Abstract
The introduction and spread of non-indigenous species may have ecological, environmental and economic impacts where they invade. This work aims to study the morphological characteristics, the quantitative variables, the possibility of coexistence with other native species and the pathways of introduction of non-indigenous cladoceran Evadne nordmanni (Lovén, 1836) in the middle part of the Caspian Sea. Ballast water is a possible vector for the introduction of cladoceran Evadne nordmanni into the Caspian Sea. The abundance of Evadne nordmanni in all surveyed areas reached an average of 799 individuals/m3. Its biomass was 257.58 mg/m3. Evadne nordmanni significantly contributes to the abundance and biomass of zooplankton in the Middle Caspian Sea. The proportion of the dominant calanoida Acartia tonsa decreased from 71–90% to 40% with the appearance of Evadne nordmanni. Further investigations are needed to analyze the responsible route of Evadne nordmanni introduction to the Caspian Sea and its consequences on biodiversity; since this species is a predator and could have consequences on the feeding conditions of planktivorous fish in the Caspian Sea.