The Sea of Azov

Hdb Env Chem Vol. 5, Part (): 1–xDOI 10.1007/698_5_091© Springer-Verlag Berlin HeidelbergPublished online: September 2007

The Sea of Azov

Aleksey N. Kosarev1 · Andrey G. Kostianoy2 (�) · Tamara A. Shiganova2

1Geographic Department, Lomonosov Moscow State University, Vorobievy Gory,119992 Moscow, Russia

2P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, 36 NakhimovskyPr., 117997 Moscow, [email protected]

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Physico-Geographical Conditions . . . . . . . . . . . . . . . . . . . . . . 3

3 Ice Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4 Thermohaline Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Hydrochemical Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146.1 Phytoplankton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156.2 Zooplankton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166.3 Zoobenthos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166.4 Ichthyofauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

7 Introduced Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197.1 Phytoplankton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207.2 Zooplankton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217.3 Benthos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227.4 fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Abstract Based on the data of long-term observations, principal hydrological and hydro-chemical characteristics of the Sea of Azov such as the water temperature, salinity, andoxygen and nutrient contents are assessed. Features of the seasonal and interannual vari-ations under the action of natural and anthropogenic factors are shown. The biodiversityof the sea and the influence of the invader species on the state of the sea ecosystem areanalyzed in detail.

Keywords Sea of Azov · Kerch Strait · Physico-geographical conditions · Watertemperature · Water salinity · Oxygen content · Nutrients · Biodiversity · Invaders TSa

2 A.N. Kosarev et al.

1Introduction

The first First studies of the oceanographic and biological features of theSea of Azov started in the middle of the nineteenth 19th century [1]. Regu-lar surveying of the hydrologic and meteorological regime of the sea beganwith the development of a network of coastal hydrometeorological stations,as well as with sea expeditions on board of research vessels conducted at theend of the nineteenth 19th and at the beginning of the twentieth century by20th century by F. Wrangel (1873), I. Shpindler (1890), L. Antonov (1913), andothers [2–4]. From 1922 to 1928, In 1922–1928, N. Knipovich headed sea ex-peditions to the Sea of Azov and the Black Sea with the aim of oceanographicand fishery research [5–7]. From 1928 to 1932In 1928–1932, sea expeditionswere continued by a special fishery station, which was later reorganized intothe Azov and Black Sea Fisheries Research Institute (AzCherNIRO). In 1936,the USSR State Hydrometeorological Service set up a network of hydrome-teorological stations and standard hydrographic sections in the Sea of Azov;later, it was used by the State Oceanographic Institute (SOI) for the studiesof the hydrographic regime and regional climate. After World War IIWWII,the AzCherNIRO restarted research activities in the Sea of Azov. The results ofsea expeditions have been regularly published in Marine Hydrometeorologi-cal Yearbooks. Since 1952 the Azov Institute for Fishery (AzNIIRKH) has beencarrying out comprehensive research of hydrological, chemical, biological pa-rameters and fishery in the sea.

In the late 1980s, more than 20 coastal hydrometeorological stations wereproviding daily hydrographic and meteorological information. Six standardhydrographic sections across the Sea of Azov were used to collect physical,chemical, and biological data. This set of data was used for the descriptionof the state of the sea, its seasonal and interannual variability, as well as forthe assessment of biological resources [8–10]. Since 1997, Murmansk MarineBiological Institute (MMBI) and its Azov Branch (since 1999) have conductedmore than 40 scientific expeditions in the Sea of Azov [11–16]. The SouthernScientific Center of the Russian Academy of Sciences established in Rostov-on-Don in 2002, made a decision to rescue the historical oceanographic dataand to make them available to the international scientific community in orderto stimulate studies of the Sea of Azov. In 2006, this resulted in the NOAApublication Climatic Atlas of the Sea of Azov 2006, edited by Matishov andedited by G. Matishov and S. Levitus [17]. This atlas Atlas and the accom-panying CD-ROM contains oceanographic data collected by specialists of theUSSR and Russian Academy of Sciences, Ministry of Fisheries, and the Hy-drometeorological Service of the USSR and Russia in the Sea of Azov and theadjacent part of the Black Sea from 1913 to 2004. The atlas during 1913–2004.The Atlas contains monthly climatic maps of temperature and salinity at the

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The Sea of Azov 3

sea surface and depth levels of 5 and 10 meters. The interannual variability oftemperature and salinity of the Sea of Azov is also discussed.

The interest to the Sea of Azov was always related to its large fish stocks,which are inferior only to that of the Caspian Sea. Annual fish hauls (stur-geons, pike-perchspikeperchs, breams, and sea roaches) in this small seareached 300 kt. This triumph of fishery was confined to the period of the nat-ural harmony between the processes in the sea, when it was characterized bya high quality of the environment.

Previous to the early 1950s, under the natural water regime, the Sea ofAzov was distinguished by its extremely high biological productivity. Theriverine runoff delivered great amounts of nutrients, 70–80% of which weresupplied during the spring flood period. This provided abundant develop-ment of phytoplankton, zooplankton, and benthos. The area of the spawningzones related to flooded regions and lagoons in the lower reaches of the Donand Kuban’ rivers reached 40 000–50 000 km2. Along with the good heating,low salinity, sufficient saturation with oxygen, long vegetation period, andrapid cycling of nutrients, these factors provided conditions favorable forichthyofauna that included up to 80 species [18].

Today, the basin of the Sea of Azov represents a well-developed industrialand agricultural region. The formation of the industrial and agricultural com-plex in the basin of the Sea of Azov is related to the regulation of the riverinerunoff, to the partial use of the runoff, to the intensive industrial and civilconstruction, creation of irrigation systems in the sea watershed, and to thedevelopment of road–transport hubs, etc. This resulted in significant changesin the sea owing to the decrease in the volume of the freshwater supplied. Theecological changes resulted in a sharp drop in the biological productivity ofthe sea. The trophic base for fish fishes decreased by several times and thetotal hauls reduced, mostly at the expense of valuable fish species.

2Physico-Geographical Physico–Geographical Conditions

During its rich history, the Sea of Azov had many different names. AncientGreeks called it Maeotian Lagoon (Maeotian Lake), while Romans referred toit as Palus Meotis (Maeotian Marsh) after the tribe Maeotae that dwelled on itscoasts. In the antique Antique epoch, locals called it Temerinds. In medievalthe Medieval times, Russian name for it was the Surozh Sea after the name ofthe Crimean town of Surozh (now Sudak).

The Sea of Azov is the most shallow-water and one of the smallest seas ofthe world. Its area is 39 000 km2 at a volume of 290 km3; the average depthis 7 m with a maximum value of 14 m. It is connected with the Black Sea bythe a narrow (up to 4 km), and shallow-water (up to 15 m) Kerch Strait. The


maximum length of the sea is 360 km at a maximum width of 180 km. Thefirst sailing directions for the Sea of Azov (1854) were was compiled by sec-ond lieutenant A. Sukhomlin, who spent two years studying the coasts of thesea.

The sea features rather simple outlines. The northern coast is even andsteep with accumulative sandy spits. In the northeast, the largest of the seabays – Taganrog Bay – penetrates into the land; its top coincides with thedelta of the Don River. In the west, the Arabatskaya Strelka Spit separatesSivash Bay from the sea. The bay is connected with the sea by the GenicheskStrait. Sivash Bay (or the Gniloye Sea) represents a system of shallow-waterbays with a total area of 2560 km2. Their depths are 0.5–1.5 m, with at a max-imum value of 3 m. Annually, Sivash accepts up to 1.5 km3 of the water fromthe Sea of Azov. Owing to the strong evaporation, the Sivash water transformsinto saturated salt solution (brine, or rapa) with a salinity reaching 170 psu.Similar to Kara Bogaz Gol of the Caspian Sea, Sivash Bay provides variouschemical resources. It contains millions of tons of salt, magnesium sulfate,sodium sulfate, bromine, and other ingredients. For a long timelong, table saltworks existed in Sivash Bay. Mirabilite is also extracted from the Sivash brinesthrough salt precipitation.

In the southeast, the delta of the Kuban’ River with vast flooded plains andnumerous channels extends over about 100 km. The Kuban’ River enters thetop part of the open Temryuk Bay. Low seacoasts gradually descend to a flatsandy bottom. The depths smoothly increase with the distance from the coast.The largest depths are observed in the central part of the sea; in Taganrog Bay,they range from 2 to 9 m. In Temryuk Bay, mud volcanoes are known. Themain sources for the supply of the terrigenous matter that forms the bottomsediments of the Sea of Azov are represented by the products of coastal abra-sion and the riverine alluvium. The bottom sediments are mostly representedby clayey and silty oozes and sands.

Essentially, the Sea of Azov is a vast zone of mixing between the riverineand Black Sea waters. Almost the entire riverine runoff to the sea (more than90%) is provided by the Don and Kuban’ rivers and its major part is confinedto the spring–summer season. The principal exchange between the waters ofthe Sea of Azov and those of the Black Sea is implemented via the Kerch Strait.

The climate of the Sea of Azov, which deeply penetrates into land, is con-tinental. It is characterized by cold winters, and dry and hot summers. In theautumn–winter period, the weather is determined by the influence of a spurof the Siberian anticyclone with a domination of easterly and northeasterlywinds with a speed of 4–7 m/s. Enhancements of the impact of this spurcause strong winds (up to 15 m/s) and are accompanied by invasions of coldair masses. The mean monthly temperature in January ranges from – 1 to– 5 ◦C; during northeasterly storms, it may fall down to – 25 to – 27 ◦C.

In the spring–summer period, warm and fair fairy weather with weakwinds prevails. In July, the mean monthly temperature over the entire sea

The Sea of Azov 5

equals 23–25 ◦C, while its maximum values reach more than 30 ◦C. In thisseason, especially in the spring, Mediterranean cyclones often pass over thesea; they are accompanied by westerly and southwesterly winds with speedsof 4–6 m/s, and sometimes by gusts.

The water balance of the Sea of Azov consists of the following com-ponents: the incoming part contains the riverine runoff and the atmo-spheric precipitation, while the outgoing outcoming part includes evapo-ration. The water exchange via the Kerch Strait should also be taken intoaccount. According to the data averaged over 1923 to 19851923–1985, theriverine runoff, precipitation, and evaporation comprised 38.6, 15.5, and34.6 km3/year, respectively. The annual inflow of the Black Sea waters via theKerch Strait was 36–38 km3/year, while the outflow of the Azov waters com-prised 53–55 km3/year; this provided a value of the resulting water removalfrom the Sea of Azov of about 17 km3/year.

An analysis of the water balance of the Sea of Azov over the years citedshows that the components of the balance changed in the period of the reg-ulation of the riverine runoff in 1951. On average, the riverine runoff to thesea reduced by 5.7 km3/year, the supply of the Black Sea waters increased by1.5 km3/year, and the outflow of the waters of the Sea of Azov to the Black Seaincreased by 1.9 km3/year. Meanwhile; meanwhile, on the whole, the waterbalance remained almost the same.

The winds that dominate over the sea induce significant surge (onset) sealevel oscillations. The highest sea level rises were registered in Taganrog,where they reached 6 m. At other sites, rises ranging from 2 to 4 m withrange of are possible (Genichesk, Eisk, and Mariupol’); in the Kerch Strait,they reach a height of about 1 m. The limited sizes and small depths of the seafavor rapid development of wind waves. The waves are short and step; in theopen sea, they are up to 1–2 m, sometimes 3 m high.

Sharp changes in the atmospheric pressure and winds over the Sea of Azovmay also induce seiches – freestanding oscillations of the sea level. In the portareas, seiches with periods from a few minutes to a few hours are generated.In the open sea, seiches with a diurnal period up to 20–50 cm high are noted.

Seasonal changes in the sea level mainly depend on the regime of the river-ine runoff. The annual sea level change is characterized by its rise in thespring–summer months and a fall in the autumn and winter with averagetotal range of 20 cm.

The currents in the sea are mostly induced by the wind. Under the forc-ing by westerly and southwesterly winds, an anticlockwise water circulationin the sea is formed. The cyclonic water movement is also characteristic undereasterly and northeasterly winds as well when they are stronger in the easternpart of the sea. If these winds are stronger in the southern part of the totalabundance, the circulation has an anticyclonic character. At weak winds andcalm, insignificant currents current of intermittent directions are observed.Since weak and moderate winds dominate above the sea surface, currents


with velocities lower than 10 cm/s feature the highest recurrence rates. Understrong winds up to 15–20 m/s, current velocities increase up to 60–70 cm/s.

In Taganrog Bay, the resulting water transport is controlled by the runoff ofthe Don River and is directed from the bay toward the sea. In the Kerch Strait,under northerly winds, the current flows from the Sea of Azov to the BlackSea; winds with a southerly component provide the supply of the Black Seawaters to the Sea of Azov. The dominating current velocities in the strait growfrom average values of 10–20 cm/s to 30–40 cm/s in its narrowest part. Afterstrong winds, compensatory currents current are generated in the strait.

3Ice Conditions

In the Sea of Azov, ice is formed every year; in so doing, the ice coverage (seaarea covered with ice) strongly depends on the character of the winter (severe,moderate, or mild). In moderate winters, ice is formed in Taganrog Bay by thebeginning of December. During December, fast ice is formed along the north-ern coast of the sea and somewhat later along its other coasts. The width of

Fig. 1 Ice in the Sea of Azov revealed from a MODIS-Aqua satellite image on March 10,2006. Image courtesy of D.M. Soloviev, Marine Hydrophysical Institute, Sevastopol,Ukraine

The Sea of Azov 7

the fast ice band ranges from 1.5 km in the south to 6–7 km in the north. Inthe central part of the sea, floating ice is formed only at the end of Januaryor the beginning of February; subsequently, it freezes together and forms icefields with high ice concentration numbers (9–10). The ice cover is most de-veloped at the beginning of February, when its thickness reaches 30–40 cm(60–80 cm in Taganrog Bay).

Throughout the winter, the ice conditions feature instability. The mutualreplacements of the cold and warm air masses and wind fields over the seacaused repeated breaking and drifting of ice fields and their hummocking. Inthe open sea, the heights of hummocks never exceeds 1 m, while off the Ara-batskaya Spit, hummocks may reach a height of 5 m. As a rule, during mildwinters, the central part of the sea is free from ice; it may be observed only inbays and lagoons along the coasts.

In mild winters, the release from ice occurs during March first in the south-ern regions and in river mouths, then in the north, and, finally, in TaganrogBay (Fig. 1). The average duration of the ice period is 4.5 months. In anoma-lously warm or severe winters, the times of ice formation and thawing may beshifted by 1–2 months or even greater.

4Thermohaline Structure

Due to the small sizes and small water depths of the sea, the principal char-acteristics of the hydrological and hydrochemical regime are subjected tosignificant natural and anthropogenic variations.

In the shallow-water Sea of Azov seasonal changes in the water tempera-ture are very strongly manifested. In the winter (January to FebruaryJanuary–February), over the greater part of the sea area, the sea surface temperatureequals 0–1 ◦C; only in the region of the Kerch Strait, it grows up to 2–3 ◦C.In the summer (July to AugustJuly–August), the temperature is homogeneousover the entire sea area being equal to 24–25 ◦C (Fig. 2). The maximum valuesin the open sea reach 28 ◦C, while near the coasts they may exceed 30 ◦C.In the near-bottom layer of the sea, the temperature distribution is generallyclose to the values registered at the surface of the basin.

The shallow-water character of the sea provides rapid propagation of windand convective mixing down to the bottom, which leads to equalizing the ver-tical temperature distribution; in most cases, the temperature difference isless than 1 ◦C. Meanwhile, during summertime calm periods, the thermoclineis formed which that prevents the near-bottom layer from water exchange.

Under the conditions of natural riverine runoff, the salinity distribution inthe sea was rather homogeneous; horizontal gradients were observed only inTaganrog Bay, at the exit from which, salinity values of 6–8 psu dominated


Fig. 2 Mean multiannual water temperature (◦C) in the Sea of Azov at a level of 0 m ina February and b August [17]

(Fig. 3). This bay is filled with desalinated waters with a salinity of about2–7 psu. In the open sea the salinity ranged from 10 to 12 psu; in almost al-most in all of the regions, gradients were episodically observed and they weremainly related to the supply of the Black Sea waters. The seasonal salinitychanges never exceeded 1 psu; only in Taganrog Bay, where they enhancedunder the influence of the intraannual runoff distribution. Most frequently,high vertical salinity gradients are formed in Temryuk Bay, where the watersof the Kuban’ River are delivered to a relatively deep-water near-mouth sea

The Sea of Azov 9

Fig. 3 Mean multiannual water salinity (psu) in the Sea of Azov at a level of 0 m ina February and b August [17]

area. In the spring of 1980, the salinity difference between the surface and thebottom here reached 9 psu.

The multiannual changes in the salinity of the Sea of Azov are closely re-lated to the variability in the overall humidity in its watershed. For example,during the stage of enhanced humidity in 1924–1932, the average salinity ofthe sea has decreased from 10.5 to 9.6 psu. During the period of reducedhumidity in 1947–1953, the salinity rose rised from 10.7 to 12.7 psu. The reg-ulation of the Don River runoff in 1952 and the one-time removal of about


Fig. 4 Long-term (1922–1989) changes in the average salinity of the Sea of Azov (psu)

25 km3 of the Don River waters in order to fill in the Tsimlyansk Reservoirprovided the rapid growth of the salinity of the Sea of Azov (Fig. 4).

In 1953–1955, the average salinity in the sea reached 12.6–12.7 psu. A Thegrowth that great was caused not only by the irreversible withdrawal of therunoff but also by the fact that it was preceded by a depressive phase of thetotal humidity of the sea basin with a maximum at the beginning of the 1950s.Later (starting from 1956), the humidity in the basin of the Sea of Azov in-creased again; this phase of the climatic condition has lasted until 1968 andfavored the stabilization of the salinity at a level of 11.3–11.7 psu.

The dynamics of the mean annual salinity of the Sea of Azov (by the ex-ample of 1952–1968) shows that, even active irreversible withdrawal of thewaters, climatic factors may make a significant favorable effect on the resultsof the anthropogenic activity in the sea basin. On the contrary, the decreasein the total humidity in the basin after 1968 amplified the aftereffects of theirreversible runoff withdrawals when, in 1973, the Kuban’ River was regulatedand the Krasnodar Reservoir was filled. In the 1970s, the integrated annualriverine runoff to the Sea of Azov was 22–27 km3/year, a value more thanwhich value is more than by 40% lower than the natural norm. As a result, thetendency to increase an increase in the salinity of the sea was enhanced. Thestrongest salination was observed in 1975–1977, when the salinity in the seacomprised 13.3–13.9 psu, while in Taganrog Bay it was 9.5–11.1 psu.

On the whole, as a result of the coupled effect of climatic and anthro-pogenic impacts, the salinity maximum in the Sea of Azov in 1975–1977exceeded the natural norm by more than 3.0 psu and, in Taganrog Bay, evenmore. Beginning from 1978, the regime of the sea reached its new water-rich

The Sea of Azov 11

phase, the mean annual salinity of the sea acquired a tendency to fall, and, in1980s, it comprised 11–12 psu. By 2000 salinity lowered even to 10–11 psu.

In 1950–1970, the increased withdrawals of freshwaters for municipal pur-poses resulted in a decrease in the riverine runoff to the sea and a correspond-ing increase in the delivery of the Black Sea waters. The spatial inhomogene-ity of the salinity became noticeable; in the near-Kerch region, especially inlow-water years, its values grew up to 15–18 psu, i.e., up to values that havenever been observed from the beginning of the century.

At present, the Sea of Azov is characterized by the existence of salinityfrontal zones in the regions of the riverine water transformation in the near-mouth areas of the Don and Kuban’ rivers and in the zone of mixing betweenthe waters of the Sea of Azov and the Black Sea. The salt exchange with SivashBay is insignificant and its influence involves only a small region near theTonkii Strait. The central part of the sea is occupied by a homogeneous watermass with a salinity of 11–12 psu (see Fig. 3).

The enhancement of the propagation of the Black Sea waters in the near-bottom layers resulted in a growth in the vertical salinity and density gra-dients and deterioration of the conditions of mixing and ventilation of thenear-bottom waters. Also increased the probability of the formation of theoxygen deficiency (hypoxy) and conditions lethal for hydrobionts.

In accordance with the distributions of the water temperature and salinity,the vertical density gradients reach their maximal values in frontal regions –Taganrog Bay and the near-mouth area of the Kuban’ River, and in the near-Kerch region.

The regulation of the riverine runoff, its reduction by 13–15 km3/year,the creation of reservoirs, and other aftereffects of the anthropogenic activityin the basin caused serious negative changes in the sea ecosystem. The 30%drop in the annual runoff of the Don River and the significant decrease in theflooding volumes resulted in the reduction of the spawning areas and violatedthe conditions of reproduction of freshwater fish species [10, 18].

5Hydrochemical Conditions

The oxygen regime of the Sea of Azov is mainly rather favorable; water satu-ration with oxygen is sufficient and oxygen distributions over area and depthare rather uniform. According to the generalized data of multiyear observa-tions, in the winter, the average absolute oxygen content in the surface layer is330–370 µM in the open sea and 420–470 µM in Taganrog Bay. In the spring,the oxygen content equals contents equal 360–380 µM both in the open seaand in Taganrog Bay and the water is well aerated from the surface to thebottom (the relative oxygen content is about 100% or even slightly higher).


In the summertime, when the water temperature grows, the absolute oxygencontent decreases. In the open sea, its average value in the warm season isabout 260 µM (100%) in the surface layer and 200 µM (about 80%) in thenear-bottom layer. In Taganrog Bay, the oxygen contents in respective layersequal 270 µM (100%) and 220 µM (85%). Meanwhile, in the central part ofthe sea, the oxygen content in the near-bottom layer may locally drop downto 110 µM. In the autumn, the water temperature fall causes cause a uni-form oxygen distribution: 280–290 µM in the Sea of Azov and 230–310 µM(90–95%) in Taganrog Bay.

In the summer, the weakening in the vertical mixing in the sea resultsin the formation of oxygen-deficient zones in the near-bottom layers. Theseconditions lead to the appearance of suffocation zones often accompaniedby extinction of bottom fauna. The principal reasons for the summertimeoxygen deficiency are related to the high contents of the easily mineralizableeasily-mineralizable organic matter in the water and bottom sediments, theenhancement of the vertical temperature stratification owing to the sea heat-ing, and the salinity gradient increase caused by the changes in the riverinerunoff. The frequency of the formation of oxygen-deficient zones as well astheir area areas and intensity are closely related to the general character ofthe hydrological conditions in the sea (wind activity, salinity regime, amountand composition of the nutrients supplied to the sea, etc.). Therefore, thesummertime near-bottom oxygen deficiency in the Sea of Azov is subjectedto a significant interannual variability. This phenomenon was long known inthe Sea of Azov; however, it was observed only episodically. In the 1960s and1970s1960s–1970s, an active development of the reduction processes in thenear-bottom layer occurred related to the beginning of the process of anthro-pogenic salination of the sea accompanied by a weakening of the wind activityover its area. In July 1987, the presence of hydrogen sulphide was registeredin the Sea of Azov for the first time in history; its content in Temryuk Bay was20–35 µM.

The significant anthropogenic impact that suffers the Sea of Azov suffers ismanifested in the delivery of great amounts of organic matter and nutrients aswell as of technogenous pollutants. Under these conditions, the dwelling en-vironment of young sturgeon fish was fishes reduced to the area of TaganrogBay (about 12% of the total sea area). From In 1989–1990, the presence of hy-drogen sulphide was detected in the central part of the sea and in Berdyanskand Temryuk bays.

The present-day hydrochemical conditions in the Sea of Azov, includ-ing the distribution of nutrients, are described using the materials of thecruise of R/V Akvanavt that was carried out in July to August July–August2001 [19]. According to the data of observations, the Sea of Azov featuresa two-layered structure. In so doing, the upper layer, 7–10 m thick, consistedof three water masses. The waters of the Black Sea origin with a salinity higherthan 11.5 psu, oxygen content of 170–190 µM (less than 85% of saturation),

The Sea of Azov 13

phosphate content of 0.7–0.9 µM, silicate content of 8–12 µM, nitrate con-tent of 0.4–0.6 µM, nitrite content of 0.05–0.1 µM, and ammonium contentof 1.0–2.0 µM, occupied the eastern part of the sea. Fresher waters of theriverine origin with a salinity lower than 10 psu were supplied from Tagan-rog Bay and propagated in the form of a tongue extended along the northerncoast of the sea. They were characterized by enhanced contents of oxygen(250–300 µM, or more than 120% of saturation), silicate (28–32 µM), andnitrites (0.15–0.25 µM), by an insignificant growth in phosphate contents(1.0–1.3 µM), and by a decrease in the contents of nitrate (0.3–0.5 µM) andammonium (lower than 1 µM).

The surface water of the central and western parts of the sea was charac-terized by intermediate values of these parameters. Over the entire sea area,the concentrations of the main forms of nutrients were sufficiently high anddid not didn’t restrict the phytoplankton development, which points to thesignificant trophicity of the sea.

Among the most interesting results of the cruise was that suffocation zoneswere found one finds the suffocation zones no thicker than 1.5 m with highhydrogen sulphide contents revealed in the near-bottom layer. The anoxiclayer was separated from the overlying layers by a pycnocline 0.5–1.5 m thick.The high density gradients prevented the layers of the sea from the verticalwater exchange. The near-bottom layer was characterized by an increase inthe contents of hydrogen sulphide (80–90 µM), ammonium, and phosphates.In the Sea of Azov, the concentrations of all the reduced compounds nearthe boundary of the hydrogen sulphide layer corresponded corresponding tothose in the Black Sea at depths 50–100 m below this boundary. This suggestsa higher intensity of the processes of mineralization of organic matter anda stability of the stratification in the waters of the Sea of Azov.

The principal reason for the formation of anoxic conditions in the Sea ofAzov (as well as in other inland seas) lies in the imbalance misbalance be-tween the organic matter supply and the income of dissolved oxygen requiredfor its oxidation. In the formation of the suffocation conditions in the Sea ofAzov, certain roles belong both to the allochtonous organic matter deliveredwith the riverine runoff and to the autochtonous matter generated in the seaproper. The supply of nutrients is implemented with the runoff of the Donand Kuban’ rivers and via the Kerch Strait, while their removal is related to theoutflow to the Black Sea, extraction in the course of fishery activity, and bury-ing in the bottom sediments. The results obtained in the cruise are evidenceof bring evidence on the strong eutrophication of the entire area of the Sea ofAzov and of on its critical ecological state.

A characteristic trend in the present-day nutrient dynamics in the wa-ters of the rivers of the Sea of Azov basin lies in the decrease in the contentof phosphorus (Ptot) and the increase in the nitrogen content. After regula-tion of the runoff, the internal structure of the nutrient runoff – nutrient tophosphorus concentration ratio – has been sharply distorted. Under the nat-


ural conditions, the values of the N/P ratio were 3.9 and 4.5 for the Don andKuban’ rivers, respectively, and later they became 17.6 and 11.5, respectively.The differently directed trend of the changes in the nitrogen and phosphoruscontents in the riverine waters of the Sea of Azov basin are related to the factthat , in the Tsimlyansk and Krasnodar reservoirs, accumulation of particu-late mineral and organism phosphorus takes placeproceeds. In the Don Riverwaters, a strong growth in the nitrogen concentration occurred. Balance esti-mates for nitrogen and phosphorus in the Sea of Azov showed that the mostvariable component of the balance is related to the burying of nutrients in thebottom sediments.

It seems impossible to calculate an exact nutrient balance for the Sea ofAzov. According to the estimates available for the period from 1952 to 1976,the input/output values are evaluated in the ranges 75–122 and 8–17 kt for thetotal nitrogen and for the total phosphorus, respectively.

The hydroeconomic situation in the Sea of Azov basin is very tense. Atpresent, about 30–40 km3 of riverine waters are annually supplied to the sea.Under this runoff intensity, there is a possibility of retaining the seawatersalinity in the range up to 11–12 psu. The further growth in the water con-sumption is prohibitive since it should cause a salinity growth up to the BlackSea values thus deteriorating the dwelling conditions for most valuable ma-rine organisms.

6Biodiversity

After the Caspian Sea, the Sea of Azov is the second most significant inlandbasin of the USSR with respect to its fish stocks. Recently, every hectare of itsarea provided 80 kg of fishfishes, half of which was represented by valuableand very valuable species (sturgeons, pike-perchespikeperches, breams, searoaches, and others). The annual fish production in this smallest sea reached300 kt. This triumph of the Sea of Azov fishery was related to the times ofcomplete harmony between the natural processes, when the sea was charac-terized by a high quality of the dwelling environment.

This harmony was provided by three principal factors:

• The the sufficient delivery of riverine waters rich in nutrients to the seaand the high rate of their cycling. ;

• The the low salinity of the waters of the sea. ;• The the high provision of the reproduction of fish stocks: for migra-

tory and semi migratory species alone, the total spawning area exceeded600 000 hectares, while the habitat of marine fish fishes covered the entiresea area.

The Sea of Azov 15

The positive effect of the interaction between these factors was enhancedowing to the shallow-water character of the sea and its geographical position.Since the middle of the last century the environmental state of the Sea of Azovhas been is under great anthropogenic pressure, resulting . This results innegative changes in the sea biota.

6.1Phytoplankton

In the Sea of Azov and Taganrog Bay, based on multiyear studies of phyto-plankton, 605 species, varieties, and forms of purely or optional planktonicalgae were CE

b discoveredrevealed. With respect to the species number, di-atoms and green algae dominate. Blue-green algae and pyrophytes also fea-ture a high species diversity; euglene and yellow-green algae comprise about5% of the total species number [20].

The principal alga representatives in the Sea of Azov are planktonic algae.The low water transparency suppresses the development of bottom plants. Es-sentially, the production formed by phytoplankton serves as a source for lifeof the entire heterotrophic population of the Sea of Azov. Owing to the par-ticular features of the hydrological regime, the phytoplankton of the sea hascertain special features that are mostly typical of lagoons. The shallow-watercharacter of the sea and its good response to heating allow the algae to inhabitalmost the entire water column. The quantitative development and speciescomposition of phytoplankton in the open part of the sea are almost similarto those in the near-shore zone. The Sea of Azov is characterized by intensiveand rather long-term “blooming” periods, high concentrations of particulateorganic matter in the water, and frequent events of oxygen deficiency. Mean-while, with respect to the salt composition, to the relations between the totalsalt content and chlorinity, to the domination of pyrophytes and diatoma-ceous algae (marine species) in the sea, the Sea of Azov water is close to theoceanic water.

The great volumes of fresh and Black Sea waters delivered to the Sea ofAzov supply assemblages of algae and animals dwelling in these basins. How-ever, the extremely variable salinity of the seawaters makes possible dwellingand developing possible for euryhaline species only. The in it only of eury-haline species . Precisely the tolerance of algae to salinity changes preciselydefines the boundaries of their distribution in the Sea of Azov and TaganrogBay.

The region of the Sea of Azov proper with an average salinity of 11–12 psuis mostly inhabited by three ecological alga assemblages: the marine,brackish-water–marine, and brackish-water assemblages. The flora of Tagan-rog Bay, whose salinity varies from 3–4 to 9–10 psu, usually consisted ofspecies of the freshwater–brackish-water assemblage from the groups of blue-green, green, and diatomaceous algae [20].

CEb Please check my changes.



The increase in the salinity of the sea caused essential changes in the struc-ture of phytoplankton assemblages. Significant changes were also noted in thephytoplankton productivity, which is clearly manifested in the distribution ofphytoplankton and in the general a decrease in its biomass [20].

6.2Zooplankton

The planktonic fauna of the Sea of Azov consists CEb of representatives of

different originsof the representatives different in their origin. Species of thefreshwater, relic brackish-water, Pontian–Caspian, and marine assemblagesare encountered [21].

Each of the components inhabits this or that zone of the sea depending onits dwelling and reproduction range and features the highest density underthe conditions of its optimal salinity.

The eastern part of Taganrog Bay, where the salinity changes within therange of 0.5–4 psu, is inhabited by the freshwater and brackish-water Clado-cera and Copepoda. Rotifers are represented by mass amounts of the armoredrotifers Brachionus plicatilus, Keratella curdata, Asplanchna, which dwell infresh and brackish waters.

In the central part of the bay, the salinity changes within the limits 3–7 psu.Here, the composition of plankton features a mixed character. Along withbrackish-water and freshwater forms, marine forms are also encountered.

In the western part of the bay, that which directly faces directly face theopen sea, marine fauna are almost completely represented by is most com-pletely represented in plankton; it contains all the three forms of Acartiaclausi (the Azov, the small Black Sea, and the large Black Sea forms), Cen-tropages ponticus, meroplankton, larvae of the balanus B. improvisus, andlarvae of Gastropoda, Bivalvia, and Polychaeta.

The salinity variations in Taganrog Bay cause migration of the assem-blages. For example, under salination, the marine assemblage penetrates pen-etrated into the eastern assemblage domain, while at desalination, brackish-water and even freshwater assemblages penetrate into the western part of thebay.

In the Sea of Azov proper, zooplankton are is represented by a small num-ber of marine species mostly consisting of copepods. The dominating formsare A. clausi (the Azov, the small Black Sea, and, sometimes, the large BlackSea forms), C. ponticus, meroplankton, etc., as well as the rotifers of the Syn-chaeta genus. Earlier, small amounts of A. latisetosa were encountered.

In the periods of salination of the Sea of Azov, the invasion of a group ofplanktonic species from the Black Sea occurred [22].

The Sea of Azov 17

6.3Zoobenthos

The bottom biocoenoses of the Sea of Azov are characterized by low speciesdiversity and a rather high level of domination [23]. The principal compo-nents of the bottom fauna are represented by worms, crustaceans, bottomprotists, coelenterates, and mollusks. The latter comprise up to 60–98% of thetotal biomass of bottom invertebrates.

The structure and biomass of the biocoenoses change over a wide range,which that are defined by the combination of biotic and abiotic factors.Among the latter, most important are the salinity, the gas regime, and theproperties of the sediment. The biotic factors are the zoobenthos grazing byfish fishes and the competition for the dwelling environment between thebenthos representatives.

In Taganrog Taganog Bay, zoobenthos representatives referring to thefreshwater, relic brackish-water, and marine assemblages are observed. Beforethe runoff regulation, the Pontian–Caspian species Hypanis colorata, Dreis-sena polymorpha, and Hyraniola kowalevskyi densely inhabited the bay andsome of them distributed beyond its limits to the northeastern part of the Seaof Azov. The marine species Nereis succinea and Cerastoderma lamarcki wereencountered at the interface with the Sea of Azov and, partly, in the westernpart of the bay.

During the periods of salination, marine species widely inhabited the west-ern and central parts of the bay, while the Pontian–Caspian species wereencountered only in more desalinated regions [23].

6.4Ichthyofauna

In the Sea of Azov proper (including Taganrog Bay) and in the northeast-ern part of the Black Sea, ichthyofauna are comprised of contains 183 speciesand subspecies of fish fishes referring to 112 genera, 55 families, and 22 divi-sions. Of them, 50 species may be regarded as rare, 19 species are vulnerableand subjected to the hazard of disappearance, and the sturgeon Acipensernudiventris has most probably become extinct. In all, 39 marine species,8 freshwater species, 14 species of anadromous and catadromous migrants,and 42 species of inhabitants of brackish-water regions were registered [24](Fig. 5).

In 1975–1977, when the salinity in the Sea of Azov was extremely high (inparticular, in its southern part, values up to 15 psu were often noted), thisregion was visited, in addition to usual seasonal invaders (the anchovy En-graulis encrasicolus maeoticus, E. encrasicholus ponticus, the garfish Belonebelone euxiniBelone belone euxini, the mullet Liza (Mugil) cephalus, L.(M.)auratus, L.(M.) saliens, the friar Atherina mochon pontica, the whiting Mer-


Fig. 5 Commercial species of the Sea of Azov. 1 Sprat Clupeonella delicatula. 2 AzovSea anchovy Engraulis encrasicolus maeoticus. 3 TurbotScophtalmus maeoticus torosus.4 Sturgeon Acipenser guldenstadti

The Sea of Azov 19

langus merlangus euxinus, the pickarel Spicara smaris, and others), by thespecies that were extremely rare or those that have never been reported in theSea of Azov. The first group consists of the bluefish Pomatomus saltatrix, theBlack Sea plaices Scophathalmus rhombus and Psetta maxima maiotica, theblue stingray Dasyatis pastinaca, the spurdog Squalus acanthias, the kingfishkingfishes Sciaena umbra and Umbrina cirrosa, the Black Sea salmon Salmotrutta, the mackerel Scomber scombrus, the wrasse Crenilabrus ocelitus, theblenny Blenius zvonimiri, the blanket bullhead Aphya minuta, the sea smeltAtherina hepsetus, the thick pipe-fish Syngnathus variegatus, and others. Forthe first time in the Sea of Azov, the corkwing Crenilabrus griseus, the rockhoppers Blenius ponticus and B. sanquinolentus, the bullheads Pomatoschis-tus minutus and Gobius niger, the puntazzo Puntazzo puntazzo, and theMediterranean sea eelpout Gaidropsarus mediterraneus were encountered.Meanwhile, all the above-listed species (rare and first encountered) were metonly in small amounts mostly in the southern part of the sea. Only Gobiusniger, after penetration into a new basinbasin new for it, in two years becamea rather common fish not only in the southern areas but also in the north-ern regions (off Obitochnaya and Berdyansk spits) [25]. These facts suggestthat, in the years of salination of the waters of the Sea of Azov, its ichthyofaunamay be naturally supplemented by Black Sea immigrants that use to dwell inthe northeastern and northwestern parts of the Black Sea and can resist watertemperatures lower than 3–5 ◦C.

The fauna of Taganrog Bay is twice as poor as that of the Sea of Azovproper. It ; it includes 55 species referring to 36 genera and 16 families, and ; itmainly consists of freshwater and brackish-water forms and migrants. Among; among the latter, three species are rare and six species are vulnerable andsubjected to extinctionthe extinctionmenace [24].

The ichthyofauna of the lower reaches of the Don River, Kuban’ lagoons,and other basins of the region (in addition to the Sea of Azov and the BlackSea proper) including waterlogged areas, sea bays and lagoons is representedby 134 species and subspecies referring to 90 genera and 42 families; they arejoined into 17 divisions of three classes (one species of the lamprey Cepha-laspidomorphi, one species of the chondral Chondrichthys and 132 species ofthe bony fish fishes Osteichthyes) [24]. With respect to their ecology, 33.6% ofthe forms are freshwater, 26.1% are marine, 17.9% are brackish-water, 10.4%are anadromous, and 0.7% are catadromous species. Most of the fish fishes(77%) dwell in the near-bottom layer, while the rest are pelagic species [24].


7Introduced Species

All the alien species entered the Sea of Azov from the Black Sea via the KerchStrait with currents or with ships. Selected species negatively affected theecosystem, while the others enrich its flora and fauna [22, 26, 27]. SelectedBlack Sea fish fishes make their seasonal migrations to the Sea of Azov forspawning and fatting. In the years with enhanced supply of the Black Seawaters, purely marine species of Mediterranean and Atlantic origins invadedthe Sea of Azov. Some of them spread over the entire sea and even featuredoutbursts of their abundance.

7.1Phytoplankton

Owing to the continuous water exchange, the Black Sea serves as a supplier ofphytoplankton species to the Sea of Azov. Among them, one finds Melosiramoniliformis (O.Mull), Ag. v. moniliformis, Cerataulina bergonii Perag.,Nitzschia seriata Cl., Coscinodiscus radiatus Ehr., Chaetoceros rigidus Ostf.,Ch. affinis Laud. v. affinis, Pseudosolenia fragilissima Bergon, and others.Meanwhile, the distance of their penetration and the intensity of their devel-opment are limited by the salinity of the waters of the Sea of Azov. Therefore,marine stenohaline species are encountered within a narrow band near theKerch Strait and represent temporary components of the phytoplankton com-munity of the sea, while the most euryhaline species extend over the entirearea of the Sea of Azov [20]. In the warm seasons, phytoplankton of the fresh-water assemblage from the Don and Kuban’ rivers and from the lagoons of theKuban’ seaside also penetrate penetrates to the Sea of Azov. These seasonalinvaders make the greatest contribution to the local species communities inthe desalinated regions of Taganrog Bay and in river deltas.

Among the phytoplankton species, the first real alien species is the diatomalga Pseudosolenia calcar–avis (= Rhizosolenia calcar–avis); in 1908–1920, itpenetrated into to the Black Sea and, in 1924, it invaded the Sea of Azov. Asearly as 1924 to 1928in 1924–1928, its abundance in the Sea of Azov reached2.4–4.5 million cells; a similar outburst was also registered in the 1950s. Atpresent, pseudosolenia also often dominate the phytoplankton communityof the Sea of Azov in warm seasons [20]. Pseudosolenia appears in phyto-plankton in April–March and develops throughout the entire summer; it iscapable of dwelling in the Sea of Azov at a salinity of 10.4–12.9 psu anda temperature of 5.6–26 ◦C. Because of its large sizesizes, pseudosolenia canhardly be consumed by fish or fishes or , the more so, by invertebrates, and,at its mass development, it replaces more valuable aboriginal phytoplank-ton species. Among other alien phytoplankton species one can mention two

The Sea of Azov 21

diatom species – Bacteriastrum hyalinum Laud. and B. delicatulum Shad –discovered by G.S. Gubina in the 1980s and episodically encountered in theSea of Azov. Three planktonic diatom species more alien for the Sea of Azovpenetrated in from the northwestern part of the Black Sea: Cerataulina pelag-ica (= C. bergoii), Chaetocerus socialis, and Ch. tortissimus. All of them aremass species and Cerataulina pelagica often dominates during the periods ofincreased salinity values in the Sea of Azov [20].

Of all the phytoplankton species introduced to the Sea of Azov, only Pseu-dosolenia calcar–avis may cause negative effects on the sea ecosystem duringits bloom.

7.2Zooplankton

In the period of salination of the Sea of Azov, selected plankton species en-tered it from the Black Sea. Some of them such as Penilia avirostris, Sagittasetosa, Paracalanus parvus, and Rhisosthoma pulmo dwelled only in the re-gions of the maximal influence of the Black Sea waters and did not didn’tpenetrate beyond the southern part of the Sea of Azov. Other species such asOithona nana, O. similis, Labidocera brunescens, and the medusa Aurelia au-rita actively developed and soon covered the entire area of the basin [22]. Inthe 1970s, a mass development of the Black Sea medusa Aurelia aurita in theSea of Azov was observed. At present, the appearance of these kinds of speciesmay take place only at intensive advection of the Black Sea waters and theymay be regarded only as temporary invaders.

At the beginning of the 2000s, a new species that came from the Black Sea– Acartia tonsa – was encountered. At ; at present, it is present in all the zoo-plankton samples collected in the warm season of the year both in the Sea ofAzov proper and in Taganrog Bay; thus, it has formed its own reproductivepopulation.

In August 1988, a new Black Sea invader – the ctenophore Mnemiopsis lei-dyi – appeared in the Sea of Azov; it was first encountered near the KerchStrait in the southern and eastern parts of the sea. From that time, everyspring or summer, mnemiopsis has penetrated into to the Sea of Azov fromthe Black Sea with currents to provide an outburst in its development in thesummer or early autumn. Then; then, it became extinct at the temperaturedrop below 4 ◦C at the end of October to NovemberOctober–November [28].Mnemiopsis negatively affected the ecosystem of the Sea of Azov and under-mined its fish stocks.

The other ctenophore Beroe ovata, which spontaneously appeared inthe Black Sea in 1997, invaded the Sea of Azov in September to OctoberSeptember–October 1999 [29, 30] during its first bloom in the Black Sea [30].The penetration of Beroe ovata into the Sea of Azov and its migration areidentical to those of mnemiopsis: it appears in the southern part of the sea


and then expands over other areas. The main prerequisites that control theformation of the habitat of beroe, as well as in the case of mnemiopsis, are theintensity of the Black Sea water advection, the character of the winds, and theberoe abundance in the prestrait pre-strait area of the Black Sea. The beroepopulation ends eliminates at the onset of low seawater temperatures.

7.3Benthos

Among the representatives of benthos, the first alien species in the Sea ofAzov was Balanus improvisus, which appeared in the Black Sea as early as thenineteenth in the 19th century. At present, this is a typical representative ofthe benthos of the Sea of Azov. Its maximal biomass registered in the near-shore waters of Taganrog Bay equals 7 kg/m2 [31]. Being a fouling species,balanus causes damage to the ecology; meanwhile, its mass larvae serve asa food base for planktivorous fishfishes. In addition, empty valves of balanusprovide shelter for 18 bottom invertebrate species; some of them such as theamphipods Gammarus locusta, Stenothoe monoculoides, and Jassa ocia re-produce inside the valves [32]. Balanuses participate in the cleaning of theenvironment as filtrators.

In 1956, the rapana Rapana venosa entered the Sea of Azov from the BlackSea. It was encountered only in the southern regions of the Sea of Azov adja-cent to the Kerch Strait, where the salinity is the highest. The low salinity ofthe sea seems to prevent rapana from expanding a wide expansion over thebulk of its area.

Among bivalve mollusks, shipworms Teredo navalis, were the first encoun-tered; they invaded from the Black Sea in 1953–1955 during the increase inthe salinity of the Sea of Azov. Under low salinity values, their abundance islow, but when the salinity grows, in the warm seasons, outbursts of the massdevelopment of shipworms are possible; sometimes, they result in a rapiddamage or even destruction of wooden constructions. Among other bivalvemollusk species, in 1966–1967, the brackish-water species Mya arenaria wasencountered; it distributed over almost the entire Sea of Azov. At present, thisspecies represents an important component of benthos, mainly in the near-shore zone and, especially, in the regions with low oxygen contents, where thebiomass of mya in the biocoenosis varied from 110 to 1700 g/m2 [33].

In April 1989, one more species alien for the Black Sea, penetrated intothe Sea of Azov – Anadara inaequivalvis. A. inaequivalvis widely spread overthe Sea of Azov; it is regularly encountered in the Cerastoderma lamarkibiocoenoses and, under the decrease in the oxygen content, forms an inde-pendent biocoenosis in the near-bottom layers with a high biomass (up to600 g/m2) and a high species diversity (up to 30 species) over significant areasof the seafloor. At the present-day condition of the gas regime in the Sea ofAzov, the development of A. inaequivalvis as well as that of mya is a posi-

The Sea of Azov 23

tive phenomenon, because these mollusks populate biotopes with low oxygencontent contents not available for other species. Their assimilation providesan enhancement of the productivity through enrichment of the fodder basefor pelagic and benthivorous fishfishes. These species represent promising ob-jects for commercial use because they contain up to 40% of delicate meat [33].

The Black Sea mussel Mytilus galloprovincialis is one more bivalve molluskspecies that invaded the Sea of Azov at the end of the 1950s at the salinityincrease. Before the Don River runoff was regulated, only single mussel spe-cimens were encountered; later, when the salinity increased, mussels obtainedoptimal conditions for their development and it started to spread over the en-tire area of the basin [34]. PresentlyAt present, mussels also play an importantrole in the benthic biocoenoses of the Sea of Azov.

The Dutch crab Rhithropanopeus harrisi tridentata, which inhabited thebasin including Taganrog Bay in the 1960s, refers to the old invaders to the Seaof Azov; it is encountered even in the freshwater regions of the lower reachesof the Don River. This species dwells over sandy and clayey sediments in sea-grass thickets and serves as an additional food resource for benthivorous fishfishes such as bullheads, plaices, turbots, and sturgeons. Their invasion didnot didn’t hurt the ecosystem and was rather useful for it.

7.4fishFishes

The habitats of selected Black Sea fish fishes are adjacent to the Sea of Azov;however, usually, they were not encountered in it. For example, Taman’ Bayand the northern part of the Kerch Strait represent the northern boundaryfor 11 species and 36 species more permanently dwell in these areas (the re-gion near Feodosiya–Kerch–Novorossiisk). In the years of intensive advectionof the Black Sea waters to the Sea of Azov, these species may penetrate fartherreplenishing the fauna of the basin, especially off the Crimean coasts [24].In 1975–1976, in addition to the usual seasonal migrants (anchovy, garfish,mullets, friar, Black Sea whiting, pickerel, and others) species rarely encoun-tered here (bluefish, turbot, chuco, spurdog, Black Sea salmon, mackerel, andothers) penetrated into this region. For the first time in the Sea of Azov,corkwings, rock hoppers, bullheads, and eelpouts were observedrevealed.

Fig. 6 Mullet Liza haematochila (Mugil soiuy)


However, almost all of the above-listed species are mostly characteristic of thesouthern half of the sea and are observed in small amounts [25]. These factssuggest that the ichthyofauna of the Sea of Azov during the period of its salin-ity increase may be in a natural way significantly replenished by Black Seaimmigrants that use to dwell in the northeastern part of the Black Sea andare capable able of resisting water temperatures lower than 3–5 ◦C. There-fore, the ichthyofauna of the Sea of Azov is subjected to the similar processesof the temporary replenishment by Black Sea species, CE

b and may even betidal to may be even tidal a greater degree than in the case of the plant andinvertebrate communities.

In the Sea of Azov, measures for intentional introduction of commercialfish species from other basins have been taken. Among them, 15 introducedspecies (11%) originate from fresh and brackish waters of the Far East andNorth America. Most of the fish fishes introduced refer to the near-bottomspecies (77%), the rest (23%) are pelagic species [24]. However, the per-centage of the established species is low. The most successful intentionalintroduction action was the introduction of the mullet Liza haematochila(Mugil soiuy) (Fig. 6). The principal prerequisite for its introduction into theAzov–Black Sea basin was its high resistance to a wide range of salinity anddissolved oxygen changes. This fish is a typical detritofage and it was believedthat it would not compete with local fish species. In ; in addition, it had toutilize provide utilization of organic matter, whose amount strongly increasedafter the runoff regulation causing suffocation phenomena [35]. The condi-tions in the Sea of Azov were occurred very favorable for this mullet. It spreadover almost the entire area of the sea, in lagoons, channels, and river mouths.Every year, a part of the spawning population leaves the Sea of Azov for theBlack Sea. At present, the hauls of mullets are increasing. It has become be-came an important commercial fish both in the Black Sea and in the Sea ofAzov.

Among other intentionally introduced fish fishes introduced in line withthe development of the pond and lagoon–lake fish culture, one should notethree buffalo species, the motleys Aristichthys nobilis, the white Hypoph-thalmichthys molytrix (Valenciennes, 1844), the silver carps, and the whiteamur Ctenopharingodon idella. Silver carps and amurs spread in the lowerreaches of rivers and lagoons; now, they are commercial fish fishes of the Azovbasin [24]. The Caspian kilka Clupeonella cultriventris ñaspia, which is widelyspread in the Volga basin, penetrated also into to the lower and upper DonRiver and the reservoirs of the Manych system, and the Tsimlyansk Reservoir.

The Sea of Azov 25

8Conclusions

The regulation of the Don (1952) and Kuban’ rivers (1973) and the with-drawal of the riverine runoff for reservoir filling caused negative qualitativeand quantitative aftereffects in the runoff to the sea, in particular, reducedflooded and spawning areas. In the sea proper, one observes a growth in thevertical temperature and salinity gradients and an increase in the formationof oxygen-deficient zones in the near-bottom layer. In 1987, the presence ofhydrogen sulphide was first registered in the lower layers of the sea.

Under the present-day conditions, the amount and composition of thenutrients supplied to the sea radically changed as well as their distributionthroughout the year. The major part of the particulate matter precipitates inthe Tsimlyansk Reservoir, while its amount delivered to the sea in the springand at the beginning of the summer significantly decreased; simultaneously,the supply of mineral forms of phosphorus and nitrogen reduced, while theamounts of their organic forms that are hardly assimilated by organismssharply increased.

Meanwhile, the pollution of riverine and sea waters by different hazardouschemicals such as pesticides, phenols, and, at selected places, oil productsalso increased. The highest pollution degree is observed in the near-mouthregions of the Don and Kuban’ rivers and in the areas adjacent to major ports.These ecological changes resulted in a sharp drop in the biological productiv-ity of the sea. The trophic base for fish fishes multifold reduced and the totalfish hauls, especially those of valuable fish species, also decreased.

Summing Sum up the composition of alien species in the Sea of Azov, it isimportant to mention that the species which could establish themselves in thesea in the Sea belong to euryhaline, eurytherm, euryoxygen and stenobathno-shallow-water species. Total numbers of aliens comprised 46 species. Whenanalyzing the ecological role of species-invaders in the Sea of Azov, oneshould first mention the enormous negative effect at all the levels of itsecosystem, fish resources included, caused by the invasion of the predatorctenophore Mnemiopsis leidyi. The Pseudosolenia calcar–avis diatom alga, atits mass development, supplants more valuable aboriginal species of fodderphytoplankton.

The introduction of other organisms may be regarded as positive events.Benthic species such as mya and anadara widely spread over the regions withlow oxygen contents unfavorable for other benthos representatives; they pro-vided valuable food resources for benthofagous fishfishes, while their larvaeare consumed by small pelagic fishfishes. The role of the fouling species Bal-anus improvisus is negative; meanwhile, its larvae are consumed by smallpelagic fishfishes. The crab Rhithropanopeus harrisi tridentata also becamean additional food source for benthofagous fishobject for benthofagous fishes.


The ctenophore Beroe ovata is, beyond doubt, a useful invader; unfor-tunately, according to its seasonal dynamics, it appears in the Sea of Azovtoo late, when mnemiopsis has already reproduced, widely spread, and un-dermined the stocks of trophic zooplankton. No positive role of B. ovata inreducing the mnemiopsis population in the Sea of Azov was noted to date.Meanwhile, its development in the Black Sea influences the size of the mne-miopsis population; therefore, after the beroe appearance, mnemiopsis entersthe Sea of Azov later and its abundance is significantly lower.

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