As a result of 30-year integrated studies, the Russian scientists have significantly succeeded in understanding the mechanisms determining the Black Sea ecosystem. Today they can, with a certain degree of probability, forecast changes in the life of this basin. The obtained results in many respects explain the peculiarities of operation of the ecosystems of other internal seas and the World Ocean as a whole and form the basis for efficient use of its resources. Deputy Director of P. Shirshov RAS Institute of Oceanology Mikhail Flint, Dr. Sc. (Biol.), told our correspondent Yevgeniya Sidorova about this.

- Mikhail Vladimirovich, what problems do researchers of the Black Sea face today?

- One of the main problems is to learn to reliably distinguish between the consequences of man's activity and those of climatic changes. This is fundamentally important for understanding both life of other internal seas and the World Ocean as a whole.

Against the background of lasting global climatic trends in the sea ecosystems there are 10 - 20-year fluctuations the information about which has practical importance for the living generation that is obliged to adapt its activity to them. Now periodic fluctuations have definitely become stronger*. We try to link the effects of general atmospheric circulation and changes in regional climate, understand how the latter influence the state of sea ecosystems, their productivity and biological diversity. However, we have not succeeded in finding out the initial cause of "climatic reshuffle" yet.

* See: Yu. Israel, "Threat of Climatic Catastrophe?", Science in Russia, No. 4, 2004. - Ed.

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ABOUT THE CONSEQUENCES OF WARM WINTER

- How does the Black Sea ecosystem react to climatic surprises?

- In order to have an idea about the reaction of the ecosystem, one has to understand well what processes take place in it in winter. And that's why. In the Black Sea there is breaking of water layer: the water flowing in through the Bosporus Strait and having the higher density goes down, while the effect of fresh river inflows prevails in the upper part (they amount to 350,000 km³ annually). The salt content in superficial layers is 16 - 17%o, while in mean depths-22%. In the central part of the Black Sea hollow at the depth of 100 - 200 m (depending on the area) there is an upper bound of hydrogen sulphide contamination zone, and living organisms, except for bacteria, can exist only above it-in an oxygenous zone. The volume of the latter is so small compared to the size of the whole basin that any changes, be it climatic, man-made or as a part of biota, have notable effect upon the whole community.

In summer the upper layer of the Black Sea water warms up to 22°C, while in winter it cools down to 5.5 - 6°C, its density changes accordingly. A process of winter vertical convection starts affecting, on the average in the basin, the upper 70 - 100-meter formation: heavy, cold, oxygenated water goes down to the zone contaminated with hydrogen sulfide, creating conditions for its oxidation, while deep water, relatively warm, light, enriched with biogenic elements goes up, providing planktonic waterweeds with nourishment for the next season of vegetation.

The described downward movements of water in the Black Sea are limited by a sharp difference in density, which results in creation of the so-called intermediate layer with the temperature of 5.5 - 8°C, which is an integral characteristic of climatic conditions in the region. In warm years with weak winter convection less oxygen shall enter deep layers and hydrogen sulfide which was not exposed to oxidation shall approach the sea surface. It should be noted that the depth of oxygen zone in the Black Sea amounts to, on the average, about 120 m (over the continental slope it shall increase, while it shall decrease to the center of the basin). Therefore, the rise of its lower boundary even by 10 - 12 m (which can be seen under modern climatic conditions) means the decrease of "volume of life area" in the basin by 10 percent.

CONDITIONS FOR INTERRELATION AND ISOLATION

- You've mentioned that the results of the researches in the Black Sea let better imagine the life of other internal seas. However, there is no hydrogen sulphide layer there.

- Nevertheless, in terms of the Black Sea one can visually see interrelation between changes of climate and peculiarities of the intra-basin circulation taking place in other internal seas and mid-ocean. The mechanism about which I'll tell you has several aspects of influence upon the Black Sea ecosystem.

Thanks to the information from satellites, mainly about dynamics of water temperature and content of vegetable pigments in the superficial layer of the Black Sea, we have obtained an idea about intra-basin circulation which has two polar versions-contour and vortical. The first, as a rule, prevails in cold years with strong wind influence: a powerful circular stream is formed which results in isolation of coastal and shelf zone heated from the relatively more cold central basin. A vortical type of circulation is formed during the periods of weak winds, which results, on the contrary, in complete mixing of sea waters.

Bathymetric map of the Black Sea. (The map was drawn by R. Stanichnaya from the Marine Hydrophysical Institute of the National Academy of Sciences of Ukraine.)

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Types of circulation of the Black Sea active layer: A - with a strong wind influence upon the basin; B - with a relatively weak wind influence upon the basin.

Here it is worth mentioning that the main consequences of man's influence upon the sea ecosystem (recreational, transport and others) are concentrated in the Black Sea shelf, the width of which in the Russian sector does not exceed 5 - 7 km. Moreover, accumulation of contaminants, namely, heavy metals (plumbum, cadmium, copper, zinc) coming with river flow and aeolian transportation takes place along the shore. These components are concentrated in a thin superficial film of water and are sublimated with strong wind, creating a rather unfavorable situation at health resorts. Of course, all negative development processes of man-made pressing become stronger with the contour circulation.

It is important that the change from contour circulation to the vortical one results in ventilation and cleaning-up of the coastal zone. Then one can see contaminated streams at the distance of dozens of kilometers from the coast moving away from it with speeds (40 - 70 cm/sec), which are rather high for such a basin. Concentration of heavy metals in the superficial water film of these contaminated flows can increase the background values by 1.5 - 2 times. Fortunately, a considerable part of pollutants brought out to the basin central parts shall be buried in hydrogen sulphide zone.

Knowing these mechanisms, man can minimize his negative influence upon the Black Sea ecosystem. Today specialists can specify the time and place in a shelf favoring a fast change and release of coastal zone from contaminants. Also, there are isolated areas, which are not inclined to cleansing up at any climatic and wind situations. When planning economic activities, one needs to take this circumstance into account. As you see, fundamental scientific researches can give an important practical result.

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Variations of average winter air temperature and water temperature in a cold intermediate layer (CIL).

- Indeed, advance information about the ability of the coastal zone to natural cleansing is extremely important. Moreover, when it is a question of the Black Sea ecosystem whose economic and recreational importance grows.

Is there any information about the effect which intra-basin circulation has upon thalassophiluses?

The biological productivity of the ecosystem depends on the nature of circulation. Thus, in the periods with weak wind influence and intensive water exchange between the shelf and deep basin the larvae of benthic organisms capable to develop in full only in shallow waters are brought out to the central part where after settling down they get into the hydrogen sulphide zone and are lost. The narrower is the shelf, the more intensive is the process. We believe that such "sequestration" of benthic population with a certain type of circulation must be observed not only in other internal seas (which do not accumulate hydrogen sulfide at the bottom) but also in the ocean with narrow shelf: larvae living at the depth of not more than 100 - 150 m cannot develop at the bottom under the pressure of 2-km water layer. However, say, in the Caspian Sea with an evenly wide shelf this process is not so important for the ecosystem operation.

- Therefore, we also deal with negative developments of vertical circulation, don't we?

- There is no simple answer whether the influence of the mentioned type of circulation upon the Black Sea ecosystem is favorable or negative. Indeed, a considerable part of larvae of the benthic invertebrates forming natural biofilter in the sea coastal zone are lost. However, a considerable part of the larvae of predacious mollusc Rapana, which had lethal effect upon benthic population of the Black Sea are also lost. I'll say more about it later. Moreover, one should remember about the ventilation of the coastal zone which I have mentioned.

UNDER THE POWER OF INVADER SPECIES

- You have revealed the main aspects of influence of the climatic factor upon the Black Sea ecosystem. What about mollusc Rapana which has played a fateful role in its life?

- Our researches have shown that the appearance of a number of new species in the Black Sea in a short period of time resulted in such fundamental changes which no modern man-made factor could initiate. Had we not studied the mechanism of these transformations, we could have come to wrong conclusions.

Just imagine: the largest gas pipeline "Goluboi Potok"* is under construction, we monitor it, evaluate ecological damage and find a great number of lost molluscs in the control area within the territory located in affected area of the gas pipeline. The beach is covered with their clamshells. A person not informed about it would say: here a disaster took place and the gas pipeline is to blame. However, the source is in mutual relations inside the ecosystem which partly relate to climatic changes.

- However, the appearance of alien species in the Black Sea is likely to be man's handiwork, isn 't it?

- Predacious gastropod Rapana venosa, a dweller of the Yellow Sea, was brought here in 1947 by the Soviet torpedo boats that arrived from Port Arthur (Liishun). Having been discharged together with ballast water, it found itself in the habitat which was new for it and settled down.

- It is most unlikely that the Far Eastern ships did not call at the Black Sea earlier. Why then did the mentioned species settle down here exactly in the 20th century?

- Apparently, Rapana adapted thanks to successful concurrence of circumstances: the mollusc was brought at a certain stage of development and relevant season.

* Sea area of the gas pipeline "Goluboi Potok", 396 km long (from the township of Arkhipo-Osipovka, Krasnodar Territory, to Durusu terminal 60 km from Samsun, Turkey) was built from September 2001 to June 2002 - Auth.

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- That is, the man's deed doing was "supported" by natural environment. And doesn't Rapana have natural enemies?

- The Black Sea is a quasi-isolated ecosystem communicating with the Mediterranean Sea via the Bosporus Strait. If one had to fill the Black Sea hollow through this strait, it would have taken about 2,000 years, that is, the connection with the World Ocean is very weak. (If you like, we had the same situation with Rapana, as was the case in Australia with the Dingo dog which had been first brought there by people over 3 thousand years ago). The mollusc killed practically all oyster plantations, destroyed coastal habitations of mussels which played the role of natural biofilter (by the way, in Bulgaria they even tried to implement the idea of creating mussel plantations in the places of man-made contamination of water areas for their clean-up).

At the end of the last century in the Black Sea there appeared another invader species which played a negative role in the ecosystem-comb jelly Mnemiopsis leidyi, an exceptionally gluttonous predacious organism. They assume that it was brought together with ballast waters from the Atlantic Ocean in 1982. It took it several years to adapt, and these were not marked by specific climatic characteristics, so its presence in the basin can be regarded as handmade. In 1988 - 1989, the number of Mnemiopsis dramatically increased and, in fact, it destroyed the organisms responsible for productivity of medium and high trophic levels of the ecosystem. Apart from plankton living in the water layer, larvae of benthic animals and fish were its victims. The Black Sea anchovy (or khamsa), which served as a basis for regional fishery, didn't only lose food-zooplankton - but himself became a part of comb jelly's ration. However, there was no factor limiting the reproduction of the latter.

Although in the best years they got 450 - 480 thousand tons of khamsa (at the beginning of "single rule" of Mnemiopsis the catch reduced by more than ten fold). One shouldn't forget that whole areas of Turkey depend on the well-being of this kind of trade, on which a way of life of people and, to a great extent, coastal economy are built. We can see similar situations in other internal seas, too, and they cannot be underestimated. It is fair to say that 2 - 3 years after stoppage of catch of the Black Sea anchovy, its number began to recover gradually despite the presence of the predacious comb jelly. This is very important and means that in the ecosystem free from man-made pressing there are proper mechanisms capable to correct the situation to some extent.

- However, it is known from the publications that now in the Black Sea there is a species limiting the activity of Mnemiopsis.

- In 1998, there appeared another comb jelly invader here - Beroe ovata, feeding on Mnemiopsis (it eats nothing else), and a year later its mass reproduction was noted. This species moved to the Black Sea ecosystem from the Mediterranean Sea, which was promoted by lasting and profound warming of regional climate. Comfortable conditions lasted for rather long, and Beroe population adapted to this biotope so that it did not die at some decrease in temperature. Mnemiopsis seemed to be doomed, however, the real situation proved to be more complicated.

The point is that the optimum conditions for development of this species fall to summer months: its number starts increasing in July, is at the high (up to 1,500 - 2,000 specimens per lm²) in August-September and goes down in October, while it is already difficult to find Mnemiopsis by November-December (we may not find its winter forms because researches were not carried out in the whole Black Sea basin). Seasonal dynamics of zooplankton abundance actually repeats this "diagram". With appearance of Beroe for whose development the warmest possible water was needed (this condition is fulfilled in August-September), an important part of the annual cycle of Mnemiopsis was cut off,

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but as a whole it remained against general expectations. Naturally, in a smaller number.

- Does it mean that the struggle against the sea dweller unwanted by the human being by introducing the species hunting for it is hopeless?

- There is no simple answer to this question, but it is evident that such an ecological experiment is extremely complicated and requires thorough preparation. By the way, in the Caspian Sea there also appeared Mnemiopsis and created a situation which is, in principle, similar to the Black Sea one. There are proposals to settle Beroe there to correct the number of Mnemiopsis. However, one should rememberthat a significant part of the Russian water area of the Caspian Sea is comparatively fresh and freezes in winter, which makes habitat unfit for Beroe development. In cool years in the Black Sea region the reduction in the number of this species immediately takes place, while Mnemiopsis feels better. However, in warm periods the situation recovers. One can forecast that if a lasting period with severe winters begins, the role of Beroe in the Black Sea ecosystem shall be significantly reduced and, theoretically, it can disappear from the basin.

As far as 1 know, modern crisis of the most important species of fishery in the northern part of the Caspian Sea can hardly be defined only by the influence of an invader species. Monstrous illegal pressing is a true reason. Pollution of the Caspian Sea through river flow is also important. The state of this ecosystem is not studied enough, understanding of the mechanisms regulating it lacks, there are no reliable ideas about the influence of climatic factor. However, a mechanistic approach to staiggle against "ecological evil" (in our case, Mnemiopsis)can far from always bear expected fruit. If we speak about settling Beroe comb jelly in the Caspian Sea, then (from general considerations) the southern, warmer and more salty part of the basin seems to be more perspective.

ABOUT EFFICIENCY OF INTERGRATED STUDIES

- So, Russian scientists have found out the reasons and interrelations of many processes taking place in the Black Sea. This topic is also interesting for foreign researchers. How do the data obtained by you correlate?

- I believe that today the Russian Academy of Sciences is a leader in exploration of mechanisms of the Black Sea ecosystem operation. Thanks to 30-year integrated researches, the volume of our data and level of their comprehension are high and allow to soundly judge about development tendencies of the Black Sea. Foreign scientists have also stored precious data. However, one can dispute some of them.

Thus, several years ago the information about abnormal approach of hydrogen sulfide to the Black Sea surface was published in an international academic journal. However, the occasional stationary measurements upon which authors rest their conclusions cannot give an adequate idea of what is taking place. And the reason is simple: examining parameters of this ecosystem, it is necessary not only to "deal with" geographic coordinates but the dynamic ones which in this case depend on intra-basin circulation changing outlines of the upper bound of the notorious hydrogen sulphide layer. As we have mentioned, the depth of its bedding within the limits of the basin is not equal, it is the smallest in the center, and this "top" can move year in, year out. The first time foreign researchers didn't detect it, as it was in another area. However, when they came some time later, they found it hence their conclusions about the disastrous situation in the basin.

The tradition of Russian academic science to far and wide examine a natural object helps us avoid similar errors. We do not think it efficient to plan sea expeditionary works with a narrow range of problems. Often in order to adequately

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Influence of Beroe ovata upon seasonal dynamics of Mnemiopsis leidyi population. Dynamics of Mnemiopsis number: A - before settlement of Beroe, B - after its settlement and mass development in 1999.

understand the developments taking place in the ocean, one has to switch over from one kind of research to the others. This shall give a result which is often of key importance for discovering the essence of natural processes and of great practical importance. Unfortunately, this approach is not always applied. I shall give a typical example.

In 1997 - 1998, in the area of 0.5 mln km² of the Bering Sea one could see an outburst of abnormal flowering of coccolithophora - small (about 10 microns) algae with a calcic skeleton which normally are of little importance in the ecosystem. However, when their number reached 6 - 10 mln/1, transparency of water reduced 3 times, biological production significantly decreased. This phenomenon resulted in collapse of fishery: in the Bristol Bay they forecasted arrival of red fish in the number of 50 mln species, while a real figure proved to be 15 times smaller. Similar picture was observed in the Yukon River delta. By the way, recently, mass development of coccolithophora has been seen not only in the places of their traditional abundance but also in those regions of the World Ocean where they were present within the mark only in a small number, including the Black Sea. We don't know reasons as yet. The situation about which I started to speak related to the strongest global phenomenon El Nino.

Evidently, abnormal flowering is an extremely interesting phenomenon requiring an examination. At that time several American expeditions worked in the Bering Sea, and they crossed the abovementioned area many times. However, they neither made necessary measurements, nor selected sampling materials: this was not included in the planned program. If the expedition of our Institute were in their place, this would not have happened. By the way, the first information about the phenomenon of abnormal flowering of coccolithophora in the Bering Sea was published in the Russian journal Oceanology in 1998, as thanks to successful concurrence of circumstances we managed to take necessary sampling materials.

- The accumulation of various data is also an important problem. For these purposes the interested countries must carry out the coordinated ecological monitoring in the Black Sea.

- The duty of fundamental science is to provide a basis for monitoring which later observers of any qualification can carry out. To explain this thesis, let's appeal to the results of our multiyear researches.

In the Black Sea the shelf is rather narrow, its benthic biotic communities very much depend on transparency of water, the degree of its contamination. Before 1988 there was a steady developed ecosystem here: cistozir algae prevailed in the upper part, while red algae phyllophora - in the lower part (approximately up to the depth of 28 m). They formed the thickest "underwater forest" in which more than 120 species of the invertebrates dwelled, and it protected benthic community from invasion of predacious organism Rapana. However, Mnemiopsis settled in the basin and started eating zooplankton. Accordingly, pressing on phytoplankton reduced, while quantity of natural suspended matter increased. Moreover, comb jelly excretes a sea of mucus. As a result, transparency of water significantly reduced: in the open basin from 20 to 13 m, in shelf zone - from 20 to 5 m. What happened to benthic community? Phyllophora was lost, while the lower bound of underbrush cystozira found itself at 12 m and not 20. The reason is that benthic algae need light of a certain degree and range, while with roiling of water they can get no required lighting at all. As a result, the area of community habitats typical of the basin was reduced by approximately 60 percent.

With degradation of phytobenthos, zoobenthos lost protection and a considerable part of benthic typical community habitats and was practically destroyed by Rapana. Benthic community switched over to cyclic nature of existence: with sharp reduction in the quantity of food the number of Rapana decreases, while "peaceful" zoobenthos starts recovering, but when Rapana "lifts up its head", the rest of zoobenthos disappears. According to our information, the cycle lasts for 5 years. If only biologists studying individual types of organisms worked in the Russian expedition, we wouldn't have sorted out all mechanisms. With multidisciplinary researches including measurement of transparency of water, its spectral indexes, analysis of benthic sediments and suspended matter, the connection

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between phenomena and reason for them becomes apparent. An important difference of bio-oceanology from sea biology is here.

THE BASIS FOR INTERACTION WITH THE WORLD OCEAN IN THE 21ST CENTURY

- What are, in your opinion, prospects for domestic biooceanology development?

- Our science works for the man to be able to make correct forecasts of variability of sea and ocean ecosystems and understand how to manage them, how to minimize his influence on nature.

The building of wrongly designed constructions of coastal protection can serve as a concrete example of unskillful interference in ecosystem. It, by virtue of a whole complex of the processes in coastal zone, results in intensive erosion of the Black Sea beaches. Maintaining of the latter requires filling of beach material at strictly defined places, first of all, in river mouths, which will be spread along the coast by a system of streams. According to our estimates, to level off the most threatened Russian pebbled beaches, it is necessary to fill about 240 thous. m of material, while, in fact, it does not exceed 90 thous. m. The consequences of these "economic activities" are evident.

The more sad results can be obtained if the vector of man-made influence coincides with the climatic one. A well-known example is the situation with Peruvian anchovy at the beginning of the 1970s. At that time its catch amounted to 12 mln tons (to understand the level: modern catching of Alaska pollack in the Bering Sea, the largest in the world, amounts to 3.5 - 4 mln tons). Fishing area is a 12-mile strip at the coast, while income is colossal-more than 60 percent of currency receipts for the countries making a living by it. Specially processed fish flour from anchovy was used to produce concentration feed for agricultural animals, which defined a high international demand. The Peruvians and Chileans were obliged for their well-being to the phenomenon of coastal upwelling at which biogenic elements from the ocean deep layers come up to the surface, while the bright sun determines the most powerful growth of algae and phenomenal biological production which has no equal in the World Ocean. And anchovy, as a matter of fact, lives in natural cultivator.

However, in 1972, the strongest El Nino broke out - a phenomenon stopping the cultivator at the coast of South America. In such periods upwelling stops operating: it is covered by the Pacific waters as by a warm blanket, and productivity dramatically falls. Scientists strictly recommended to stop fishery during that time, but nobody listened to them, and after the highest catch, in the whole history of catch, of 12.4 mln tons in 1972, a complete collapse of fishery began in 1973: 300 thousand tons were caught, then fishing fleet stopped. The population of the Peruvian anchovy has not been restored till today.

Thus, scientific forecasts are extremely precious for practice because they are based on fundamental researches, and it is vitally important for Russia to preserve available scientific tools which have no equal in the world. As a matter of fact, this is our national heritage.

And more about prospects. Presently, we work mainly in internal seas but already today the development of global economic situation requires full study of the World Ocean under the bed of which, by existing estimates, there are 65 - 73 percent of hydrocarbon material-oil, gas, gas hydrates. Moreover, in future it will serve as the most important source of dietary protein. National scientific publications in priority international and Russian sources will play an important role in acknowledgement by the world community of the right of one or another country to extract these minerals and sea products. I believe that Russia can become a leader in the future researches of the World Ocean.

Provided materials have been obtained within the framework of the Federal target program "Exploration of the World Ocean Nature" and Program of Fundamental Researches of the RAS Presidium "The World Ocean".

Illustrations supplied by RAS Institute of Oceanology named after P. Shirshov