The Europaen Commission The Commission on the Protection of the Black Sea Against Pollution
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Report Contents

Preface Chapter 1A Chapter 1B Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12
List of Tables List of Figures

State of Environment Report 2001 - 2006/7

Chief Editor, Prof. Dr. Temel Oguz, Institute of Marine Sciences, Middle East Technical University, Erdemli, Turkey

Chapter 12 - Overall Assessment of the Present State of the Black Sea Ecosystem

State of the Environment of the Black Sea - 2009

CHAPTER 12 OVERALL ASSESSMENT OF THE PRESENT STATE OF BLACK SEA ECOSYSTEM (T. Oguz et al.)

T. Oguz

Institute of Marine Sciences, Middle East Technical University, Erdemli, Turkey

V. Velikova1 and A. Kideys2

1Inebolu Sokak 29, Kabatas, Istanbul, Turkey

2 Bahcelievler Mahallesi, Aki Sokak, No 11, Uskudar, Istanbul, Turkey

12.1. Introduction

During the last three decades eutrophication has been identified as a key ecological problem for the coastal Black Sea regions and especially for its northwestern part where strong anthropogenic nutrient and pollution loads resulted in dramatic alterations in chemical and biological regimes. Eutrophication refers to undesirable disturbances in ecosystem functioning due to anthropogenic enrichment by nutrients and subsequent accelerated growth of algae and higher life forms. Rapidly intensifying eutrophication in the 1970s and 1980s transformed the formally diverse ecosystem with a rich variety of marine life into a degraded system with marked changes in composition and abundance at species level, and species communities and their interactions at the ecosystem level. A schematic of the transformations in the ecosystem level is depicted in Fig. 12.1.

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Fig. 12.1. Schematic representation of the Black Sea pelagic and benthic ecosystem transformations along the Black Sea western coast (after Friedrich et al., 2006).

In addition to eutrophication, other high priority transboundary ecological problems are the decline in living resources (mostly fish stocks), chemical pollution, biodiversity change, habitat destruction, alien species invasions, climate-change impacts, and mesoscale variability of the circulation system (TDA, 2007). The present chapter provides an overview of overall assessment for the status of the Black Sea ecosystem and its likely trends of evolution since the implementation of the Black Sea Strategic Plan started with particular emphasis given to 2001-2005. First, the recent state of eutrophication in coastal and shelf waters is assessed in terms of nutrient enrichment levels, limiting nutrients in different water regimes, chlorophyll and dissolved oxygen concentrations. Then, the contribution of chemical pollution is evaluated. It is followed by an assessment of the pelagic and benthic systems and marine living resources. The assessment mainly focuses on the western coastal zone that has been subject to worst environmental degradation with respect to other coastal regions and but it is compared with the interior basin wherever appropriate. Modulation of the ecosystem properties by climate-induced changes is also highlighted.

12.2. Mesoscale variability of the circulation system

Fig. 12.2. A typical structure of the upper layer circulation field deduced from a circulation model using assimilation of altimeter sea level anomaly data. (after Korotaev et al., 2003).?

Primary feature of the Black Sea circulation system is highly dynamic structural organization of the interior cyclonic cell and the Rim Current. The latter flows along abruptly varying continental slope and margin topography around the basin, whereas the interior circulation, formed by several sub-basin scale cyclonic gyres and eddies, evolve continuously due to interactions among these eddies and meanders and filaments of the Rim Current (Fig. 12. 2). Coastal side of the Rim Current comprises a series of recurrent anticyclones. The overall basin circulation is primarily driven by the curl of wind stress throughout the year and further modulated by seasonal evolution of the surface thermohaline fluxes and mesoscale features arising from the basin?s internal dynamics. In addition, fresh water discharge from the Danube and other northwestern rivers contributes to buoyancy-driven component of the basin-wide circulation system. Eddies, meanders, filaments, offshore jets of the Rim Current often introduces strong shelf-deep basin exchanges and two-way transports of biota and chemicals between near-shore and offshore regions.

Flow structure in the northwestern shelf is driven by spreading of the Danube outflow under temporally varying wind forcing. The Danube plume can spread northward or southward along the coast, or is expanded offshore depending on winds, internal dynamics, and initial vorticity of the plume. Southerly? winds cause upwelling along the Romanian ? Bulgarian coast bringing nutrient-rich deep sea waters into the surface layer and promote biological production. On the other hand, northerly winds trap the freshwater plume along the coast and the southward thin boundary current is separated from offshore waters by a well-defined front (Fig. 12.3a) which sometime displays unstable features, exhibits meanders, extends across the wide topographic slope zone and spawns filaments (Fig. 12.3b).

A branch of the Rim current may occasionally protrude into the NWS through outer branch of the Sevastopol eddy and modulates the shelf circulation system. In the case of alternative upstream deflection of the Danube outflow, the southward coastal current system weakens or may totally loose its identity. The river plume may then occasionally be trapped by the anticyclonic Danube eddy that covers the region between Odessa and Constanta (Fig. 12.3b). Other features of the western coastal flow system are the recurrent Kaliakra and Bosporus anticyclones (Fig. 12.2).

Fig. 12.3. SeaWiFS chlorophyll distributions showing two alternative forms of circulation structure in the northwestern shelf; (a) a southward coastal current system during days 152-155 (early June) and (b) a closed circulation system confined into its northern sector during days 194-197 (mid-July), 1998 (after Oguz et al., 2002).

12.3. Climatic regulation of the Black Sea

The Black Sea ecosystem transformations in the 1980-1990s were accompanied with strong decadal scale climatic perturbations. These climatic changes modulated the ecosystem properties concomitantly with the anthropogenic impacts. As shown in Fig. 12.4 (blue curve), amplitude of decadal-scale fluctuations in the annual-mean basin-averaged SST anomaly since the beginning of 1960s was around 1.0 oC. They were locally even more pronounced as, for example, recorded by about 4oC changes in Galata monitoring site along the Bulgarian coast (Fig. 12.4, red curve). These decadal variations were an order of magnitude greater than the global SST changes of ~0.25oC for 1930-2005 (Fig. 12.4, green curve).??

The annual-mean SST variations indicate a succession of decadal-scale cooling-warming cycles on the order of 1.0oC. The period 1937-1957 was characterized by 0.9 oC cooling followed by 1.0 oC warming during 1957-1978, and subsequently two concomitant cooling and warming cycles of ~1.5oC during 1978-1993 and 1993-2002. The system switched to the cooling cycle during 2002-2005.? The switch to the warming phase in the 1990s occurred in the western coast as early as 1988 whereas it was disrupted by the 1997-1998 short-term cooling events.? The strong warming trend in 1993-2002 brought the annual-mean sea surface temperature to the level in the mid-1960s.

Fig. 12.4. Annual-mean sea surface temperature (SST) anomaly changes obtained by in situ measurements at 3 nm offshore of Cape Galata (Bulgaria, after Kamburska et al., 2006; right axis, in red colour) and the basin averaging (left axis, in blue colour) of the Hadley-2 data, and their comparison with the globally-averaged SST fluctuations based on Hadley-2 data (in green; left axis). The Hadley-2 data is described by Rayner et al. (2003).? All data show both the unsmoothed and smoothed (by three-year moving averaging) variations.

The North Atlantic Oscillation (NAO) and the East Atlantic-West Russia (EAWR) climatic indices relate the regional hydro-meteorological properties (such as the air and sea surface temperature and surface atmospheric pressure fields) to the surface pressure differences between the anomaly centres over the North Atlantic and the Eurasia. In general, a mild winter climatic cycle is characterized by relatively high sea surface and air temperatures, higher surface atmospheric pressures, and is correlated with decreasing trends of the NAO and EAWR indices and vice versa for the case of a severe winter climatic cycle. The intimate relationship between the local climate and hemispherical atmospheric motions is evident in Fig. 12.5 by the association of 1981-1993 cooling cycle with increasing trends of both the NAO and EAWR indices. The subsequent warming cycle is explained by decreasing mode of both the NAO and EAWR indices up to 2002, after which neither the NAO nor the EAWR climate index explain well the Black Sea SST variations.

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Fig. 12.5. The changes of annual-mean, basin-averaged sea surface temperature (SST) anomaly and the North Atlantic Oscillation and the East Atlantic-West Russia climate indices.

The SST changes are based on the Hadley-2 data set (Rayner et al., 2003), the atmospheric indices are retrieved from NOAA Climate Prediction Centre data base; http://www.cpc.ncep.noaa.gov/? data/teledoc/telecontents.shtml). All data were smoothed by three-year moving averaging.

12.4. Eutrophication/Nutrient enrichment

River nutrient loads: Following the early 1990s, economical recession in the former eastern block countries indirectly resulted in closure of ecologically ineffective large animal farms (agricultural sources) and of nutrient discharging (e.g. fertilizer) industries. Phosphate content was also reduced in detergents, and nutrient removal from waste water was improved in the countries along the Danube River. Consequently, according to measurements at Reni located 34 km upstream of the Danube delta, the total P-load (TP) experienced a strong reduction from ~60 to 20-30 kt y-1 at the beginning of 1990s and dropped below 20 kt y-1 afterwards as in the case of the 1960?s. The dissolved inorganic nitrogen (DIN) load, measured at Reni, remained around 400 kt y-1 since the beginning of 1990s without any sign of reduction.

Complementary measurements near the mouth of Sulina branch of the Danube River indicated a major reduction of the DIN load from ~700 kt y-1 during the late 1980s to 100 kt y-1in the present decade (Fig. 12.6). 90% of this DIN load was contributed by N-NO3. A roughly three-fold difference between the Reni and Sulina DIN flux estimations may arise due to methodological differences in the measurement techniques, high nutrient uptake in primary production in the Danube delta region as well as mixing and dilution associated with estuarine-type river-sea water interactions. Alternatively, a likely cause of higher DIN flux at Reni may be continuing emissions accumulated in soil stocks in the Danube catchment basin which continue to support high nitrogen load through ground-water emissions. Whatever the cause and the rate of reduction, their 2000-2005 average value was still roughly twice higher than the pristine level prior to the 1960s. The difference in the PO4 load between Reni and Sulina is small and not critical as in the case of DIN.? The SiO4 flux at Sulina reveals an opposite trend; it decreased from 500 kt? y-1 to 100 kt y-1 during the 1980s but increased steadily afterwards up to 500 kt y-1 in 2005 again contrary to considerable silicate retention and decrease in Danube sediment load in response to the construction of reservoirs along the main river and its tributaries after the 1960s (Humborg et al., 1997).? As described below, these trends may be related to the changes in phytoplankton bloom intensity and community structure.

Fig. 12.6. River Danube annual dissolved inorganic nitrogen (DIN), phosphate (P-PO4) and silicate (SiO4) loads into the Black Sea based on the measurements conducted at Sulina. The data are taken from? Cociasu et al. (2008).

Fig. 12.7a. Decadally-averaged changes of surface dissolved inorganic nitrogen (DIN) concentration along the western and eastern coastal waters of the NWS as well as surface N-NO3 concentration in the Romanian shelf (red bars) and the Sulina exit of the River Danube solid dots). The data except at Sulina are amalgamated from several stations.

Nutrient concentrations: During the present decade, DIN concentration along the northwestern and northeastern coasts of the NWS as well as along the Romanian shelf experienced locally either a rising trend or maintained its level in the 1980s-1990s (Fig. 12.7a). Existence of N-NH4 concentration comparable to N-NO3 indicates high emissions from local point sources along the Romanian and Ukrainian coasts of the NWS. DIN concentration at Sulina varying around 50-70 μM during 2000-2005 was still high although it was declined from 350 μM level during the 1990s (Fig. 12.7a). ?Dissolved organic compounds constituted an important nutrient source for the NWS. Monthly DON and DOP measurements at Sulina discharge point during 2004-2005 suggested DON changes from the range of 60-120 μM during autumn, winter and early spring seasons to 20 μM in summer and DOP changes from 4-5 μM to 1 μM (Cociasu et al., 2008). The northwestern coastal waters of the Ukrainian sector were persistently characterized by high DON concentrations that increased from the decadal-mean value 25 μM in the 1980s to 40 μM in the 1990s and the present decade (Fig. 12.7b). Consequently, the western coastal waters presently continue to suffer from both dissolved inorganic and organic nitrogen enrichment and they do not show an apparent status of improvement during the last 10 years. DIN and P-PO4 concentration levels along other coasts (southern, northeastern and northern) were found to be 3-4 times lower than the western coast. The interior basin water column nitrogen structure responded to the decline in the anthropogenic DIN load by reducing peak subsurface nitrate concentration below 6 ?M in the 1990s and below 5 ?M in the present decade (Fig. 12.8).?????

Fig. 12.7b. Decadally-averaged changes of surface dissolved nitrogen (DON) concentration along the western and eastern coastal waters of the NWS.

Fig. 12.8. Temporal variations of the subsurface peak nitrate concentration within the interior basin.

Available data suggest regionally and seasonally varying limiting nutrient conditions along the western shelf waters. In general terms, brackish coastal waters with salinity lower than 17 psu, most influenced by the river discharges, are predominantly P-limited as, for example, reported for the Sulina and Constanta measurement sites due to continuing high nitrogen enrichment. On the other hand, the amalgamated data formed by the N-NO3 and P-PO4 measurements in the Romanian and Ukrainian inner and outer shelf waters show weak N or P limitation (Fig. 12.9) whereas the interior basin is strongly N-limited system. The data also suggest an increasing Si limitation along the western coastal waters due to high N-NO3 concentrations relative to SiO4.

Fig. 12.9. Decadally-averaged changes of N-NO3/P-PO4 ratios in the Ukrainian and Romanian shelf based on the amalgamated data (see Chapter 2 of this report).

Chlorophyll concentration: According to the satellite ocean color data (Fig. 12.10), annual-mean surface chlorophyll concentration in 1998-2007 possesses three-fold higher values in the northwestern region (~3 mg m-3) with respect to the western interior basin (~1 mg m-3). Moreover, in-situ summer chlorophyll-a measurements near the Zmeiny Island reveal summer mean surface Chl-a concentration around 1.0-2.0 mg m-3 (Table 12.1) which are at least twice lower than the mean value of 4.5 mg m-3 for 1980-1995 (Kovalova et al., 2008), therefore supporting a decrease in primary production during the present decade. However, high chlorophyll values up to ~25 mg m-3 are still observed temporarily in spring-summer months. In the subsurface layer, summer mean Chl-a concentration is roughly half of the values measured in the surface mixed layer (Table 12.1). Highest monthly-mean surface chlorophyll concentrations around 2-3 mg m-3 are observed during April-June. The secondary maximum of 2 mg m-3 arises in October-November following the minimum concentration about 1 mg m-3 in August. Thereafter, Chl-a concentration rises from 1 mg m-3 in January up to 3 mg m-3 in April. The corresponding monthly-mean chlorophyll concentration variations provided by the SeaWiFS ocean colour data for the NWS shelf (Fig. 12.10) attains an increasing trend from 2.0 mg m-3 in March to 4.0 mg m-3 in July.? Equally high peak concentrations also arise in November. The satellite data however do not show a well-defined spring peak as in the case of the Zmeiny island data.

Figure 12.10. Average surface chlorophyll concentration for the northwestern shelf and the interior basin obtained from 8-daily 9 km resolution SeaWiFS and Modis ocean colour products after the original data is smoothed by 5 point moving average.

Table 12.1. Ranges and average values of Chl-a concentration (mg m-3) near the Zmeiny Island of the northwestern shelf during summer months of 2003?2007 (after Kovalova et al., 2008).

Surface Layer

Bottom Layer

Range

Average

Range

Average

V-IX?? 2003

0.28-7.75

1.25

0.25-1.26

0.76

VI-XI? 2004

0.22-12.02

2.41

0.26-5.72

1.48

IV-XI? 2005

0.19-28.03

2.90

0.18-2.93

1.03

IV-XI? 2006

0.13-7.29

1.53

0.13-5.55

0.75

IV-XI? 2007

0.13-16.80

1.33

0.15-1.44

0.78

The interior basin depicts a different annual chlorophyll structure (Fig. 12.10). Surface chlorophyll concentration decreases linearly from a peak in November (1.5 mg m-3 as an average of 1998-2007) to a minimum in July (0.75 mg m-3), followed by an increase from August to November again. A weak chlorophyll peak may occasionally exist in spring. This structure implies that the phytoplankton production initiates in September, gradually intensifies and spreads over the basin in October, and finally reaches a basin-wide bloom stage in November. The autumn bloom episode generally terminates in January and is followed by a continuous decreasing trend during winter and spring months. The strong chlorophyll signal in February or March, which was the most robust feature of the annual structure in the 1980s, appears as a slight increase in concentrations by about 0.1-0.2 mg m-3 either in January or February, except no peak in 2002 and its shift to spring in 2001.

Fig.12.11. Long-term variations of spatial coverage of hypoxia in northwestern coastal waters. The data are taken from the Ukrainian National Reports, UkrNCEM.

Fig. 12.12. Changes in summer oxygen saturation values of bottom waters at three locations along the Sf. Georghe transect immediately to the south of Danube discharge zone (after GEF-UNDP Project Report, 2006).

Hypoxia coverage: According to the data shown in Fig. 12.11, the Ukrainian sector of northwestern shelf continued to experience successive large scale hypoxia shocks (> 10,000 km2) once every few years. Although no published data are available after 2001, the hypoxic areas were reported to decrease in the present decade except some short-term events in localized shallow regions upstream and downstream sides of the Danube delta region (e.g. summer 2005). No hypoxia was reported in Bulgarian waters as well as national waters of other Black Sea states. Fig. 12.12 displays the summer 2001hypoxia event in terms of variations of oxygen saturation values at different locations off the Sf. Georghe transect.

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Fig.? 12.13. Long-term variations of winter dissolved oxygen concentration within the layer of density surfaces σt ~14.45-14.6 kg m-3 in the offshore region the eastern coastal waters during 1984-2004 and summer-autumn mean CIL temperature of the interior basin. The oxygen data are provided by Yakushev et al. (2008).

Subsurface oxygen concentration in the interior basin: The level of sub-surface oxygen concentration in the deep region of eastern basin provides an independent assessment for the present state of basin-scale eutrophication. The long-term data of winter dissolved oxygen concentration within the layer of σt ~14.45-14.6 kg m-3 density surfaces (i.e. immediately below the euphotic zone) in the offshore region of the eastern basin during 1984-2004 reveal an increasing trend from 170? μM at 1984 to 300 μM during the early 1990s, and a reverse trend during the 1990s with the values varying in the 240-270 μM range during the present decade (Fig. 12.13). Lower values in the present decade with respect to the early 1990s can however be hardly explained by higher rate of oxygen utilization during the remineralization of organic matter provided the fact that the present decade is known to be less eutrophic and hence less productive than the 1980s. This structure therefore contradicts with a priori expectation from the eutrophication perspective.? A more likely explanation is the degree of ventilation from the surface in response to climatic changes. The former process (i.e. the oxygen utilization) is particularly important during the warm and more productive period of the year and causes oxygen depletion whereas the latter (i.e. the surface ventilation) contributes to its enrichment in winter months. In the case of higher rate of ventilation, more oxygen stored within the oxycline reduces the rate of oxygen depletion in subsequent months and thus support more favourable oxygen conditions during summer months. This link is shown in Fig. 12.14 using the summer-autumn CIL temperature as a proxy variable of climatic changes. The decadal trend of increase of subsurface oxygen coincides with the cold climate period associated with higher rate of atmospheric oxygen flux at the surface. On the contrary, subsequent milder and warmer winter years of the 1990s (i.e. the warming trend of CIL temperature) with more limited atmospheric oxygen supply coincide with the decreasing trend of subsurface oxygen concentration. Cold years 2003-2004 coincide again with relatively higher subsurface oxygen concentrations.

Recalling that the 1985-1993 period was characterized by highest level of plankton production, the accompanying cold winter climatic conditions, on the one hand, pre-conditioned the system for more intense spring production and, on the other hand, prevented excessive oxygen depletion of subsurface levels by storing more oxygen below the euphotic layer, which otherwise would likely cause a broader suboxic layer. Conversely, relatively mild winters after the early 1990s set unfavourable conditions in terms of oxygen ventilation even though biological production was lower than the previous decade.

12.5. Chemical pollution

Discharge of insufficiently treated sewage introduced microbiological contaminants into the Black Sea and posed a threat to human health, development of sustainable tourism and aquaculture. The Black Sea was particularly vulnerable to solid wastes dumped into the sea from ships and coastal towns as any floating or half-submerged waste was inevitably washed ashore. Some beaches have had a high accumulation of garbage presenting a risk to marine animals and humans.

Ballast water and other types of illegal discharges continued to be an important source of petroleum pollution with a high level of spatial heterogeneity. Oil enters the sea as a result of operational discharges of vessels and accidents, as well as through land-based sources. The present level of oil pollution is not high in the open sea but is unacceptable in many coastal areas. The total amount of oil spilt into the Black Sea was generally less than 50 tonnes during 1996-2004 except 260 tonnes in 1997 and 530 tonnes in 2003 (Fig. 12.14). They were discharged by spill accidents of around 10-30 per year with the exception of 61 relatively low spill accidents reported in 2001.

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Fig. 12.14. Total of number of oil spills and amount of oil spilt during 1996-2006 on the basis of data reported by countries to the BSC.

The mean concentration of total petroleum hydrocarbons (TPHs) in general exceeded the Maximum Allowed Concentration limit (MAC~0.05 mg/l) almost everywhere in the sea, but increased up to 25.0 mg/l along tanker and shipping routes between Odessa, Novorossiysk and Istanbul, as it may be inferred from the composite satellite map shown in Fig. 12.15. The extremes in coastal shallow waters (Fig. 12.16) must be a result of local spills from ships calling at ports and bunkering and discharges from the waste water systems of large cities. The current monitoring network is not dense enough to monitor oil spills at a desired level. It will be useful to support field monitoring by routine satellite and/or aircraft images, as this is done in Europe.

Fig. 12.15. Composite map of oil spill anomalies in the Black Sea during 2000-2002 and 2004 based on the images taken by Synthetic Aperture Radars (SARs) of European satellites ERS-2 and Envisat (http://serac.jrc.it/midiv/ maps/). The oil spill density has been spatially normalized to the spill widths. The darker areas signify the high anomaly regions.

Pesticides and heavy metals continue to pollute hot spots near certain well-identified sources. PCBs which are or have been produced for industrial use are now mostly restricted to closed systems, and the use of DDT has been banned or restricted in most countries of the Black Sea. For example, the use of organochlorine pesticides was controlled in the late 1970s in Turkey and Romania, but effective restrictions were not imposed in Turkey until the 1980s. Despite these restrictions, recent studies have shown high concentrations of DDT in Turkish rivers, streams, and domestic and industrial discharges, which indicate their illegal use. The use of these chemicals in other Black Sea countries is currently unclear. Nevertheless, on the basis of available data, pesticide (total DDT and HCH) concentrations in surface waters were typically below their detection limit (0.05 ng/l), except for some very dense patches being detected occasionally. Generally, the present pesticides pollution arises due to their huge amount stored in the agricultural fields or old dilapidated storage places in the past. Concentrations of DDTs, HCHs and PCBs in Black Sea fish and mammals are also high in comparison to those reported for some other regional seas.

Fig.12.16. Mean concentration of total petroleum hydrocarbons in surface waters (0-10m depth) around the Black Sea periphery during 2000-2005 (after TDA, 2007).

Except some hot spot regions with clear anthropogenic influence from the main land-base sources, heavy metal concentrations are generally lower than their Maximum Allowed Concentration (MAC) levels in coastal waters, and close to their natural background values in offshore waters. In particular, the copper and chromium pollutions were wide-spread over the NWS. High chromium concentration was also found along the Crimea coast. A tendency of decreasing maximum mercury and cadmium concentrations in the Danube Delta region has been noted during last 10 years. ?

The rather sparse data set makes it difficult to realistically assess the long-term trends of either TPHs or total DDT and HCH concentrations in sediments. Nevertheless, it may be stated that bottom sediments of almost the entire coastal waters around the sea presently contain high levels of total DDT and HCH pollutions without any clear indication of reduction over the last 13 years of measurements. Sediments in many hot spots contain total DDT and HCH concentrations 5 times higher than their MAC levels, but most serious of them are limited to? the NWS. Highest concentrations of DDTs are traced in lipid rich sediments in the Romanian and Ukrainian coastal waters that are under the influence of River Danube discharge. Elevated concentrations are also reported for sediments in the vicinity of Odessa and Port Constanta. Other pesticides were close to their detection limits except rather high concentrations of hexachlorobenzene in sediments along the Romanian and Bulgarian coasts.

Selected chlorinated compounds in sediments and organisms are ranked as DDTs > HCHs ≥ PCBs > HCBs. As with hydrocarbons, highest concentrations are situated in the Danube delta region and the port Constanta. Among the PCBs, the toxic di-ortho and mono-ortho compounds predominate. The pattern as well as the major sources of PCBs in other countries surrounding the Black Sea are unclear. Concentrations of lindane and other HCH isomers are low in samples from the Ukrainian coastline, Russian Federation and Turkey. Elevated concentrations in samples from Romanian coast stations, under the influence of the River Danube, indicate substantial usage of HCH as a pesticide in the River Danube watershed. The values found at Odessa, the Bosporus entrance region, and Sochi suggest HCH contamination. HCB were found in sediments at much lower concentrations than the other compounds. Its highest values were recorded along the Romanian and Ukrainian coastlines adjacent to the River Danube.

Fig. 12.17. Mean concentrations of total petroleum hydrocarbons in sediments around the periphery of the Black Sea during 1996-2006 (after TDA, 2007).

During the last 10 years, mean concentration of TPHs in bottom sediments of coastal regions was about 1 MAC (50 ?g/g), but much higher concentrations were recorded in sediments collected from large ports, oil refinery and terminals in Romanian, Turkish and Russian waters (Fig. 12.17). They generally decreased offshore. Irregular and often patchy sampling in many parts of the sea greatly limited a better evaluation of the TPH pollution. A more systematic monitoring program is desired for a better description of petroleum hydrocarbons pollution in bottom sediments especially in the vicinity of main oil sources.

Radioactive substances which have been introduced to the Black Sea by the Chernobyl accident in 1986 do not pose a risk any more.

12.6. Biodiversity change, habitat destruction, alien species invasions

Phytoplankton: The annual-mean phytoplankton biomass over the Ukrainian, Romanian and Bulgarian shelf waters (Fig. 12.18a) experienced a decreasing trend from ~10 gm-3 during the late 1980s and the early 1990s to less than 4 g m-3 during the 2000s. Relatively high values greater than 20 g m-3, however, occasionally measured in hot spot regions along the entire coast, an example of which is shown in Fig. 12.18a near Batumi (Georgia) in 2005. A decreasing trend of phytoplankton biomass from 20 g m-2 to 4 g m-2 was also observed in interior basin up to 2002 followed by an increase to more than 10 g m-2 in the subsequent years (Fig. 12.18b). Assuming that phytoplankton biomass in western coastal waters is homogeneous over 10-15 m layer, its integrated biomass of 40-60 g m-2 is roughly five-folds higher than the interior waters biomass that imply extensive ongoing phytoplankton production within the inner shelf waters of the western basin. On the other hand, a two-fold increase in species diversity from roughly 20 to 40 (Fig. 12.19a), decreasing phytoplankton:zooplankton biomass ratio (Fig. 12.19b) together with diminishing bloom frequency and tendency of shift of annual maximum algal development from summer to the classical spring and autumn forms during the present decade indicate a tendency of algal community towards its normal status. In fact, the shifts in phytoplankton taxonomic composition have become more and more evident since 2000. The blooms of non-traditional species (Dactylosolen fragilissimum, Pseudosolenia calcar-avis, Akashiwo sanguinea, Emiliana huxleyi, microflagellates) are more frequently observed and a high number of new species have successfully adapted to the Black Sea environment, some of them however potentially toxic.

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Fig.12.18a. Long-term variations of annual-mean phytoplankton biomass (g m-3) averaged over all stations in the Romanian (RO), Bulgarian (BG), Georgian (GE) shelves as well as the coastal northwestern sector of Ukrainian shelf (NWS-UA, after Nesterova, 1987, see Chapter 5 of this report).

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Fig. 12.18b. Long-term variations of summer-autumn mean phytoplankton biomass (g m-2) (vertical bars; after Mikaelyan, 2005), the mean CIL temperature (oC) (blue dots; after Belikopitov, 2005) averaged over all stations within interior basin and mean winter (December-March) sea surface temperature (SST) as an average of Hadley2, NCEP-Reynolds and Pathfinder5 data sets. The phytoplankton biomass is expressed in terms of euphotic zone integrated values.

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Fig. 12.19a. Long-term changes in species number contributing to annual phytoplankton biomass along the Bulgarian coastal waters (after Moncheva, 2005).

Diatiom/dinoflagellate biomass ratio is normally considered as an indicator for the change in phytoplankton taxonomic structure. Its classical spring-summer value of 10:1 for an undisturbed system was used to be maintained in the Romanian coastal waters during the 1960s and 1970s by 92% and 75% contribution of diatoms, respectively. This ratio then altered in favor of dinoflagellates during the 1980s when its biomass constituted almost 60-70% of total phytoplankton (Fig. 12.20). The diatom constituted more than 50% of the total phytoplankton during the 1990s whereas dinoflagellates became the dominant group again during the recent decade. Similar changes were also observed in the Bulgarian coastal waters and within the interior basin.?

Fig. 12.19b. Long-term changes annual-mean phytoplankton to edible zooplankton biomass ratio along the Bulgarian coastal waters (after Moncheva, 2005).

Fig. 12.20. Long-term change in percentage of biomass of main algal groups in Constanta monitoring station during 1986-2005 (after Boicenco, see Chapter? 5 of this report). ????????

The shift in phytoplankton species composition from diatom (siliceous) to dinoflagellates (non-siliceous) during the 1980s is consistent with the decreasing silicate concentration and thus reduction in Si:N ratio of the Danube nutrient load during the 1980s. As the Danube SiO4 load increased in the 1990s, diatoms were no longer limited and started dominating the community structure against dinoflagellates. In the present decade, decreasing SiO4 load (except 2005) led to domination of the community structure by dinoflagellates again.? Furthermore, cooler (warmer) spring-summer conditions in the 1980s (1990s) provide growth advantage for dinoflagellates (diatoms) (Stelmakh, 2008).

The phytoplankton data from the interior basin indicate domination of phytoflagellates and coccolithophores in the annual bloom structure during the present decade. The species shift towards carbonate-producing coccolithophores in coastal waters during May-June has significantly affected sea water chemistry in terms of alkalinity and pH. Predominance of small-sized flagellates during the recent years may be a major reason for the proliferation of gelatinous zooplankton (e.g. Noctiluca scintillans) at the expense of edible mesozooplankton and fish eggs and larvae.???

Trends in phytoplankton biomass may not always be a firm indicator for the state of eutrophication due to strong modulation of bloom intensity and species structure by climate-induced changes. For example, anthropogenic-based nutrients that were accumulated into the subsurface waters of the interior basin and/or sediments of the shelf waters are brought into the surface layer more effectively in cold winters that then promote more intense new production-based spring blooms and subsequently stronger regenerated production in summer months. This is clearly shown by the correlation between increasing and decreasing trends of interior basin phytoplankton biomass and the cooling and warming phases of the mean May-November CIL temperature during the 1980s and 1990s, respectively (Fig. 12.18b). The subsequent increase of phytoplankton biomass in 2003-2007 may also be explained by the recent climatic cooling trend. Moreover, the phosphorus limitation constitutes as an additional factor for the decrease of phytoplankton biomass along the western coastal zone during the 1990s and the present decade.

Even if the phytoplankton biomass has been improved recently, it does not indicate a stable structure; instead it implies a transitional phase with fragile ecological conditions under relatively high nutrient concentrations. ?????

Bacterioplankton: The annual-mean bacterioplankton abundance within the northwestern shelf during 1979-2008 (Fig. 12.21a) resembles closely the long-term changes in phytoplankton biomass. It reveals an increasing abundance from the average value of 1.2 million cells ml-1 during the late 1970s and the early 1980s (the range: 0.3-2.6? million cells ml-1) to 3.3 million cells ml-1 (the range 1.0-7.3 million cells ml-1) in 1990-1991. It was followed by an abrupt drop to ~2.5 million cells ml-1 in 1993-1994 and a steady decreasing trend to 1.5 million cells ml-1 up to 2008. The average bacterioplankton abundance was therefore reduced during 2003-2008 by more than twice with respect to 1990-1992. This reduction was most likely caused by the decrease in total concentration of autochthonous and allochthonous organic matter that are more easily assimilated by bacteria; thus implying a reduction in organic pollution in the northwestern Black Sea. This should be connected to the decrease in the intensity of algal blooms and lower mortality rates in bottom fauna. Higher abundance was particularly observed in the vicinity of Danube delta. The measurements in the Bulgarian coastal zone also showed a stable annual abundance remained around 1.0 million cells ml-1 since 1994.

The NWS bacterioplankton abundance (Fig. 12.21b) attains lowest values in winter (January-February) and highest in summer under high organic matter accumulation in water column. During the intense eutrophication phase (1983-1997), abundance greater than 2 million cells ml-1 prevailed from March to October with the highest population close to 3 million cells ml-1 in August. During 2004-2007, maximum abundance reduced to 1.5 million cells ml-1 and summer abundances varied around 1 million cells ml-1 from April-to-September.

Fig. 12.21a. Long term annual-mean changes of bacterioplankton abundance in the surface layer of northwestern and Bulgarian coastal waters (redrawn from Kovalova et al., 2008).

?

Fig. 12.21b. Long term monthly-mean changes of bacterioplankton abundance in the surface layer of northwestern coastal waters in the Black Sea (redrawn from Kovalova et al., 2008).

Edible Zooplankton: The annual-mean edible zooplankton biomass formed by averaging of the Ukrainian, Romanian and Bulgarian data sets exhibited a declining trend from ~300 mg m-3 in 1960 to 20 mg m-3 in 1990, persisted this level up to 1995, and then fluctuated interannually within 50-200 mg m-3 range during 1996-2004 (Fig. 12.22). These fluctuations were mostly provided by the intermittent recovery of edible zooplankton (up to ~300 mg m-3) within the Romanian shelf contrary to only a slight improvement (~100 mg m-3) in the Ukrainian NWS and the Bulgarian shelf. According to this amalgamated data, the highest biomass registered within 1996-2004 was almost half of the biomass attained prior to the 1970s.

On the other hand, edible zooplankton biomass followed a different track of changes in the northeastern basin; it fluctuated around 10?5 g m-2 during 1960-1990, maintained its minimum level (2.0 g m-2) during 1991-1993, and then experienced a pronounced rising trend to 20 g m-2 in 2000-2004 and 25.0 g m-2 in 2005-2008 (Fig. 12.22). Its values during the present decade were the highest ever registered since the 1960s. Assuming that zooplankton population is uniformly distributed within the upper 50 m layer, integrated biomass of the western coast during 1996-2004 varied between 2.5 and 7.5 g m-2 that were comparable with the Cape Sinop? but substantially lower than the northeastern basin (Fig. 12.22).?

Fig.12.22. Long-term variations of the annual-mean edible zooplankton biomass in the northeastern basin (g m-2) and the western coast (mg m-3) obtained by averaging the Romanian, Bulgarian, and the northwestern Ukrainian data sets. Also included for comparison is the edible zooplankton biomass (g m-2) measured near the Cape Sinop in central part of the Turkish coast (after? Shiganova et al., see Chapter 6 of this report).

Although fodder zooplankton biomass has not yet increased to a level observed in the 1970s in the NWS and western coastal waters, its community was partially recovered in terms of species diversity. The community structure was re-organized by an increase in abundance and biomass of copepods and cladocerans, such as A. tonsa, P. mediterranea, C. euxinus and A. patersoni which were almost absent during 1980s-1990s. The extinct species P. mediterranea, being an indicator of non-eutrophic waters, has re-appeared since 2000 as a sign of positive ecosystem changes. Similar changes were also noted within the northeastern basin.

Fig. 12.23 depicts distribution of the summer edible zooplankton biomass over the basin based on the compilation of all the available data during 1954-1995. It reveals considerable patchiness in accord with the meso-scale circulation structure (Fig. 12.2). Biomass variations follow closely meanders of the Rim Current with higher biomass within coastal anticyclonic eddies at onshore side of meanders. Its most distinctive example is shown near the southeastern corner of the sea occupied by the well-known quasi-permanent Batumi gyre.?????

Gelatinous zooplankton: According to recent observations (1998-2004), Mnemiopsis biomass had a decreasing trend following its population control by Beroe after 1998. Nonetheless, M. leidyi can occasionally be abundant in the northwestern and western coastal waters (Figs. 12.24), in contrast to deeper part of the western shelf and the northeastern basin where the share of A.aurita was increased due to its competitive advantage under low Mnemiopsis populations. As one of the worst cases, edible zooplankton biomass in the Danube delta region constituted only 10% of the total zooplankton structure during 2003-2007; the rest was dominated by the combination of Mnemiopsis, Aurelia and the opportunistic species N. scintillans. On the premise of low edible zooplankton and high gelatinous and opportunistic species, the western-northwestern inner shelf waters therefore do not show a stable zooplankton structure within the present decade, but a sign of recovery of mesozooplankton community structure is well-marked within the northeastern basin.

Fig. 12.23. Distribution of summer edible zooplankton biomass (mg m-3) during 1954-1995 (after Temnykh, 2006).

Fig. 12.24. Mean Mnemiopsis leidyi abundance (ind.m-3) in the Northeastern (NE), North-Western (NW), and Western (W) Black Sea inshore and offshore waters during the summer 1998-2004 (redrawn from Kamburska et al. 2006).

As for the long-term variations of phytoplankton, zooplankton biomass and community structure also appear to be strongly regulated by climatic variations. Relatively mild years with warmer winter temperatures favour more efficient Mnemiopsis and edible zooplankton growth, whereas severe years with colder winter temperatures limit edible zooplankton production albeit producing stronger spring phytoplankton blooms and promote more favourable N. scintillans and A. aurita development. The spring temperature conditions are particularly critical for the intensity and species succession of zooplankton production. Mnemiopsis attained higher biomass when August surface temperature was relatively high as in the case of 2000-2001 and 2005 or lower biomass as in the case of relatively cold August temperatures during 1996-1998 and 2003-2004.

Macrophytobenthos: The red algae Phyllophora field in the northwestern shelf was known to be one of the most extensive macrophytobenthos habitats in the world. It was not only an important generator of oxygen but also the nucleus of benthic community involving more than 100 species of invertebrates and more than 40 species of fish. Following the deterioration of environmental conditions since the early 1970s as a combination of reduced transparency, lifting of mud particles in the water column during bottom trawling and hypoxia, the settlement size and stock of phyllophora field reduced from about 9 million tons to 8 thousand tons in 2000. Phyllophora harvesting therefore ceased practically after 1996. The recent observations indicated a sign of their re-establishment within the outer shelf whereas no apparent recovery has yet been evident close to the mouths of Danube and Dniester Rivers in particular and shallow coastal zone of the NWS in general. Its total harvesting of 0.5 thousand tons during the recent years had no significant commercial value, but suggests their ongoing degradation. A similar deterioration of Phyllophora biomass also continues along the northeastern coastal zone. For example, its biomass of 1.4 kg m-2 along 20 m isobath during the 1970s reduced to 0.5 kg m-2 during 1998 and disappeared during 2005. The same also holds in shallower regions.

Fig. 12.25a. Long-term change of total macrophyte biomass (kg m-2) in the northwestern shelf dominated by small, opportunistic species (after Minicheva, see Chapter 7 of this report).

Due to intense eutrophication, Cystoseireta phytal zone has been reduced to a narrow inshore strip shallower than 10 m due to the lack of sufficient light for photosynthesis in deeper regions. Beyond 10 m depth zone, large perennial macrophytes with a thick talus and longer life cycle were replaced with a few small branchy, filamentous, opportunistic-type algae species having rapid growth but relatively short life cycle. Nevertheless, the overall biomass of opportunistic species group had a declining trend by the beginning of 1990s and their present level suggested a three-fold reduction (Fig. 12.25a). Similarly, along the northeastern coast, Cystoseira fields that were used to stretch up to 20-30 m in the 1970s with biomass >3.0 kg m-2 were limited into the innermost 5 m zone during the 1980s (Fig. 12.25b). The present status shows a slight recovery at depths shallower than 10m zone (Fig. 12.25b). Floristic diversity of macrophyte communities in Zernov?s Phyllophora field started increasing even though the tendency of increase in Ochrophyta species is minor with respect to ongoing intensive development of ecologically active filamentous algae in relation to the increase of transparency and availability of high nutrient content in the bottom sediments (Fig. 12. 25c). In spite of such positive signs, it is still difficult to assert an appreciable basin scale restoration. Full recovery of historical Phyllphora field is still not evident. Its coverage both in winter and summer is less than 10% with respect to the pristine state, and its role as habitat was taken over by filamentous algae.

?

?Fig.12.25b. Cystoseira spp. biomass at different depths along the northeastern coastal zone during 1970, 1988 and 2005 (after Kucheruk, 2006).??

Fig.12.25c. Changes in floristic diversity of macrophyte communities in Zernov?s Phyllophora field (after Friedrich et al., 2008).

Macrozoobenthos: The most notable changes in zoobenthos community of the 1980s and 1990s in response to intensifying eutrophication and sustained organic enrichment of sediments were lower species diversity, reduced abundance and biomass of benthic populations, and thus a more simplified community structure dominated mostly by opportunistic and invasive species with high total abundance but low total biomass, increasing role of hypoxia-tolerant groups (bivalve molluscs), high fluctuations of populations. Despite such severe changes, observational studies since the mid-1990s were limited and were based on random samplings with irregular periodicity. The measurements suffered from deficiencies in sampling quality and processing, organism identification, lack of general consensus on benthic biodiversity methodology, and insufficient experts. Therefore, the current state of knowledge on the existing state of zoobenthos structure involves many uncertainties to make a reliable assessment.

Available data for the western shelf suggest a slight improvement of zoobenthos community structure in terms of species number during the last 10 years (Fig. 12.26). Some species sensitive to hypoxia which became almost extinct started re-appearing. But, the recovery of the crustaceans is incomplete despite their population increase. The mussel Mytilus galloprovincialis population seems to grow under more favourable conditions as they can sustain more than one year life cycle. The current abundance level of opportunistic molluscs? species, the predatory gastropod Rapana venosa, the bivalves Anadara inequivalvis and Mya arenaria, however continue to dominate the macroobenthos system due to rich trophic resources and their hypoxia tolerance.

Fig. 12.26. Temporal changes in species diversity of total macrozoobenthos community in the Romanian pre-Danubian and Constanta sectors (left) and the Bulgarian shelf (right) (after Abaza, Todorova et al., see Chapter 8 of this report).

As these modifications signaled beginning of the rehabilitation trend, the general state of this biotic component of the marine ecosystem is still fragile over large areas of the Ukrainian and Romanian shelves and represents clear symptoms of undesirable disturbances, such as patchiness, domination of the zoobenthos system by opportunistic and hypoxia tolerant species as indicators of organic pollution. Shallow, coastal regions remain to be vulnerable to anthropogenic disturbances as compared to offshore areas deeper than 30-50m. The muddy bottom biocoenoses of Modilus phaseolinus at deeper than 50 m has not yet recovered due to impact of hypoxia, opportunistic species, and degradation of bottom by dredging and trawling. Therefore, there are great deals of uncertainty to claim the recovery. On the other hand, the classification algorithm based on the empirical AMBI model (Fig. 12.27) suggests a rather optimistic view that even the Danube delta region has rather moderate pollution level and most part of the NWS is in ecologically good conditions. The conditions gradually progress to the south along the western coast and to the east away from the source region of the pollution and eutrophication.

Fig. 12.27. Recent ecological state of he northwestern and western shelves according to the AMBI classification. Yellow and green colours signify moderate and good ecological state, whereas the brown spots are degraded regions of macrozoobenthos (after GEF-UNDP Project Report, 2006).

Introduction of Beroe and its predation on Mnemiopsis introduced a major transition in macrozoobentic populations. As shown in Fig. 12.28a for the northeastern coastal zone, over-comsumption of bivalve larvae and the subsequent reduction in the settlement of young bivalves observed during the 1990s were ended after the weakening of Mnemiopsis population. This led to mass settlement of opportunistic alien Bivalvia species Anadara inequivalvis larvae that is a major competitor of the native species Chamelea gallina. Simultaneously, the niche emptied by Mnemiopsis was immediately occupied by the opportunistic invasive predator Gastropod species Rapana venosa. Starvation due to food shortage for such high populations and their predation by Rapana venosa concomitantly led to their population decline which was followed by the population decline of Rapana due to food shortage. The opportunistic polychaeta group took advantage of these conditions in the absence of Rapana and increased at a significant level. It is not clear whether this transient system observed during 2000-2005 is gradually stabilizing in recent years or still continuing to persist.

Fig. 12.28a. Changes in dominant zoobenthos species biomass ( g m-2) at the 10-30 m depth range of northeastern Black Sea coast during 1936-2005 period (after Kuchreruk, 2006).

Fig. 12.28b. Species rank of macrozoobenthic population indicating its overwhelming domination by worms in the northwestern shelf (after Friedrich et al., 2008).

The 2008 Poseidon cruise in the NWS indicated a similar spectacular population development of Polychaeta species on soft sedimentary and hard substrate (Friedrich et al., 2008). As they formed 70% of the benthic population, filter feeders constituted only 9% that is a typical indication for eutrophication (Fig. 12.28b). Overall findings of the cruise were small recovery of macrozoobenthos community, strong biomass perturbations, high ecological pressure in coastal areas especially the vicinity of Danube and Dniestr discharge regions, ongoing ?high pressure from Mya arenaria, Anadara inaequivalvis, Rapana venosa survivors, and domination of the macrozoobenthos community by Polychaeta species.

12.7. Status of marine living resources

Pelagic fishes in general and their small-sized plankton-eating types in particular are most abundant species in the Black Sea ichthyocenosis. The total catch main target species European anchovy (Engraulis encrasicolus) constituted 31-75% of the total Marine Living Resources (MLR) during the last 15 years. European sprat (Sprattus sprattus), Mediterranean horse mackerel (Trachurus mediterraneus), Atlantic bonito (Sarda sarda) and bluefish (Pomatomus saltatrix) are the other pelagic fishes in terms of fishing value. The latter three species are large-sized predators which migrate into the Black Sea from the Marmara and Aegean Seas for feeding and spawning in spring and return their native places for wintering in late autumn. The catch around 350,000 ? 100,000 tons suggest partial recovery of major pelagic species after the fishery collapse at 1991 (Fig. 12.29).

From the fisheries perspective, the most important demersal fish species in the Black Sea are whiting (Merlangius merlangus), picked dogfish (Squalus acanthias), turbot (Psetta maxima), striped and red mullets (Mullus barbatus, M. surmuletus), four species of the family Mugilidae, including so-iuy mullet (Mugil soiuy). The total catch of these demersal fish species had a tendency of reduction after 2000. Its present catch size is approximately half of the 1990s (Fig. 12.29).

Among fishes by capture volume, the anadromous fish species pontic shad (Alosa pontica) and three sturgeon species Acipenser gueldenstaedtii, Acipenser stellatus, Huso huso take the last place, but their high consuming and economical value determines their specific role in the structure of the MLR. Stocks of anadromous fishes are formed mainly by the Danube populations. The catch data (Fig. 12.29) suggested their order of magnitude decline from about 5000 tons in 1994 to 500 tons in 1999-2001. A slight increasing trend of their annual catch after 2000 was due particularly to the recovery of Pontic shad.

Fig. 12.29. Total catches of main anadromous, demersal and small pelagic fishes in the Black Sea during 1989-2005. The demarsal and pelagic fish catch values need to be multiplied by 10 and 100 to get the observed magnitudes, respectively (after Shlyakhov and Daskalov, see Chapter 9 of this report)

?

During 2000-2005, the most significant threats for fish resources appear to be the illegal fishing and use of destructive harvest techniques as well as the lack of regional cooperative management of fisheries, in addition to eutrophication-induced instability in the food web structure. At present, no recovery of sturgeons spawning and nursery habitat occurred, restocking size of the Dnieper sturgeon populations reduced considerably and the state of sturgeon stocks deteriorated definitely after 1999 with the possibility of collapse not being excluded. The state of Danube shad stocks did not improve; nevertheless the situation is less disastrous as compared to sturgeons. The sprat, anchovy, picked dogfish, and mullet stocks partially recovered in 1995-2005, but the current level of relatively high fishing efforts and catches impose a risk of deterioration of their stocks. The horse mackerel stock continues to be in a depressed state with low stock size and there is no sign of its recovery. The whiting and turbot stocks are exploited rather intensively and declining.

Among the mollusks, the clams (Chamelea gallina, Tapes spp.), the Mediterranean mussel (Mytilus galloprovincialis), and the sea snail (Rapana venosa) have the greatest commercial value. The former two species are harvested only by Turkey and the latter species by all countries of the region except Romania. In 2000?2005, mussel harvesting has had a decreasing trend in the Ukrainian sector but as a whole the state of mussels improved in the Black Sea (Fig. 12.30).

?Fig. 12.30. Total catch of main mollusks in the Black Sea in 1989 -2005 (after Shlyakhov and Daskalov, see Chapter 9 of this report).

The current status (2000-2005) of the MLRs, in general, suggests an improvement with respect to the collapse period (1989-1992), but the overall situation is inferior when compared with the baseline state (1970-1988). The highly variable stock dynamics and lack of effective control measures may quite likely lead to sharp stocks decline in the future. In order to avoid this risk and to achieve sustainable fishery development, implementation of a regional management strategy is essential.

The harbour porpoises (Phocoena phocoena relicta), common dolphins (Delphinus delphis ponticus) and bottlenose dolphins (Tursiops truncatus ponticus) are the top predators without any natural enemies in the Black Sea except humans. Their populations were badly damaged during the last four decades due to anthropogenic-induced habitat degradation, depletion of food resources and commercial and intentional killing until the early 1980s. They are supposedly protected by the international agreements, but in practice their conservation status has not been adequately assured yet.

12.8. Conclusions

Briefly, our assessments indicate a tendency of improvement and rehabilitation of coastal ecosystems of the Black Sea after 1995 under constraints for implementation of environment politics and restructured economic activities. The trends of improvement are visible both for water quality parameters and structural and functional properties of biota, when compared with conditions observed from the mid 1970s to the early 1990s. On the other hand, oil pollution still appears to be an ongoing concern along major shipping routes and in coastal areas around river mouths, sewerage outfalls, industrial installations and ports. There is no evidence of significant heavy metal, pesticides and other persistent organic pollutants (such as polychlorinated biphenyls, PCBs, or polyaromatic hydrocarbons, PAHs) in surface waters although elevated levels of these substances in hotspots around industrial centres and ports suggest their continuous monitoring. Following the 1986 Chernobyl accident, the present level of radioactivity does not pose a health hazard to humans and environment but it is important to monitor its changes. Bottom sediments in many coastal regions around the sea continue to possess high levels of TPHs, DDT and HCH pollutions without any major reduction over the last 10 years. Nevertheless, conditions gradually progress to the south along the western coast and to the east away from the source region of the pollution and eutrophication.

The pelagic ecosystem of western Black Sea coastal waters improved noticeably due to weakening of anthropogenic pressures. It is inferred by reduced nutrient inputs and fewer algal blooms, lower algal biomass, recovery of some algal populations, increasing plankton biodiversity, decreasing opportunistic and gelatinous pressures, and re-appearance of some native fodder zooplankton and fish species and increasing edible zooplankton biomass. The current relatively low nutrient inputs, especially phosphorus, were mainly due to the economic recession after the collapse of the former Soviet Union. The phosphorus limitation prevails most notably along the coastal zone whereas the nitrogen limitation dominates within the outer shelf and deep basin. The climatic warming during the 1990s and the early 2000s also played an important role for the limitation of primary production. Its relative contribution to the overall improvement of the pelagic system of the western coastal and shelf waters remains to be substantiated by the modeling studies. A switch to the cold climatic conditions in the future (as in the 1980s) may promote more intense phytoplankton production and thus disturb the present quasi-stable pelagic ecosystem structure.

The prominent changes were encountered in the structure of benthic communities of the Romanian and Ukrainian coastal waters. However, recovery of the benthic ecosystem appears to be less certain although an improvement on regeneration of macrophytobenthos and macrozoobenthos is suggested by the available data. In the western Black Sea, large areas of the seabed that had been suffering from anaerobic conditions ? a clear symptom of eutrophication ? started now returning to conditions prior to the 1970s. Hypoxic events are now less severe and less frequent than they were used to be in the past. The available data also show some unavoidable indications that the present status of benthic ecosystem is highly fragile and susceptible to further anthropogenic and environmental impacts. The regions shallower than 30-40 m depths still show symptoms of some undesirable disturbances, the most important of which is exerted by the alien opportunistic species such as bivalve species Mya arenaria, soft-clam species Anadara inequivalvis, gastropod species Rapana. Once again, higher organic load to the benthic community which likely develops during cold-climatic conditions may further disturb the benthic structure.?

Fish stocks over the basin are still out of balance, mainly as a result of overfishing but also due to eutrophication. For example, eutrophication-induced unfavourable conditions reduced sharply catches of demersal fish with high commercial value such as flounder and turbot and replaced them with large quantities of small pelagics such as sprat in the western shelf. As a consequence, the Ukrainian and Romanian fishing fleet in the Black Sea almost collapsed. The additional impact of overfishing exacerbated the decline of high trophic level fishes relative to low trophic level fishes and multispecies fishery is unsustainable during the present decade. Anchovy remains to be the top predator species of the Black Sea ecosystem together with sprat along the western coast. Illegal fishing and destructive harvest techniques, lack of regional cooperative fishery management, eutrophication-induced instability of the food web structure constitute ongoing major threats for fish resources.

Fig. 12.31. Long-term changes of Q-value defined as the ratio of pelagic fish catch (in ktons y-1) to phytoplankton biomass (in mg? m-3) as a measure of ecosystem vulnerability to the changes by external stressors (after Yunev et al., 2008).

Recently, Yunev et al (2008) proposed a diagnostic method to assess the long-term improvement of pelagic ecosystem. It was based on the ratio of pelagic fish catch (in ktons y-1) to phytoplankton biomass (in mg? m-3) referred to as Q-value to measure efficiency of the high energy food web chain (phytoplankton-zooplankton-small pelagic fish) since the 1960s. Phytoplankton biomass was constructed from the station network of all available measurements from the Bug River region in the north to the Cape Kaliakra region in the south. The Q-value (=0.4) was highest during the pristine state and deteriorated gradually up to 0.10 during the early 1990s of anchovy collapse and Mnemiopsis population outburst. Thereafter, it increased to 0.21 during the 1990s and 0.23 during the present decade in response to decrease in phytoplankton biomass and increase in small pelagic stock recovery. The current Q-value of 0.23 was still roughly half of its pristine value and indicated low resilience of the Black Sea ecosystem and high vulnerability to external stressors.

The present ecosystem structure is still different from that documented during the 1960s, and most likely it will never revert back to the pristine state. A more likely scenario is adaptation of the system to new conditions where it will eventually be stabilized. However, it is too soon to assert its stabilization today due to prevailing relatively high nitrogen concentration in the water column and sediment. The complexity and inherent nonlinear response of the ecosystem to external drivers and their internal feedbacks make unclear how the pelagic and benthic systems will respond to further stresses that may likely be introduced by climate changes, future agricultural and industrial development as economies of the riparian states recover. Its stabilization partly depends on natural evolution of the system under the concurrent impacts of climate change; eutrophication level, invasive species populations, and sustainable consumption of fishery resources. But it may partly be controlled by a carefully designed and implemented integrated and adaptive management strategy that ultimately needs to take firm decisions by policy-makers in the riparian countries.

Restoration of ecosystems is generally a long-lasting process that depends on the accomplishment of the conservation, protection and management measures both at national and regional level. In this respect, stress reduction interventions should be implemented in order to achieve improvement of environmental conditions in the coastal zone of the Black Sea and the sea itself. The most critical ones are the reduction of the terrestrial nutrient load from the catchment basin by investing in high technology waste-reduction projects and intensive agricultural practices, firm control on commercial fishery by effective regulation of trawls and dredges.

Moreover, the present assessment study indicates some gaps in our knowledge due to the absence of sufficiently comprehensive monitoring data. ?For the success of ecosystem restoration, routine monitoring of the key ecosystem indicators, e.g. set by EEA within the DSPIR framework, should be effectively implemented. This approach will further set a basis for the policy-relevant assessment of the state of the Black Sea environment in the EU context. The DSPIR protocol, however, may require some adaptations to the Black Sea conditions in terms of network of coastal stations, sampling frequency, and sampling depths in order to allow detection of temporal trends and inter- comparison of different areas. To this end, measurements of nutrients, oxygen, chlorophyll concentrations, as well as phytoplankton and zooplankton biomass, abundance and diversity need to be measured on monthly basis at some selected critical sites around of the basin. Also of critical importance is to monitor them not only in surface waters but also below the seasonal thermocline, and close to the bottom. Because majority of processes governing the pelagic ecosystem take place at time scales less than a month either in the surface layer or different parts of sub-surface layer, such high temporal resolution in observational strategy is indeed necessary. Either temporally, spatially and/or vertically coarse resolution measurements may be adequate for a stable ecosystem but will indeed carry a high risk of false assessments for the unstable Black Sea ecosystem.

Monitoring benthic communities needs to be designed to detect subtle changes in community structure through some indices and environmental conditions that drive these changes (e.g. sinking organic carbon flux, organic carbon content in sediments, deep-water oxygen concentration). The most practical approach is to choose some indicator species among the groups known to be opportunistic, disturbance-sensitive or insensitive. Great natural variability of the benthos requires seasonal monitoring at critical sections with many replicate samples. Monitoring chemical pollution level in sediments may be sufficient once a year. Large uncertainty exists on the amount of nutrients entering from the atmosphere and sediments, which therefore need to be monitored regularly around the basin. For example, the continuous measurement on the Zmeiny Island located 40 km away from the Danube Delta and therefore isolated from the local sources of atmospheric pollution indicated approximately 240 ktons y-1 and 16 ktons y-1 of atmospheric nitrogen and phosphorus fluxes when extrapolated over the Black Sea (Medinets and Medinets, 2008). Similar measurements during 2004-2005 in Sevastopol revealed 240 ktons y-1 nitrogen load (Chaykina et al., 2006). These figures are comparable with the loads supplied by the River Danube in recent years.

Ecosystems damaged by human actions for long periods of time show very slow recovery rate later despite of rehabilitation efforts. For example, after all efforts and progressive implementation of EU Directives, so far there has been only limited reduction in eutrophication of the Baltic and North Seas. ?

References

Chaykina A.V., Dolotov V.V., Ilyin Y.P., Konovalov S.K., Kuznetsov A.S., Repetin L.N., Voitsekhovich O.V. (2006) Observational studies of nutrient loads on the Black Sea with atmospheric precipitations. In: Proceedings of The First Biannual Scientific Conference: Black Sea Ecosystem 2005 and Beyond, May 8 2006, Istanbul, Turkey.

Cociasu, A., Lazar, L., Vasiliu, D. (2008) New tendency in nutrient evolution from Romanian coastal waters. Cercetari marine, 38, 7-23.

Friedrich, J., Delacruz, J., Gilbert, A., Lowe, C. Mee, L (2006) Analyzing ecosystem state changes on the north-western Black Sea shelf with conceptual models. In: Proceedings of The First Biannual Scientific Conference: Black Sea Ecosystem 2005 and Beyond, May 8 2006, Istanbul, Turkey.

Friedrich, J., et al. (2008) State of the benthic ecosystem on western Black Sea shelf in early spring 2008. In: 2nd Biannual and Black Sea Scene EC project joint conference on climate change in the Black Sea ? hypothesis, observations, trends, scenarios and mitigation strategy for the ecosystem. 6-9 October 2008, Sofia, Bulgaria.

GEF-UNDP Project (2006) Trends in nutrient loads from the Danube river and trophic status of the Black Sea: Extended version of a briefing note originally provided to GEF Council on 6 June 2006. Joint Report of the GEF-UNDP Black Sea Ecosystem Recovery Project and the GEF-UNDP Danube Regional Project. 22pp+ Figures and Tables (21pp).

Humborg, C, Ittekkot, V., Cociasu, A., Bodungen, B.V. (1997) Effect of Danube River dam on Black Sea biogeochemistry and ecosystem structure. Nature, 386, 385-388.?

Kamburska L., Schrimpf W., Djavidnia S., Shiganova T., Stefanova K., 2006. Addressing the ecological issue of the invasive species, Special focus on the ctenophore Mnemiopsis leidyi (Agassiz, 1865) in the Black Sea. EUR 22310 EN, JRC-EC Publication office, 59 pp.

Korotaev, G.K., Oguz, T., Nikiforov, A., Koblinsky, C. J. (2003) Seasonal, interannual and mesoscale variability of the Black Sea upper layer circulation derived from altimeter data. J. Geophys. Res.

Kovalova, N.V., Medinets, S.V., Konareva, O.P., Medinets, V.I. 2008. Long-term changes of bacterioplankton and of chlorophyll ?a? as indicators of north-western part of the Black Sea ecosystem changes last 30 years. In: 2nd Biannual and Black Sea Scene EC project joint conference on climate change in the Black Sea ? hypothesis, observations, trends, scenarios and mitigation strategy for the ecosystem. 6-9 October 2008, Sofia, Bulgaria.

Kucheruk, N., 2006. Integrated study of eutrophication and biodiversity in the Russian coastal waters. Proceedings of The First Biannual Scientific Conference: Black Sea Ecosystem 2005 and Beyond, organized by Commission on the Protection of the Black Sea Against Pollution, May 2006, Istanbul.

Medinets, S. and Medinets, V. (2008) Results of investigations of atmospheric pollutants fluxes to the surface of Zmeiny Island in western part of the Black Sea in 2003-2007. In: 2nd Biannual and Black Sea Scene EC project joint conference on climate change in the Black Sea ? hypothesis, observations, trends, scenarios and mitigation strategy for the ecosystem. 6-9 October 2008, Sofia, Bulgaria.

?Moncheva, S. 2005. Phytoplankton shifts in the Black Sea ? Driving forces and implication for reference conditions. Proceedings of the JRC Workshop, 26-28 October, 2005-Istanbul.

Nesterova D. A. (1987) Some features of succession of phytoplankton in the northwestern Black Sea. Hydrobiologycheskyi. Zhurnal, 23(1), 16 ? 21.

Oguz, T., Deshpande, A. G. and Malanotte-Rizzoli, P. (2002) On the Role of Mesoscale Processes Controlling Biological Variability in the Black Sea: Inferrences From SeaWIFS-derived Surface Chlorophyll Field. Continental Shelf Research, 22, 1477-1492.

Rayner, N.A., Parker, D. E., Horton, E. B., Folland, C. K., Alexander, L. V., Rowell, D. P., Kent, E. C., Kaplan, A. (2003) Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108 (D14), 4407, doi:10.1029/2002JD002670.

TDA (2007) Black Sea Transboundary Diagnostic Analysis.

Temnykh, A., Melnikov, V., Zagorodnyaya, Y., Moryakova, V. (2006) The variability of the Black Sea zooplankton as a derivative of long term dynamics in the water hydrological structure. In: Proceedings of The First Biannual Scientific Conference: Black Sea Ecosystem 2005 and Beyond, May 8 2006, Istanbul, Turkey.

Yakushev, E., Kuznetsov, I., Podymov, O., and? Belokopytov, V (2008) On the role of Bosphorusin the formation of the Black Sea redoxlayer biogeochemical structure (model based estimating). In: 2nd Biannual and Black Sea Scene EC project joint conference on climate change in the Black Sea ? hypothesis, observations, trends, scenarios and mitigation strategy for the ecosystem. 6-9 October 2008, Sofia, Bulgaria.

Yunev, O., Shulman, G., Yuneva, T., Moncheva, S. (2008) Long-term changes of ecological quality rating (Q-value) of the Black Sea pelagic ecosystem. In: 2nd Biannual and Black Sea Scene EC project joint conference on climate change in the Black Sea ? hypothesis, observations, trends, scenarios and mitigation strategy for the ecosystem. 6-9 October 2008, Sofia, Bulgaria.



[2] Since 2003, the neighbouring population of common dolphins in the Mediterranean Sea is included as ?Endangered? (EN) in the IUCN Red List of Threatened Animals.

[3] Examples of non-market valuation techniques include expressed preference techniques such as contingent valuation, contingent ranking or discrete choice modeling and revealed preference methods such as the travel cost method, hedonic pricing and production function techniques. (Freeman, 1993).

[4] The concept referred to is the Environmental Kuznets Curve (EKC), which postulates an inverted U-shape governing the environmental performance of countries in relation to their per capita income (Dasgupta et al. 2002). The ?turning point? is typically in the range of incomes characterizing middle income countries, such as those in the Black Sea region.

[5] Exceptions include regulations governing aspects of fishing (e.g. mesh size, seasonal openings, etc.), but the enforceability and success of these measures is uncertain (Black Sea Commission, 2007).?

[6] A structural change approach was used to capture the shift between marine system regimes. Initially, the concentration of phosphates was set at 5.5 ?M, its average value in the northwest shelf of the Black Sea during the period. A second set of solution values was based upon a hypothetical 50% reduction in the phosphate level (to 2.75 ?M).

[7] Tourism data presented here is from the World Tourism organization website, http://www.unwto.org/facts/menu.html. Accessed December 17, 2007.

[8] Consumers? surplus represents is estimated as the difference between what one must pay for a good or service and what one would be willing to pay.

[9] Accessed on November 27, 2007 at www.worldbank.org.

[10] The World Bank website states that: ?An economic rent represents the excess return to a given factor of production. Rents are derived by taking the difference between world prices and the average unit extraction or harvest costs (including a 'normal' return on capital)?.