Development and interaction of ctenophores <i>Beroe ovate</i> Bruguière, 1789 and <i>Mnemiopsis leidyi</i> A. Agassiz, 1865 in the coastal zone of the Middle Caspian Sea

Aim. Analysis of the distribution and status ctenophores В eroe ovata Mnemiopsis leidyi , assessment parameters their interaction in Middle Caspian Sea. Material Methods. The material was obtained western eastern parts Sea September–October 2022. Large were collected using a big cone plankton net with 0.5 m 2 opening 500 μm, mesh size. number size large determined immediately after collection, larvae eggs counted samples fixed formalin to final concentration 4%. Zooplankton by Juday (0.1 opening, 180 μm size). Results. In September‐October 2022, developed population active reproduction recorded waters habitat area B. has significantly expanded north compared 2021. Complete suppression Beroe observed on most shelf, as well. total reached 48 ind/m biomass – 12 g/m . Single individuals found at salinity 5.7 psu. structure mesozooplankton still dominated small copepod Acartia tonsa Conclusion. New data indicate development Sea, which presents fundamental challenge for restoration ecosystem. progressive adaptation conditions led its expansion areas low salinity. A complete M. Leidyi new alien noted shelf indicates an increase pressure corresponding period