The ctenophore Beroe cf. ovata in the Caspian Sea. The beginning of a new stage in the evolution of the Caspian ecosystem?

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.

1. Vinogradov M.E., Vostokov S.V., Arashkevich E.G., Drits A.V., Musaeva E.I., Anokhina L.L., Shushkina E.A. [The Peculiarties of the Comb-Bearers Introducers Biology and their Role in the Black Sea Ecsystem]. In: Vidy-vselentsy v evropeiskikh moryakh Rossii [Species Introducers in the European seas in Russia]. Apatity, 2000, pp. 91-113. (In Russain)

2. Consulov A. It's another single prisylat. Morski Svyat. 1989. N 2. 25 p.

3. Vinogradov M.E., Shushkina E.A., Musaeva E.I., Sorokin P.Yu. New invader in the Black Sea-the Cte-nophora Mnemiopsis leidyi (A. Agassiz) (Ctenophora: Lobata). Okeanologiya [Oceanology]. 1989. vol. 29, no. 2, pp. 293-299. (In Russian)

4. Shushkina E. A., Musaeva E. I. Structure of the plankton community of the Black Sea epipelagial and its changes in connection with the introduction of a new species of ctenophore. Okeanologiya [Oceanology]. 1990, vol. 30, no. 2, pp. 324-328. (In Russian)

5. Zaika V.E., Sergeeva N.G. Morphology and development of the universal Ctenophora Mnemiopsis mccradyi (Ctenophora: Lobata) in the Black Sea. Zoo-logicheskii zhurnal [Zoological journal]. 1990, vol. 69, no. 2, pp. 5-10. (In Russian)

6. Shushkina E.A., Nikolaeva G.G., Lukasheva T.A. Changes in the structure of the plankton community of the Black Sea during the mass development of the ctenophore Mnemiopsis leidyi (A. Agassiz). Zhurnal obshchei biologii [Journal of General biology]. 1990, vol. 51, no. 1, pp. 54-60. (In Russian)

7. Shushkina E.A., Vinogradov M.E. Long-Term variability of plankton in open areas of the Black Sea. Okeanologiya [Oceanology]. 1991, vol. 31, no. 6, pp. 973-980. (In Russian)

8. Vinogradov M.E., Shushkina E.A., Nikolaeva G.G. [Mass development of Mnemiopsis comb as a manifestation of anthropogenic impact on the marine ecosystem. Black Sea]. In: Prakticheskaya ekologiya morskikh regionov. Chernoe more [Practical ecology of marine regions]. Kiev, Naukova Dumka Publ., 1990, pp. 94-102. (In Russian)

9. Vinogradov M.E., Sapozhnikov V.V., Shushkina E.A. Ekosistema Chernogo morya [Ecosystem of the Black Sea]. Moscow, Nauka Publ., 1992, 112 p. (In Russian)

10. Volovik S.P., Luts G.N., Mirzoyan E.A., Pryakhin Yu.V., Rogov S.F., Studenikina E.I., Revin N.I. Introduction of Mnemiopsis combs into the sea of Azov: preliminary assessment of consequences. Rybnoe khozyaistvo [Fisheries]. 1991, no. 1, pp. 47-49. (In Russian)

11. Volovik S.P., Myrzoyan Z.A., Volovik G.S. Mnemi-opsis leidyi in the Azov Sea: biology, population dynamics, impact to the ecosystem and fisheries. ICES Statutory Meeting. Sept., 1993, C.M. 1993 (L:69). ICES: Copenhagen. p. 30.

12. Tsikhon-Lukanina E.A., Reznichenko O.G. Nutrition Features of different-sized individuals of the Mnemi-opsis comb in the Black Sea. Okeanologiya [Oceanology]. 1991, vol. 31, no. 3, pp. 442-446. (In Russian)

13. Tsikhon-Lukanina E. A., Reznichenko O. G., Lukasheva T. A. Quantitative patterns of nutrition of the Black Sea ctenophore Mnemiopsis leidyi. Okeanologiya [Oceanology]. 1991, vol. 31, no. 2, pp. 272-276. (In Russian)

14. Tsikhon-Lukanina E.A., Reznichenko O.G., Lukasheva T.A. Eating of fish larvae by the combworm Mnemiopsis leidyi in the coastal waters of the Black Sea. Okeanologiya [Oceanology]. 1993, vol. 33, no. 6, pp. 895-899. (In Russian)

15. Tsikhon-Lukanina E.A., Reznichenko O.G., Lukasheva T.A. Ecological variability of the population of the Ctenophora Mnemiopsis leidyi (Ctenophora) in the Black Sea. Zhurnal obshchei biologii [Journal of General biology]. 1993, vol. 54, no. 6, pp. 713-721. (In Russian)

16. Tsikhon-Lukanina E.A., Reznichenko O.G., Lukasheva T.A. Food Diversity in the Ctenophora Mnemiopsis leidyi (Ctenophora Lobata) in the Black Sea coast. Zoologicheskii zhurnal [Zoological journal]. 1999, vol. 78, no. 8, pp. 916-921. (In Russian)

17. Sergeeva N.G., Stutterer V.E., Mikhailova T.V. Nutrition of Mnemiopsis mccradyi in the Black Sea. Ekologiya morya [Marine ecology]. 1990, iss. 35, pp. 18-22. (In Russian)

18. Pavlova E.V., Minkina N.I. Breath of the Black Sea Ctenophora (Ctenophora, Lobata, Mnemiopsis). Dokla-dy Akademii Nauk [Reports of the Academy of Sciences]. 1993, vol. 333, no. 5, pp. 682-683. (In Russian)

19. Finenko G.A., Abalmasova G.I., Romanova Z.A. Nutrition, oxygen consumption, and growth of Mnemi-opsis mccrady depending on food concentration. Bi-ologiya morya [Marine Biology]. 1995, vol. 21, no. 5, pp. 315-320. (In Russian)

20. Shushkina E.A., Vinogradov M.E., Lukasheva T.A., Lebedeva L.P., Vostokov S.V. Comparative use of various plankton fishing tools for monitoring long-term changes in the black sea communities. Okeanologiya [Oceanology]. 2003, vol. 43, no. 5, pp. 744-750. (In Russian)

21. Vinogradov M.E., Shushkina E.A., Mikaelyan A.S., Nezlin N.P. Temporal (seasonal and interannual) changes of ecosystem of the open water of the Black Sea. In: Environmental degradation of the Black Sea: challenges and remedies. (ed. S. Besiktepe et al). Netherlands. Kluwer Academic Publishers, 1999, vol. 56, pp. 109-129. DOI: 10.1007/978-94-011-4568-8_8

22. Vinogradov M.E., Shushkina E.A., Bulgakova Yu.V., Serobaba I.I. Zooplankton Eating by comb Mnemiopsis and pelagic fish in the Black sea. Okeanologiya [Oceanology]. 1995, vol. 35, no. 4, pp. 569-573. (In Russian)

23. Kideys A.E. Recent dramatic changes in the Black Sea ecosystem: the reason for the sharp decline in Turkish anchovy fisheries. Journal of Marine Systems, 1994, vol. 5, iss. 2, pp. 171-181. DOI: 10.1016/0924-7963(94)90030-2

24. Opportunistic settlers and the problem of the cten-ophore Mnemiopsis leidyi invasion in the Black Sea. GESAMP Reports and Studies, no. 58. IMO, UNEP, London, 1997, 84 p.

25. Chikina M.V., Kucheruk N.V. Long-term changes in the structure of coastal benthic communities in the Northeastern part of the Black Sea: influence of alien species. Oceanology. 2005, vol. 45, suppl. 1, pp. S176-S182.

26. Kucheruk N.V., Flint M.V., Maksimova O.V., Chikina M.V., Simakova U.V. [Modern dynamics of benthic communities of the North-Eastern shelf of the Black sea]. In: Izmenenie prirodnoi sredy Rossii v XX veke [Changes in the natural environment of Russia in the twentieth century]. Moscow, Molnet Publ., 2012, pp. 247-288. (In Russian)

27. Ivanov V.P., Kamakin A.M., Ushivtzev V.B., Shigano-va T.A., Zhukova O., Aladin N., Susan I., Wilson S.I., Harbison G.R., Dumont H.J. Simultaneous invasion of the Caspian Sea by two jellies Mnemiopsis and Aurelia. Journal Biological Invasions. 2000, no. 2, pp. 255-258.

28. Vostokov S.V., Ushivtsev V.B., Lisitsyn B.E., Solovyov D.M. Summer state of the population of Mnemiopsis leidyi - an invader in the Caspian Sea and its relation to habitat conditions. Okeanologiya [Oceanology]. 2004, vol. 44, no. 1, pp. 90-98. (In Russian)

29. Kamakin A.M., Egorov S.N. Vliyanie populyatsii Mnemiopsis leidyi na razlichnye troficheskie urovni ekosistemy Kaspiiskogo morya [Influence of Mnemi-opsis leidyi population on various trophic levels of the Caspian Sea ecosystem]. Trudy I Mezhdunarodnogo foruma (6-i Mezhdunarodnoi konferentsii) «Aktual'nye problemy sovremennoi nauki. Estestvennye nauki», Samara, 2005 [Proceedings of the I International Forum (6th International Conference) “Actual problems of modern science. Natural science”, Samara, 2005]. Samara, 2005, part 13, Ecology, pp. 65-72. (In Russian)

30. Kamakin A.M., Chizenkova O.A., Zaizev V.F. Mnemi-opsis leidyi impact on some trophical chains of the Caspian Sea. Yug Rossii: ekologiya, razvitie [South of Russia: ecology, development]. 2010, vol. 5, no. 2, pp. 6774. (In Russian)

31. Kamakin A.M., Zaitsev V.F. Regularities of long-term and interseasonal dynamics of the ctenophore Mnemi-opsis leidyi population in the Caspian Sea. Yug Rossii: ekologiya, razvitie [South of Russia: ecology, development]. 2012, vol. 7, no. 1, pp. 96-102. (In Russian)

32. Zaitsev V.F., Kamakin A.M., Volkova I.V., Yurchenko V.V., Matveeva N.I., Biryukova M.G. [Nutrition of the ctenophila Mnemiopsis leidyi in the Caspian sea]. In: Ekologicheskie aspekty prirodopol'zovaniya Severnogo Prikaspiya [Ecological aspects of nature management in the Northern Caspian region]. 2017, pp. 299-348. (In Russian)

33. Kamakin A.M., Khodorevskaya R.P. Impact of the alien species Mnemiopsis leidyi A. Agassiz, 1865 on fish of the Caspian Sea. Inland Water Biology, 2018, no. 2, pp. 51-56. (In Russian) DOI: 10.7868/S0320965218020067

34. Kamakin A.M., Khodorevskaya R.P., Paritckij Yu.A. Influence of invader ctenophoran Mnemiopsis leidyi (А. Agassis, 1865) on the general parts of the Caspian Sea ecosystem. Vestnik of Astrakhan State Technical University. Series: Fishing industry, 2018, no. 1, pp. 1-14 (In Russian) DOI: 10.24143/2073-5529-2018-1-35-48

35. Kamshilov M.M. The feeding of ctenophore Beroe cucumis Fab. Doklady AN SSSR [Reports of the USSR Academy of Sciences]. 1960, vol. 130, no. 5, pp. 11381140. (In Russian)

36. Swanberg N.R. The feeding behavior of Beroe ovate. Marine Biology, 1974, vol. 24, pp. 69-76. DOI: 10.1007/BF00402849

37. Tamm S.L., Tamm S. Reversible epithelial adhesion closes the mouth of Beroe, a carnivorous marine jelly. Biol Bull., 1991, vol. 181, iss. 3, pp. 463-473. DOI: 10.2307/1542367

38. Konsulov A., Kamburska L., Moncheva S., Krastev A., Prodonov K. The invasion of Beroe ovata in the Black Sea. Why a warning for ecosystem concern? Oceanography of the Eastern Mediterranean and Black Sea. Athens. Abstracts. 1999, pp. 79-80.

39. Vinogradov M.E., Shushkina E.A., Anokhina L.L., Vostokov S.V., Kucheruk N.V., Lukasheva T.A. Mass development of the Beroe ovata eschocholtz comb-leaf near the North-Eastern coast of the Black Sea. Okeanologiya [Oceanology]. 2000, vol. 40, no. 1, pp. 52-55. (In Russian)

40. Vostokov S.V., Arashkevich E.G., Drits A.V,. Lukashev Yu.F. Ecological and physiological characteristics of the Beroe ovata comb in the coastal zone of the Black Sea: population, biomass, size characteristics of the population, behavior, nutrition, metabolism. Okeanologiya [Oceanology]. 2001, vol. 41, no. 1, pp. 109-115. (In Russian)

41. Arashkevich E.G., Anokhina L.L., Vostokov S.V., Luppova N.E. Reproductive strategy of the ctenophore Beroe ovata (Ctenophora. Tentaculata. Beroid) - a new invader in the Black Sea. Okeanologiya [Oceanology]. 2001, vol. 41, no. 2, pp. 116-120. (In Russian)

42. Luppova N.E. Black Sea invasive comb jelly Beroe ovata (ctenophore, atentaculata, beroida): reproductive success depending on habitat conditions. Byulleten' nauki i praktiki [Bulletin of Science and Practice]. 2018, vol. 4, no. 10, pp. 31-46. (In Russian)

43. Finenko G.A. Romanova Z.A. Abolmasova G. I. New invader in the Black sea ctenophore Beroe Ovata Brunguiere. Ekologiya morya [Marine ecology]. 2000, iss. 50, pp. 21-25. (In Russian)

44. Vinogradov M.E., Shushkina E.A., Vostokov S.V., Vereshchaka A.L., Lukasheva T.A. Interaction between the populations of the ctenophores Mnemiopsis leidyi and Beroe ovata off the Caucasian Coast of the Black Sea. Oceanology. 2002, vol. 42, no. 5, pp. 693-701.

45. Shiganova T.A., Legendre L., Kazmin A.S., Nival P. Interactions between invasive ctenophores in the Black Sea: assessment of control mechanisms based on longterm observations. Marine ecology progress series, 2014, vol. 507, pp. 111-123. DOI: 10.3354/meps10806

46. Luppova N.E., Arashkevich E.G. [Current state of the Black Sea macrozooplankton in the shelf zone of the sea]. In: Nazemnye i morskie ekosistemy Pricher-nomor'ya i ikh okhrana [Terrestrial and marine ecosystems of the black sea region and their protection]. 2018, pp. 90-91. (In Russian)

47. Volovik S.P., Korpakova I.G. Materials for the biological justification of the introduction of Beroe Ovata into the Caspian Sea as a factor of biocontrol over the development of the Mnemiopsis population. Nauchnyi byulleten' Kaspiiskogo plavuchego universiteta [Scientific Bulletin of the Caspian Floating University]. 2002, no. 3, pp. 112-122. (In Russian)

48. Comprehensive study on probability of controlling Caspian Sea invasive Ctenophora Activity 4: The laboratory study on probability of controlling Mnemiopsis leidyi by use of Beroe ovata (reproduction study of B. ovata in the Caspian Sea water) Iranian Fisheries Science Research Institute. Report. Tehran. Iran 2007.