Control Copepod Abundances and Kilka Catch by Invasive Predator Mnemiopsis leidyi A. Agassiz, 1868 in the Southern Caspian Sea

Abstract

The Caspian Sea has a variety of species and groups of aquatic animals, e.g., plankton and fishes that are exploited, unfortunately in the past decade, this sea has entered and expelled of some non-indigenous species such as ctenophore Mnemiopsis leidyi, Copepods Acartia tonsa, Balanidae Balanus improvisus and Mullets Lisa saliens have caused major changes in the Sea. One of the species got common in the coastal waters is M. leidyi with the highest biomass in summer at the temperature of 25-30 °C, and the highest abundance was observed in autumn while the minimum density was in winter of 8-10 °C. The ctenophore distribution of length frequency indicated that while 83% of the population consists of larval and immature organisms, only less than 17% belonged to the adult group in the costal waters of the Caspian. The largest size of the jelly was 70 mm long in the southern Caspian Sea in September 2002. Based on the jelly food consumption, the Nauplius, copepodites and adults of Acartia tonsa consisted 66% and bivalves was 13% in the Caspian. Therefore, it seems the reduction of the comb jelly compared to its early year's invasion was due to the reduction of edible zooplankton especially A. tonsa in the southern of the Caspian Sea. During 2001-2013, Kilka catches amount was decreased to ~15000 kg from 95000 kg in 1996 with the changes of Clupeidae species composition of Clupeonella engrauliformis to C. cultriventris caspia.