First record of the non-native species Beroe ovata Mayer 1912 (Ctenophora: Nuda) in the Caspian Sea

A new non-native ctenophore species, Beroe ovata, was recorded for the first time in the southern Caspian Sea on 13 November 2019 during a regular plankton sampling program. Considerable aggregations (1-5 individuals/m3) of B. ovata were found near an aquaculture site for fish cage, about 8.5 km offshore. The arrival of B. ovata, a non-native ctenophore predator for the Caspian Sea, has been much anticipated since the arrival of its prey, another aggressive ctenophore Mnemiopsis leidyi in the late 1990’s. The adverse impact of M. leidyi has been devastating since its appearance on the Caspian Sea, causing unprecedented decreases in mesozooplankton biodiversity and biomass, resulting in a collapse of fisheries on small pelagics. The occurrence of B. ovata in the Caspian Sea is of significant interest for scientists, environmental managers and other stakeholders like fishermen since this new invader had already shown its ability to help in recovery of the fish stocks and ecosystem in whole in the Black Sea. Based on the outcomes of intensive field and laboratory studies in these neighbouring seas, we could suggest that the arrival of B. ovata also will result in the recovery of the Caspian Sea ecosystem.