Use of Beroe Ovata to control Mnemiopsis populations in the Caspian Sea

As far back as the 1990s the scientists put forward actions on biological control of Mnemiopsis in the Azov Sea and the Black Sea basin (Harbison, Volovic, 1993). A number of actions recommended as well were on preservation of some native species capable of feeding on Mnemiopsis as well as on implementation of adequate studies and acclimatization of obligate predators of Mnemiopsis – another comb-jelly (Beroe Ovata) and a number of fish species, including Pampans (?), Beroe Ovata, Peprilus triacanthus and P. Paru. Beroe and Pampans, inhabiting the natural habitat of Mnemiopsis are highly effective in suppressing the outbursts of the latter.

The cost of works on biological control over distribution of Mnemiopsis in the Azov Sea and the Black Sea basin was evaluated at some millions of dollars or at 1-1.5% of the annual damage sustained merely as a result of the loss of catch. Ideas expressed and a strategy program in general were supported by the experts of countries – participants of the II technical consultation held in the framework of General Fisheries Council for the Mediterranean (Ankara, February 1993), joint group of experts of FAO, UNESCO, UNEP and other UN Organizations on scientific problems of marine environment (GESAMP Reports and Studies, No. 58, 1997), VIII session of Russian-Ukrainian Committee on fishery in the Azov Sea (Kerch, 1998). However, up to now none of the actions (apart from monitoring of ecosystems, Mnemiopsis populations distribution included) were implemented by the littoral countries of the Black Sea.

In 1997 a new invasive specie – comb-jelly Beroe ovata – was discovered in the Black Sea (Zaytsev, 1998). The specie was one of the organisms recommended earlier for introduction in the Azov Sea and the Black Sea to suppress distribution of Mnemiopsis. Studies on a number of adaptations of Beroe as well as observations of distribution and dynamics of Mnemiopsis and Beroe population in the north-eastern part of the Black Sea gave way to a number of important conclusions (Shiganova et al, 200, Volovik, 2000) including as follows:

• Beroe Ovata is capable of tolerating low salinity of water and could acclimatize water area with salinity over 7.5%, i.e. practically the entire area of the Azov Sea and the Black Sea; a lower limit of salinity tolerance by Beroe is between 7% and 4%

• Under experimental conditions Beroe ovata ate only comb-jellies Mnemiopsis and Pleurobrachia;

• Beroe ovata is really capable of suppressing distribution of Mnemiopsis in the Azov Sea and the Black sea basin in an effective way;

• Populations of Mnemiopsis in the joint habitats with Beroe have reduced by ten times as compared to the year with favorable conditions of environment but no Beroe present.

By 2000 observations of the Azerbaijan Scientific-Research Institute on Fishery of the ecosystems of the Azov Sea and the Russian part of the Black Sea with distribution of the populations of comb-jellies and fish-planktoprotobes made it possible to state as follows:

• populations of Mnemiopsis in Kerchian strait during spring period were at extremely low level with this causing its late outbursts in the Azov Sea and biomass being relatively low: 1999-36 mln t, 2000 – 15 mln t;

• up to middle/late July favorable feeding conditions for planktoprotobes were observed in a greater water area of the Azov Sea (biomass of zooplankton varied from 1524 mg/m³ in May, 287 mg/m³ in July to 50 mg/ m³ in August, i.e. it was twice more stable as compared to the relevant months of the years precedent);

• populations of the Azov khamsa and sardelle by the autumn 2000 had the best figures of physiological state as compared to the years precedent, in particular oil quantity at the end of fattening period amounted to 17-19% of khamsa, 21-24.5% - of sardelle as compared to 12-15% and 15-17% relatively of the years precedent.

• during fishing season in 2000/2001 total admissible catch of khamsa and sardelle has been determined at 10000 and 40000 correspondingly, i.e. by 2-3 times higher than in the years precedent.

Thus, appearance of Beroe Ovata in the Azov Sea and the Black Sea basin (the natural habitat of this invasive specie has not been yet precisely determined) has contributed to the development of the situation in the Azov Sea in compliance with the scenario of late entering of Mnemiopsis. (Volovik et al, 1991, Comb-jelly…, 2000) which allows to partly restore the possibilities of maintaining fishery on the Azov Sea and the Black Sea mass planktoprotobes, however, not liquidating fully the problems of biological control over development of Mnemiopsis population in the Azov and the Black Sea zone as well as those of re-establishment of catch volumes for khamsa, sardelle, scad and other fish.

In the meantime, there is still a hope to succeed in solving the problem of destruction of pelagenic part of the ecosystem by the comb-jelly Mnemiopsis as applied to the Caspian Sea, the Azov Sea, Black Sea, Marble Sea as well as other seas of the Mediterranean basin based on strategic actions published earlier (Harbison, Volovik, 1993). Information available enables to state that the most effective counteraction for Mnemiopsis is introduction of obligate predator(s) with compatible potencies of reproduction and tolerance towards environment which characterize Mnemiopsis.

The following properties make Beroe ovata the most preferential predator:

• low salinity tolerance (the lower tolerance threshold of Beroe is between 7.2-4.5%, and that of Mnemiopsis – approx. 3%). Since Mnemiopsis penetrates into the Azov Sea every year, causing outburst and dying during autumn-winter period, the major area of fighting it is water area of the Black Sea, which, if judged by salinity tolerance, could be totally acclimatized both by Mnemiopsis and Beroe.

• Reproduction of Beroe begins when its body is 2.5-3.0 sm at the age of one month, fertility of puberal individuals makes up several thousands of ovum daily (like Mnemiopsis)

• Beroe is an obligate eater of comb-jellies (Mnemiopsis and Pleurobrachia);

• The events of 1997-2000 proved that Beroe succeeds in surviving in conditions of the Black Sea round the year just like Mnemiopsis, i.e. there always exists a possibility of preservation of the population (female culture).

Information on development cycles of Beroe and Mnemiopsis in a natural habitat as well as observations on biology of invasive species in the Azov and the Black Sea basin enable to formulate the following statements predetermining effective use of Beroe as a regulator of Mnemiopsis populations in water basins-recipients:

• prompt and positive effect – sharp reduction of the populations of Mnemiopsis takes place when Beroe is numerous (irrespective of the fact whether the majority is presented by large specimens or whitebait);

• similar dynamics of the populations of comb-jellies under studies is preserved in natural habitats and water basins of introduction: first Mnemiopsis sharply increases its populations, reaching maximum figures, then close to that maximum level there appear outbursts of Beroe which eats away Mnemiopsis within 3-4 weeks.

During the period of March 1999-September 2000 the following observations were made in the north-eastern part of the Black Sea:

• during the period when Mnemiopsis increases its population to maximum it destructs the community of zooplankton reducing its biomass by ten times.

The statements set forth enable to make the following assumptions:

• during the period of intensive development of Mnemiopsis and increase in number of its population Beroe is either few or its natural habitat does not coincide with Mnemiopsis, or temperature and other conditions of environment do not contribute to increase of Beroe in number or all these factors take place in various combinations and proportions;

• intensive development and increase of Mnemiopsis in number could be controlled by comparing artificially the period of development of Mnemiopsis and Beroe populations. To implement the latter female culture (of puberal individuals) and planting material of Beroe (ovum, larvae, whitebait) should be always available.

And this in its turn predetermines the basic demand towards scientific and industrial work with regards to Beroe in connection with the problem of biological control over development of Mnemiopsis population in the Azov and the Black Sea basin, i.e. the demand is to keep a size-limited population of Beroe in artificial conditions and be capable of getting enough quantity of certain planting material, i.e. to create biotechnology of industrial cultivation of Beroe.

There exist all prerequisites for creation of industrial biotechnology to cultivate Beroe in the Russian part of the Azov-Black Sea zone, and those are as follows:

• Azerbaijan Scientific Research Institute for Fishery possesses a unique method on development and introduction of biotechnology for industrial cultivation of various objects (fish, mollusk, crustaceans) aimed at stocking of naturally impounded bodies with fish and maintaining fish stock as well as aimed at producing commercial goods under conditions of specialized economy;

• Azerbaijan Scientific Research Institute employs qualified staff of hydrobiologists, ichthyologists, fish farmers as well as other specialists having been involved in creation of biotechnology for intensive commercial growing of fish (Acipenseridae, pipe perch, Cyprinidae, sheatfish), hydrobionts (mollusks, mussels, crawfish) and their forage objects;

• On Bolshoy Utrish Cape (50 km to north-west of Novorossiysk Port) there operates a Scientific and Experimental Marine Biotechnological Center “Bolshoy Utrish” which is a State-run unitary institution including a Section with incubatory and fish farming facilities (reservoirs), laboratories and other structures. However, the whole complex is out of service and requires reconstruction with the latter being of urgent need for water supply systems. In compliance with the data held by Azerbaijan Scientific Research Institute for Fishery the least polluted part in the area of Bolshoy Utrish at the moment is a less man-damaged part of water area of the Black ea. Location of “Bolshoy Utrish” base is a possibility, when necessary, to produce forage objects for Beroe on a round-the-year basis, and i.e. at least comb-jelly Pleurobrachia.

Thus, objectives put forward (creation of water complex and biotechnology for cultivation of Beroe) could be achieved within a short period of time (approx. 2-3 years) which is a really short term for such objectives.

To be resolved apart from development of biotechnology on cultivation of Beroe directly shall be a secured supply of artificial population of Beroe with feed with this further requiring additional funds to study the possibilities of preservation of comb-jellies Mnemiopsis, Pleurobrachia and their feed organisms in artificial conditions. In principle biotechnology of similar activities is known and required at the moment is a new challenging but manageable task – its adaptation for other live objects.

As it was earlier mentioned in 1999 Mnemiopsis was discovered in the Caspian Sea. The comb-jelly has become a mass organism by 2000, acclimatizing almost 80% of the water area of the sea by late August. It is natural that the issue of introduction of Beroe Ovata into this basin should be studied as well. However, the following circumstances are to be taken into account:

• saline composition of the Caspian water significantly differs from “regular” sea water as well as waters of the Black Sea and the Azov Sea (Zenkevich, 1963). This will require implementation of special studies on tolerance of Beroe to Caspian water;

• in case if Beroe could inhabit Caspian water, the problem of artificial elimination of divergence between the development peaks of populations of Mnemiopsis and Beroe should be solved as well;

• an experiment was carried out on keeping Beroe in water with Caspian salinity of 12%: Beroe lived for two days and the experiment was then stopped. This inspires the hope the activities in this direction are necessary.

• Unlike the Black Sea, there exist no native organisms in the Caspian Sea, which in case of the lack of Mnemiopsis in isolated regions of the Caspian, could be a feed for Beroe, thus contributing to stability of the population of the invasive specie in this basin. Under such circumstances a regular renewal of the “Caspian” Beroe population from outside will be needed (renewal rates and frequency are to be specified);

• It’s necessary to study specifically which stages of the development of Beroe are the most appropriate ones for the comb-jelly to be transported in order to get maximum effective results with minimum expenses involved.

Thus, the project suggested is aimed at control of exotic specie Mnemiopsis in the Azov Sea, Black Sea and Caspian Sea, restoration of productive capabilities of their pelagic zone and its traditional food chain, significant increase (no less than by 3-5 times on the Azov sea and by 2-3 times on the Black Sea) of catch of mass fish-planktoprotobes as well as at preservation of unique ecosystems and their biota in the mentioned seas.

When touching upon the issue of control of exotic organisms in the Azov-Black Sea and the Caspian basins it’s most unlikely to miss an opportunity on evaluation of the utilization of earlier mentioned fish-pampan for this purpose. According to Dr. G. R. Harbison (Woods Hole University, USA-personal communication) he has studied adaptation of whitebait of these species during vegetation season. The studies proved that these fish inhabit water with up to 35% of salinity and feed on gelatinous plankton. Due to high growth rates and special meat these objects are considered not only as predators of the comb-jellies under conditions of the mentioned marine basins, but also as objects of marine culture. However, through the lack of scientific information these issues have not been duly studied.

This report should be deemed also as an appeal to the scientists of the Caspian region for participation in a fund-raising procedure with regards to the activities described above.

References:

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