Land-based sources of pollution (including nutrients) alter pelagic and benthic habitats of more than one country, particularly in inland seas where water exchange with other seas and oceans is constrained. Coastal wetland habitats and communities have also been drastically modified as a result of upstream water abstraction and changes in the flooding regime.

Impacts on biodiversity extend far beyond national boundaries. A number of activities, processes, resource uses and practices across the Black Sea riparian countries impact the Black Sea, the consequences of which result in pressures on marine biodiversity, the most important of which are: eutrophication, unsustainable fishing/harvesting (overexploitation and destructive fishing practices), habitat destruction, invasive alien species and chemical pollution. Waste produced in the catchment areas disperses around the Black Sea via marine currents. Transboundary effects arise if the impacted habitats are nursery and spawning grounds for commercially important migratory fishes, marine mammals and birds.

Economic globalisation has also provided unprecedented opportunities for species to overcome geographic barriers and establish in new habitats. Enclosed or semi enclosed ecosystems, such as the Black Sea, seem particularly sensitive to biological invasions. With increased shipping traffic, aquaculture and trade the Black Sea has become a major recipient of alien species. The shared marine environment contributes to the spread of alien species from one national sector to the others. Alien species can cause irreversible environmental impact at the genetic, species and ecosystem levels in ways that cause significant damage to the goods and services provided by ecosystems and thus to human interests. For this reason, they are now recognized as one of the great biological threats to the environment and economic welfare globally.

Habitats of transboundary importance can be defined in a number of ways: (i) those shared by several countries; (ii) those which suffer change due to causes that originate in or are contributed by another country; and (iii) those which may or may not be localised in one country but internationally important feeding/breeding/spawning/nursery/wintering grounds for migratory organisms. Three particular habitat types have been identified as habitats of transboundary importance: (i) coastal margin ecotones; (ii) pelagic habitats; and (iii) benthic habitats. The environmental impacts and socio-economic consequences of habitat loss/degradation and community modification for each of these habitat types are described below.

Coastal margin ecotones

Due to human pressures, aquatic coastal habitats have undergone significant modification during recent decades. The following environmental impacts resulting from habitat loss/degradation have been documented: frequent and intense algal blooms, modification of community structure and changes in food webs, depletion of fish stocks, loss of migratory species using the habitat, as well as altered migration patterns, increased mortality of aquatic organisms and avian mortality, decreased native species diversity, increased proportion of threatened species, changes in ecosystem stability, alien species establishment and increased vulnerability to opportunistic invaders, ecosystem degradation.

The socio-economic consequences originating from habitat loss/degradation encompass reduced options for freshwater use, increased costs of alternative water supplies, increased costs of water treatment, loss in feral and cultured fisheries, reduced options for aquaculture development, loss of tourism, recreational and aesthetic value, loss of educational and scientific value, costs of clean-up and preventive measures, costs of restoration of modified ecosystems, loss of sanctuary and protected areas and associated wildlife.

Pelagic habitat

The major environmental impacts of pelagic habitat degradation include algal blooms, water quality impairment (reduced transparency, jelly and mucous accumulation, hypoxic events), modification of community structure and food webs (elimination of large top predators via fishing activities, predominance of small pelagic species exerting top-down control over the food web, dead ends in the food web as a result of jellyfish), alien species establishment and ecosystem instability.

Benthic habitats

Reduced ecosystem stability/resilience and a move towards nutrient enrichment and phytoplankton growth has had a dramatic effect on the bivalve community (e.g. the Mediterranean mussel, Mytilus galloprovincialis).. When the degraded bivalve community is unable to cope with food supplies from phytoplankton blooms and detritus, the excessive supply creates a huge oxygen demand leading to bottom hypoxia. Degradation of mussel beds which support diverse epifauna, infauna and interstitial community leads to decline/loss of species and genetic diversity. Habitat degradation is associated with decrease of food resource and breeding, spawning and nursery grounds for a range of commercially important species therefore the following socio-economic consequences arise: reduced capacity to meet basic human needs (food) for local populations, changes in employment opportunities, loss of existing income and foreign exchange from fisheries. Water quality impairment is linked to a decrease in recreational and aesthetic value with implications for tourism. Human conflicts arose on the issue of Rapana venosa fisheries. The scientific community was alarmed by the use of mobile bottom gears due to their detrimental effect on mussel beds and ultimately, ecosystem instability (Konsulova et al., 2003). On the other hand the socio-economic importance of the Rapana shellfishery in terms of processing and export has increased significantly during the last decade due to high external market demand and also the collapse of other commercial species stocks since the late 1980s. Clearly the problem is an issue which needs further research to assess the ecological impacts against the socio-economic benefits and suggest options for balancing the stakeholders’ interests.

Over the last few decades, the reduction of key species distribution and biomass has caused a subsequent decline in species richness, density and biomass of the associated fauna and flora. Community structure was modified due to sensitive brown algae (Cystoseira spp.) elimination and an increased development of tolerant red and green algae (Ceramium, Enteromorpha, Cladophora), and epiphytic algae. In the mid 1990s the expansion of the alien species Desmarestia viridis in Ukrainian waters further changed the community structure. Habitat decline resulted in reduced capacity for local populations to use Cystoseira as a source of alginates and animal feed or fertiliser. Furthermore, its potential use as a source of bioactive pharmaceutical products (sulfopolysaccharide, anti-inflammatory drugs) was impacted. A decline in aesthetic, recreational and educational/scientific value is also a noteworthy social loss.

The decline in eelgrass (Zostera spp.) beds has resulted in the loss of a habitat and food source for a number of associated species within the habitat and in surrounding benthic communities. A consequence of this has been an increase in coastal erosion by wave energy due to the loss of sediment stabilization by seagrass beds.

Among various sandy bottom inhabitants the bivalve Lentidium mediterraneum has suffered the most significant decline, especially along the NW coasts of the Black Sea (mainly Ukraine). The decline in the population of valuable commercial species such as the great sturgeon, the starred sturgeon and the turbot, is partially associated with the decline in Lentidium population, on which they feed. The consequence of this is a potential loss in earnings from fisheries and employment opportunities have been reduced.

Alien species introduction

The environmental and economic consequences of introduced species are considered generally unfavourable though beneficial effects may also occur. Nearly 10 % of the established alien species in the Black Sea and coastal aquatic habitats are considered to be highly invasive and another 16 % as moderately invasive. Highly invasive species are recognized to have a serious impact on biological diversity due to:

• Severe impacts on ecosystem structure and function (e.g. alteration of habitat, competing with native species, entering food chain, altering energy and nutrient flow etc.).
• Replacement of native species throughout a significant proportion of their range.
• Hybridization with native species.

Ultimately this has represented a significant threat to the unique biodiversity of the Black Sea. In addition to their impact on biodiversity invasive aliens also have negative consequences for human activities, including health and economic interests. They are often considered as pests, pathogens or vectors of disease, and cause declines in the populations of commercially important species either through competition or predation. Many also become nuisances through fouling hydraulic constructions, clogging waterways, reducing water quality, and reducing aesthetic and recreational value. Conversely, aliens may also integrate well in the receiver ecosystem and generate positive ecological effects as well as become valuable commercial resources. A brief overview of the impacts of selected invasive alien species in the Black Sea is given below.

Among 38 alien phytoplankton species, three are assessed as highly invasive: the diatom Pseudosolenia calcar-avis, the prymnesiophyte Phaeocystis pouchettii and the cryptogenic prasinophyte Mantoniella squamata. Several more are deemed moderately invasive. Algal blooms caused by the listed species have been associated with zoobenthos mortality, fish asphyxia, pelagic community change and food web disruption. Negative economic consequences derive from impaired water quality and decreased beach water aesthetics which imply losses in tourism.

Among the 33 alien zooplankton species two have become central to the Black Sea ecosystem in the last 2 decades: Mnemiopsis leidyi notorious for its detrimental effect on the pelagic food web and fisheries collapse; and Beroe ovata reputed to be assisting in the  restoration of ecological balance by reducing the former through selective predation on it. However, evidence to support this is mixed (see Section.3.3.2) Competition for food resources with planktivorous fish (e.g. sprat) and predation on fish larvae, together with overfishing resulted in the collapse of the pontic horse mackerel and anchovy fisheries during the late 1980s/early 1990s. M. leidyi was also indirectly responsible for enhanced harmful algal blooms in the 1980s. Furthermore, it reduced water quality due to mucous/jelly accumulation that caused visual pollution and hypoxia which impacted on coastal tourism.

The establishment of B. ovata in the Black Sea resulted in a decline in the M. leidyi population, an increase of plankton fauna diversity and mesozooplankton/fish larvae density and biomass. However, B. ovata has only narrowed the period of Mnemiopsis impact on the ecosystem, as it is prone to strong seasonal and interannual fluctuations (Vinogradov et al., 2000). Consequently when it is not present during the summer period, M. leidyi flourishes (Shiganova et al. 2001; Kamburska et al., 2003a,b; Kamburska, 2004).

Alien zoobenthos comprise 63 species, which arguably makes this ecological group the most successful colonizer in the Black Sea. For example, the Janapanes snail Rapana venosa is a habitat generalist and exploits practically every available prey. It has occupied an empty ecological niche in the Black Sea and has exerted significant predatory pressure on the indigenous malacofauna. The impact on bivalve populations is variable and ranges from rather mild along the Romanian coast possibly due to suboptimal environmental condition, moderate in Bulgarian and Turkish Black Sea, and severe along Russian and Ukrainian coasts, where the whelk has been blamed for local exterminations or major declines in the numbers of other bivalves. R. venosa is well established in the benthic ecosystem of the Bulgarian, Romanian and Turkish Black Sea and has become a commercially valuable living resource. Demand for Rapana meat on the international market increased the commercial value of this resource initially withinin Turkey (1980s) and then in Bulgaria (1990s). In Romania, medium-large scale ‘subsistence’ harvesting is likely to develop into an export-oriented industrial-scale enterprise in future years. In Ukraine R. venosa usesare limited to local subsistence fishery and souvenir manufacture/trade.

Positive economic effects from R. venosa fishery are counteracted by negative ecological side-effects of destructive fishing practices used in Turkey and Bulgaria where R. venosa is fished with dredges and beam trawls, in the latter country illegaly. In contrast, in Romania R. venosa is selectively fished by SCUBA divers, a sustainable method which does not disturb the habitat or involve by-catches of other animals. However, signs of over-harvesting are already evident in some areas. A new, sustainable,  method of harvesting Rapana is currently being trialled in Turkey, with promising results. This uses baited traps, analagous to lobster/crab pots, which offer no harm to benthic habitats, with minimal by-catches and greater control over the size/age of Rapana caught.

Other examples of alien zoobenthos include:

• The clam Anadara inaequivalvis, a habitat generalist, highly tolerant of hypoxia, long lived, with high reproductive output and having the capacity to develop massive populations where environmental conditions are optimal.
• The acorn barnacle Balanus improvisus which increases the self-clearing capacity of shallow hard-bottom habitats and can form nuisance fouling on underwater constructions.
• The Chinese mitten crab Eriocheir sinensis a benthic predator which causes considerable erosion to mud/sand banks through burrowing.

A total of 27 aquatic/semi-aquatic alien vascular plants have been identified in Black Sea wetland and coastal environments. Three are characterised as highly invasive, another 5 - as moderately invasive. For example, Nuttall’s pondweed Elodea nuttallii grows in dense thickets, attached to the bottom of lakes and slow-flowing rivers and canals and can impede water flow and navigation. At present the species is spreading in the Danube Delta, Danube floodplain and major tributaries of the Danube.

Biodiversity changes in the Black Sea are closely linked to each of the other identified transboundary problems. Eutrophication is recognized among the primary causes of Black Sea marine and coastal habitats degradation. Phytoplankton blooms are associated with the decline in species/habitats sensitive to increased turbidity (light attenuation), smothering and hypoxia. (Section 4.2).

Fisheries exert significant pressure and cause the decline in abundance/biomass/stocks not only of target commercial fishes but also of non-target by-catch species, including fishes, mammals and birds. Destructive fishing practices such as the use of mobile bottom gears contribute to habitat degradation by causing physical disturbance, mortality, smothering of habitats by suspended sediments and discards. (Refer to section 4.3)

The immediate, underlying and root causes of biodiversity change/habitat loss are shown in the causal chain analysis presented in Fig. 4.19. However, this analysis is expanded upon in Section 4.5.4.1 by considering the causes of biodiversity change in terms of major habitat types. In Section 4.5.4.2, vectors of alien species introduction (a primary cause of biodiversity change) are discussed in detail and threats to endangered “red list” species are covered in Section 4.5.4.3. Further detail on the immediate causes of biodiversity change/habitat loss can also be found in Sections 4.2, 4.3, 4.4, all of which are drivers of this transboundary problem.

Habitat loss/degradation

Benthic habitats

Vectors of alien species introduction

The analysis of introduction vectors shows that the majority (68 %) of the introductions are human-mediated and only 13 % are a result of the natural expansion of species (Figure 4.20). A considerable portion of the aliens have no known vector (see Annex 6). However their native range excludes the option of natural expansion, therefore anthropogenic vectors are assumed as well. Among human-mediated dispersal mechanisms ships are clearly identified as the primary vector (30 %) of alien introductions in the Black Sea, followed by aquaculture (11 %). Figure 4.20 Vectors of alien species introductions in the Black Sea and coastal aquatic habitats

Major threats to IUCN red list species

Pollution, habitat destruction, exploitation (overfishing) and disturbance are recognized as important threats in all Black Sea countries (Fig. 4.21). Eutrophication is almost certainly underestimated as a threat factor, due to a misunderstanding of categories by national experts. Many entries which should have gone under eutrophication were probably listed as agriculture and pollution. The prevalence of disturbance (due to tourism, trampling and military activity) predominantly affects waterfowl and shorebirds of the Black Sea wetlands. As birds are the most thoroughly assessed systematic group in the region, they comprise a large share of the threatened species list and hence the influence on the ranking of threat factors. Climate change is clearly not recognized as threat factor and is not assessed properly in most Black Sea countries, although it is one of the major drivers behind biodiversity change in the Black Sea at present. Parasitization and displacement by alien species is either largely overestimated, as it is the case in Ukraine and Georgia, or not considered at all, as in Turkey. These inaccuracies/misinterpretations are reflected in the overall picture of threat factors in the Black Sea, where eutrophication is obviously underestimated as a threat, while minor factors like parasitisation and displacement by alien species, agriculture and forestry are overestimated (Fig. 4.22).   Figure 4.21. Factors of threat to red list species in each of the Black Sea countries Figure 4.22 Overall picture of threat factors to Red List species in the Black Sea (legend abbreviations as in Figure 4.22)

The underlying socio-economic drivers of the unsustainable practices and resource uses that cause biodiversity change in the Black Sea encompass legal and institutional incapacity in a number of sectors:

• Agriculture: lack and/or poor enforcement of environmental protection regulations in agriculture, diminished government control of privatized farms, lack and/or poor planning of agricultural land use, low awareness of negative environmental effects.
• Industry: lack and/or poor enforcement of environmental protection regulations in industry (including energy and exaction of raw materials), poor or no enforcement of trade waste discharge regulations, weak industrial policy and related legislations, no incentive for pollution prevention and control.
• Transport: lack and/or poor enforcement of environmental protection regulations in shipping and harbours, no incentive for pollution prevention/ control.
• Fisheries: lack of Black Sea fisheries international agreements/ regulations, lack and/or poor enforcement of national fisheries management and control plans, no effective control of fishing practices.
• Urbanization: uncontrolled development in coastal areas, low level of user fees (tariffs) and incentives for water use and treatment, poor management and/or poor capital investment and operational funding for waste water collecting/treatment system.
• Tourism: unsustainable tourism practices, lack and/or poor enforcement of environmental protection regulations in tourism.
• “Hard” civil engineering approach to flood defence/hydroelectricity/shipping/ coastal erosion issues.
• Lack and/or mismanagement of public funds dedicated to improve the quality of the environment.

For more details on these underlying socio-economic drivers, refer to Sections 3.2, 4.2, 4.3 and 4.4.

Knowledge gaps differ among Black Sea countries depending on the variable national research effort. Georgia was identified as having most serious gaps of information regarding national habitats, threatened species and alien species. Russia did not provide any of the requested data on biodiversity change, which impeded the regional assessment.

Generally, data deficiency or knowledge gaps are recognized in the following:

• Changes in the spatial extent of habitats are largely unidentified. Habitat fragmentation is not assessed, changes over time are unknown.
• Lack of long term data sets and temporal and spatial patchiness of data on most of the quantitative indicators to assess diversity change.
• Vectors of introduction are unknown for a large number of aliens, a great deal of speculation and assumption may lead/have led to the development of weak management strategies and continue to leave invasion windows open.
• The level of threat to species according to IUCN categories and criteria is evaluated for a limited number of species. Re-evaluations at regular intervals are absent to provide assessment of the change in the level of threat over time.

The structure of marine ecosystems in the Black Sea differs from that of the neighbouring Mediterranean Sea in that species variety is lower and the dominant groups are different. However, the abundance, total biomass and productivity are much higher than in the Mediterranean Sea. Plankton community composition and biomass suggest that improvements are taking place, albeit that a reduction in organic enrichment is key to this recovery.

Changes in aquatic coastal habitats vary and are dependant on the intensity of environmental pressures at the sub-regional level. The Danube Delta and the Bulgarian coastal wetlands probably continue to experience diversity decline and impaired ecological status compared to the 1960s, despite the considerable reduction in habitat degradation due to the designation of extensive protected areas and the implementation of management plans aimed at biodiversity and water quality restoration. The Dnipro Delta and the Turkish coastal aquatic habitats have continued to decline due to eutrophication and pollution.

Changes in the pelagic ecosystem towards the end of the 1990s reflects healthier conditions, especially in the Formerly “dead” areas of the NW Shelf, where decreased nutrient loads were coupled with favourable climatic change. However, the once massive area dominated by Zernov’s Phyllophora (a red seaweed) field has decreased hugely in area, having been replaced by other, opportunistic macroalgae. Similarly, during the last two decades, the area covered by eelgrass (Zostera) has decreased tenfold in shallow waters. Despite the signs of recovery (rise of zooplankton and small pelagic fish stocks) the habitat shows a state of ecological instability, as well as sustained significant stock decline of large pelagic fish species. The Turkish Black Sea area is in a poor ecological state and biodiversity has decreased during the last decade, as in other areas of the Sea. Environmental and biodiversity changes in the SE Black Sea area remain unclear either due to insufficient research (Georgia,) or a lack of data ptovision (Russia).

The invasion of Mnemiopsis leidyi contributed to a catostrophic decline in fish productivity in the late 1980s/early 1990s. The subsequent invasion of a another comb jelly (Beroe ovata), which feeds on the original invader, means that opinions are now split as to whether Mnemiopsis istill has a major impact on fish communıtıes and catches.

The number of registered alien species at the regional level amounts to 217 (parasites and mycelium excluded). Nearly half of them (102) are permanently established, a quarter - highly or moderately invasive (20 and 35 species respectively). This high ratio of invasive aliens suggests a serious impact on the Black Sea native biological diversity, with negative consequences for human activities and economic interests. Furthermore it is unlikely that it will possible to revert to the ecological conditions of the 1960s, due to the practicalities of eradicating introduced alien species.

Habitat status is a critical component of maintaining high levels of biodiversity within the Black Sea. All 5 habitats within the coastal margin ecotones category are considered to be in a critical status in at least one country; both types of benthic pelagic habitat (neritic and open sea) are considered critical in at least one country; and 13 of the 37 types of benthic habitat are considered to be critical in at least one country. No data were available on Russian Black Sea habitats. The ecosystem(s) of the Black Sea are, therefore, seriously damaged and in need of legal protection. Those habitats most at risk include the neritic water column, coastal lagoons, estuaries/deltas and wetlands/saltmarshes.

The following recommendations are suggested in order to respond to the issue of biodiversity change in the Black Sea:

• Continue capacity-building and training of marıne scientists.
• Allow environmentalists greater access to key decision-makers in organisations throughout the Black Sea region.
• Undertake regular re-evaluations of major marine systematic (biological) groups in each of the BS countries, using the latest IUCN criteria and guidelines for application at the regional level.
• Develop a habitat- and ecosystem- oriented approach to biodiversity management. Often it is clearer which impacts are responsible for the deterioration of habitats than it is for individual species .
• Once national Red Lists on habitats and biota have been completed, a Red Book of Habitats, Flora and Fauna of the Black Sea should be created. This should serve as a tool for conservation management at the regional level.
• Increase the number and area of Marine Protected Areas.
• Improve and back-up management strategies to prevent the introduction of new invasive species. These should target the priority vectors of introduction – ships (ballast water) and aquaculture.
• Develop a monitoring system for the early detection of alien species, especially in “hot-spots” – ports, aquaculture areas.
• Promote the International Convention for the Control and Management of Ship’s Ballast Water and Sediment and develop a Black Sea “Action plan” on ballast water management.
• Improve the egulation and control aquaculture of alien species.
• Develop and implement a plan for the Protection and Recovery of Black Sea Cetaceans in close cooperation with ACCOBAMS.
• In cooperation with fisheries sector establish biological safety limits for commercial exploitation of marine living resources (see Section 4.3.7).
• Develop options to decrease the inputs of nutrients and chemical pollutants (detailed options are described in Sections 4.2.7 and 4.4.7).