**3.** *Mnemiopsis leidyi* **problem in the Caspian**

In the early 1980s, the comb jelly *Mnemiopsis leidyi*, a ctenophore that normally resides off the eastern United States, was accidentally introduced into the Black Sea via ballast waters from cargo ships. This voracious zooplanktonic predator (with extremely high rates of reproduction and growth) reached enormous biomass levels (a few hundreds million tons for the entire basin!) devastating the pelagic (i.e. in water column) food chain in the entire Black Sea basin by the end of 1980s (Vinogradov et al., 1989). Inevitably, such high biomass of this comb jelly consumed a considerable fraction of the zooplankton that had been the food for pelagic fish and their larvae before its arrival. One of the dramatic consequences of the *M. leidyi* invasion was the sharp drop (from about 630,000 tons in 1988 to steadily 150,000 tons in 1991) in commercial catches of planktivorous fish (mainly the anchovy Engraulis encrasicolus L.) in the Black Sea (Kideys 1994; Prodanov et al., 1997). The yearly economical damage to the fisheries sector alone were estimated to be about 250-500 million USD during this period. Although merely one or two researchers pointed out the overfishing as the major cause, the concurrent sharp decrease in zooplankton quantity from different regions in the Black Sea (Kovalev et al., 1998; Gubanova et al., 2002; Gordina et al., 2004) was a conclusive evidence. Indeed one would expect much higher quantities of zooplankton (due to decreased predation) at low levels of planktivorous fish occurence. The decreased levels of the pelagic fish must have also affected the abundance of top predators (several species of predator fish as well as the three species of dolphins) in the Black Sea. Although there are no systematic data on dolphins, they were noted to be scarcer by fishermen and mariners at this period.

*M. leidyi* did not only affected the quantity of animals but also of plant organisms, known as phytoplankton. These (mainly) photosythetic organisms are the food for zooplankton. Due to decreased levels of zooplankton, phytoplankton had a chance to over-grow in the Black Sea (Yunev et al., 2002) during the peak period in *M. leidyi* quantity. Such increase was deleterious particularly for some shallow regions in the Black Sea ecosystem (e.g. off Danube River) already badly suffering from eutrophication.

The situation in the Black Sea has been one of the most striking examples in marine bioinvasion history. Due to scale of the problem, UNEP intervened and gathered international experts in Geneva in 1994, for investigating methods for solving this problem (GESAMP, 1997). The futility of physical and chemical methods for this problem were noted and therefore, biological control seemed the only workable remedy. And, based on the literature knowledge of feeding specificity, another ctenophore species (*Beroe ovata*) rose as the best candidate for dealing with *M. leidyi* problem. Indeed, B. ovata reported feeding only on other ctenophore species (Kremer and Nixon 1976), most notably on *M. leidyi*. However, scientists from the Geneva meeting could not stress on using a new predator species for

*Mnemiopsis leidyi* Invasion and Biodiversity Changes in the Caspian Sea 177

*Mnemiopsis leidyi* - is the lobate ctenophore. Two oral lobes are derivatives of the ctenophore body (spherosome). Four smaller lobes -auricules are situated under the principal two oral lobes. During their movements the lobes in fold completely its buccal orifice. The oral lappets carry tentacular rings. Its central part is situated above the lips of the mouth crevice.

*Mnemiopsis leidyi* photo by

ROOHI, A.

**Luminescence-** *Mnemiopsis* is remarkably phosphorescent. The seat of the phosphorescence

**Origin:** North American species might be brought into the Black Sea with ballast water by Russian tankers driving oil to the ports at eastern coast of USA. From the Black Sea Mnemiopsis might be transferred into the Caspian Sea also by tankers driving oil though the

**World distribution:** The native habitat of the ctenophore, *Mnemiopsis*, is in temperate to subtropical estuaries along the Atlantic coast of North and South America (Harbison et al., 1978). In the early 1980s, it was accidentally introduced to the Black Sea (Vinogradov et al., 1989), where it flourished and expanded into the Azov, Marmara, eastern Mediterranean, and Caspian Seas (Studenikina et al., 1991, Shiganova et al, 2001a, Shiganova et al, 2001b).

Both "lips" are extremely contractible (Agassiz, 1860; Seravin, 1994, plate 3).

et al., 2008a, b)

**4. General aspect of** *Mnemiopsis* 

*Mnemiopsis* **characteristics** in a glance are as follows:

Plate 3. *Mnemiopsis leidyi* images of the Caspian Sea

is confined to the rows of locomotive flappers.

**Ecological group-** Macrozooplankton

Volga-Don Canal.

obtained via remote sensing display the Caspian Sea as one of the most eutrophic regions in the world in recent years, in contrast to years before *M. leidyi* invasion (Roohi

dealing with the problem in the Black Sea, due to risk of unexpected problems: What if *B. ovata* start feeding on other species rather than *M. leidyi?.* 

A warning that *M. leidyi* might also invade the Caspian Sea had been voiced during the Geneva meeting as well as by Dumont (1995). Unfortunately, at the end of the 1990s the invasion of *M. leidyi* in the Caspian Sea was already being reported (Esmaeili et al., 2000; Ivanov et al., 2000; Roohi, 2000). It must have also been transported in the ballast waters of ships traveling from the Black Sea (salinity 18 ppt) to the Caspian Sea (max. salinity 13-14 ppt) through the Volga Don Canal. Investigations in the Caspian Sea showed by September 2000, it was found everywhere including the northern Caspian where the salinity can be as low as 4 ppt (Shiganova et al., 2001a).

The impact of *M. leidyi* on the Caspian Sea ecosystem has been even worse than in the Black Sea due to the greater sensitivity of this enclosed basin. Adverse impacts from *M. leidyi* could be listed as the following:


obtained via remote sensing display the Caspian Sea as one of the most eutrophic regions in the world in recent years, in contrast to years before *M. leidyi* invasion (Roohi et al., 2008a, b)
