The invasive ctenophore Mnemiopsis problem in the Black and Caspian Seas

Figure 1. Mnemiopsis from the Black Sea.

In the 1980s, the introduction of a new species (a lobate ctenophore, Mnemiopsis leidyi or M. mccradyi) (see Fig. 1) into the Black Sea radically affected the whole ecosystem (Vinogradov et al., 1989; Kideys, 1994). 

This species had a negative impact on the most dominant fish of the Black Sea, the anchovy Engraulis encrasicolus, through competion for the edible zooplankton as well as consumption of anchovy eggs and larvae. The mass occurence of Mnemiopsis was one of the most important reasons for the sharp decrease of anchovy and other pelagic fish stocks in the Black Sea (Kideys, 1994; Kideys et al., 2000; see Fig. 2). Due to scale of the problem, UNEP has been involved in order to find a solution for the impact of Mnemiopsis on the Black Sea ecosystem (GESAMP, 1997).

Meantime, the possibility of its introduction into other neighbouring sensitive ecosystems, notably the Caspian Sea, has been mentioned (Dumont, 1995; GESAMP, 1997). However, another ctenophore, Beroe (either ovata or cucumis, which is a subject of debate), wich arrived in the Black Sea in late 1990s, seemed very effective predator on Mnemiopsis (see Fig. 3). Several laboratory and field data suggest that Beroe feeds exclusively on Mnemiopsis in the Black Sea (Finenko et al., 2001).

Figure 2. The relationship between Mnemiopsis biomass (red) and anchovy catch (blue) in the Black Sea (updated from Kideys et al., 2000).

Arrival in the Caspian Sea

As expected, the Mnemiopsis ctenophore was reported from the Caspian Sea by November 1999 (Ivanov et al., 2000). However, Iranian fishermen noticed Mnemiopsis first time in 1998 summer (pers. comm. with Hasan Fazli, Mazandaran Fisheries Research Center, Sari, Iran). To catch three species of kilka, Iranian fishermen sish at night using a funnel net and a light. Mnemiopsis would be very easily recognised using this method, so we can safely assume that the occurrence of this ctenophore in noticeable numbers dates from 1998 for the Iranian waters of Caspian Sea. 

Ivanov et al. (2000) suggested that this ctenophore was transported with ballast water taken aboard in the Black Sea or the Sea of Azov (where Mnemiopsis occurs in warm months) and released after ballast-loaded ships passed through the Volga Don Canal and the shallow, freshwater North Caspian Sea, into the saltier Central or South Caspian (Ivanov et al., 2000).

The impact of Mnemiopsis on the ecosystem of the Caspian Sea is already very significant. Preliminary results from monitoring programs set up in Azerbaijan and Iran clearly show that zooplankton seems to be the worst-affected component of the ecosystem in the Caspian Sea (Kideys et al., 2001a,b). The impact on lower trophic levels has been, so far, appropriately reflected by the higher trophic levels. Pelagic landing figures pointed to about a 50 % reduction for the Iran and Azerbaijan fishery (Kideys et al., 2001a,b). Similar values were presented by Russia with respect to fishery. There have also been lower pregnancy figures, higher mortalities and consequently decreases in endemic Caspian Seal populations recently (Shiganova et al., 2001).

Figure 3. Black Sea Beroe.

Seeking a solution

The Caspian Environment Programme (CEP) located in Baku, Azerbaijan, has organised very fruitful activities aimed at defining, stating and proposing a solution to the Mnemiopsis problem in the Caspian Sea, with the help of riparian countries and Mnemiopsis experts from different countries. Among the activities were two meetings organised in Baku specially to discuss Mnemiopsis. These meetings resulted in the setting up of ecosystem monitoring programmes, with particular reference to Mnemiopsis, on Azeri coasts (supported by European TACIS Programme) and in two different regions of the Iran coast in the Caspian Sea (with the support of the Iranian Fisheries Organisation, Shilat). In addition to these, a few basin-wide surveys were taken by the riparian countries to assess the ctenophore distribution in the entire Caspian (Shiganova et al., 2001; Kideys and Moghim, 2002). 

Experiments

One of the most important activities, howevwe, has been laboratory experiments with Beroe that were transported to an Iranian laboratory (Sari) on the Caspian (Kideys et al., 2001c); special thanks to CEP and Shilat for supporting this important activity. In these experiments, the adaptation and survival of Beroe, and its miscellaneous physiological characteristics (feeding, spawning, respiration), were measured in Caspian water conditions. Thus, for example, we now know the diet and feeding rate of Beroe on Caspian Mnemiopsis. During these experiments, different physiological aspects of Caspian Mnemiopsis were also successfully studied (Kideys et al., 2001c). 

The research goes on

We, as a group of scientists, are at present continuing our experiments to assess the impact of Mnemiopsis and its control using Beroe.

Bibliography

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