooplankton samples were collected using a Juday plankton net (0.1 m2 opening, 180 μm mesh size). Large ctenophores were collected using a big cone plankton net (CB) with a 0.5 m2 opening, 500 μm mesh size. Samples were taken at five stations in the 0-40 m layer. Combs larger than 5 mm were counted and measured on board the ship. The number and size of small ctenophores, larvae and eggs were determined in zooplankton samples fixed with formalin to a final concentration of 4%.Results. The presence of a new alien Beroe cf. ovata was recorded in the Dagestan shelf waters of the Caspian Sea in the beginning of October 2020. The average number of Beroe cf. ovata for five stations was 22 ind/m2 and the biomass was 6.15 g/m2. Larvae and small individuals from 5 to 20 mm in size predominated. Mnemiopsis leidyi was absent in the area investigated. The structure of mesozooplankton was dominated by the small copepod Acartia tonsa, which accounted for 92% of the zooplankton community and 78% of its biomass.Conclusion. The size structure of the B. ovata population with a predominance of larvae and small individuals indicates a recently completed breeding cycle and adaptation of the ctenophore to the conditions of the Caspian Sea. The first impacts of the new invasive ctenophore on the population of M. leidyi were demonstrated. This event may be the beginning of a new stage in the evolution of the Caspian Sea ecosystem and the restoration of its bio resources affected by the invasion of Mnemiopsis leidyi. The structure of mesozooplankton with total dominance, in abundance and biomass, of the small copepod Acartia tonsa did not differ from that in the previous period, indicating that the Caspian zoocenosis did not respond to the short-term reduction of the impact of M. leidyi. A brief analysis of the history of the introduction of ctenophores to the Black and Caspian Seas is presented and their impact on ecosystems and biological resources of these seas is studied. Based on longterm observations of the invasive ctenophores' interactions in the Black Sea, the possible outcomes of the penetration of Beroe cf. ovata in the Caspian Sea are discussed.

Aim. Analysis of new data on populations of invasive ctenopfores Вeroe ovata and Mnemiopsis leidyi in the Caspian Sea and assessment of adaptation of B. ovata to new habitat conditions.Material and methods. The data was obtained in the Dagestan sector of the Middle Caspian Sea in September‐November 2021. Ctenophores and zooplankton were collected by a big cone plankton net (BC) with a 0.5 m2 opening and a Juday plankton net (0.1 m2 opening). Small ctenophores, eggs and zooplankton content were determined in samples fixed with formaldehyde to a final concentration of 4%.Results. In September‐October 2021, the Вeroe ovata were detected in the shelf waters of Dagestan. The total number of ctenophores reached 32 ind/m2, biomass – 10 g/m2. Individuals up to 35 mm in size were recorded. The abundance of M. leidyi in areas where B. ovata was found 3‐10 times less often than in areas where it was absent. The habitat of Вeroe ovata was limited to the southern part of the Dagestan shelf and a salinity range of 7.1‐5.5 psu.Conclusion. In 2021, new data was obtained on the Вeroe ovata in the Caspian Sea. The detection of B. ovata in the Caspian Sea in 2021 indicates that the ctenophore overcame winter conditions of the Caspian Sea. The fact determines the further evolution of the Caspian Sea ecosystem. The parameters of the impact of the new alien on the population of M. leidyi were recorded. An analysis of B. ovata distribution in the waters of the Dagestan shelf depending on environmental conditions was carried out.