New data on the ctenophore <i>Beroe ovata</i>, an invader to the Caspian Sea

Abstract

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.

Keywords

• caspian sea
• ecosystem
• ctenophores
• <i>mnemiopsis leidyi</i>
• <i>beroe ovata</i>