Assessment the effects of Mnemiopsis leidyi on ecosystem functioning in southern part of the Caspian Sea

In recent decades, due to changes of water level in the Caspian Sea, the entering of environmental pollutants and especially invasive ctenophore species, the ecosystem structure of the Caspian Sea has changed dramatically. In this study, the effects of the invasive ctenophore of Caspian Sea on the ecosystem performance in the Iranian coasts of the Caspian Sea, using the data of catches and reserves of important fish species during the first three periods were studied; before the ctenophore full expansion (1996-2000, reference period), second (2001-2006) and the third (2007-2016), after the development and spread of ctenophore in the Caspian Sea. The results showed that the total catch of fish in the Caspian Sea increased from about 75,000 tons in 1996 to about 115,000 tons in 1999, but in 2003 it decreased sharply to about 32,000 tons. The main factor increasing and then reducing the composition of the fishing in different periods were kilka fish. The amount of bony fish catches was increasing slowly, and Whitefish and Mullet were the main cause of these changes. Sturgeon catches were also decreasing in all three periods. The reserves of the two species of Anchovy Kilka and the Clupeonella grimmi (especially during the third period) were severely degraded. The reserves of two species of Whitefish and Golden-grey Mullet were first increased and then decreased. This assessment demonstrates the dramatic change in ecosystem performance. The ecosystem s performance was changed according to the amount of catches and according to the amount of storage from the class of without effect (E0) in the first period to the classes of weak and moderate effects (E1, E2). The elimination of the two key species (Anchovy Kilka and Clupeonella grimmi) can be a major contributor to the sturgeon and Caspian Seal deposits. In the first and second periods, due to the restoration of favorable conditions for the further expansion of fish stocks, the reserves of the two species of Whitefish and Golden Mullet increased and then declined at the end of third period.

کلیدواژه ها:

Ctenophore ، Hunting ، Reserves ، Fish ، Ecosystem Function ، Caspian Sea