Aquatic Ecosystems of the Aegean and Black Sea Basins

Yordan Uzunov, Stanoy Kovachev, Krassimir Kumanski, Jenny Ludskanova-Nikolova

Summary

This report deals with the biological diversity of the aquatic ecosystems in the Aegean and Black Sea basins. For each river basin - including the running waters, standing waters, and groundwater - biological diversity is discussed at three levels: species, cenotic (community), and ecosystem. The main sources of information were academic scientific journals and other publications, as well as several additional sources, such as the BIOMONITOR Information System. The bibliography contains a total of 334 titles of background papers.

In this century, there have been three main approaches to the study of the biodiversity of aquatic ecosystems - faunistic, cenotic, and applied. These approaches have been grounded in their main subject area, rather than in the time period per se.

The total aquatic invertebrate species richness in the watersheds under review was determined to be 2240 species and subspecies from 49 systematic groups. The number of recorded species tended to reflect the size of the river basins. Thus, the total number of species recorded for the largest river basin, that of the Maritsa (watershed area of 21,100 km2) was 1263, as opposed to 275 species for the basin of the Veleka River (995 km2). These figures were based on analyses of cenotic and habitat/ecosystem diversity within selected river basins.

The inclusion of coastal water bodies in this review essentially diversified the list of species present by bringing in numerous oligo- and/or euryhaline representatives. Several groups, however, seemed to be insufficiently studied in accordance with the Limnofauna Europea when compared with the situation in neighboring countries.

The level of rarity among the species present was discussed in the context of the environmental health of the habitats/ecosystems. Emphasis is placed on the high level of endemism within phreatic (groundwater) habitats, in contrast with the surface waters, both running and standing, which were affected to a much greater degree by human activities.

Concerning cenotic diversity, there was found to be a discrepancy in the levels of exploration of the various communities within the provinces under review. Thus 1153 species were established for natural rivers and streams, but only 8 for artificial channels. The main information about standing water bodies, both natural and man-made, concerned the zooplankton community rather than the zoobenthos. Data on meyobenthos, periphyton, and other communities was insufficient or totally lacking.

Ecosystem diversity was insufficiently studied with respect to various habitat types, especially those of human origin (e.g., rice fields, fish ponds, smaller reservoirs, and cooling basins). The unique properties and high fragility of the coastal and glacial lakes, among the ecosystems under review, are also emphasized. Some regions of special importance along the Black Sea coast and in the high mountains are outlined.

The real and potential threats and dangers to biodiversity in the aquatic environments of the provinces under review include different types of water pollution, hydrotechnical constructions, global climatic changes, and the trans-boundary/regional transport of pollutants by means of atmospheric processes. These threats are discussed in detail.

It can be concluded that species diversity within both the watersheds under review was well studied, in contrast to cenotic and ecosystem diversity. Although up-to-date information is lacking in certain areas, there are no poorly known river basins (i.e., "blank spots") requiring initial studies of their biodiversity. Nevertheless, many ecosystems require inventory of their species and cenotic diversity, especially with respect to the on-going processes of environmental changes resulting from human activities. Several paradoxes are described in assessing our knowledge of the biodiversity of the aquatic ecosystems of the Black Sea and Aegean watersheds.

Introduction

Several basic principles have been followed in developing this report on the biological diversity of the Bulgaria's freshwater ecosystems.

The basin (or watershed) approach was adopted as a basic organizing principle at two levels. The first includes the catchment areas of both the Aegean and Black Seas. The second takes in individual river basins, including the rivers, lakes (both natural and artificial), and groundwaters. The divisions of the main basins followed that used in the National Monitoring Network codification of the Ministry of Environment (MOE) (See Appendix 1). Several smaller rivers in the Black Sea province that lacked their own code were placed into a single group. Some brackish and hyperhaline coastal water bodies without outflow were also included in this group since they are fed by fresh groundwater flow.

The biological diversity of the different basins was discussed at three levels:

By mutual agreement among the participants in the National Biological Diversity Conservation Strategy workshop, the "green" components of the ecosystems (phyto-plankton, periphyton, and vascular plants) are discussed in other reports prepared by the botanists. Similarly, the insect fauna are reviewed separately in the reports on terrestrial invertebrate fauna. Data regarding larval stages and several amphibious insects are only summarized here. Thus, this report mainly concerns the primarily aquatic invertebrate fauna.

The basic resources for information were academic publications, from both Bulgaria and other countries, such as scientific journals, special publications, monographs, and so forth. The reports and proceedings of congresses, conferences, symposia, and other scientific meetings were intentionally avoided on the presumption that the most important information had already been published in respected scientific journals. Unpublished data, expert consultations, and annual reports (such as those commissioned by the MOE) were also used, but are not listed in the bibliography. An additional important source was the data base of the BIOMONITOR Information System which has been developed and maintained by the author and collaborators since 1987. This system provides data on species richness and diversity, and on the water biological sufficiency (wbs) and quality of the rivers. It includes information from over 400 monitoring sites, as assessed by standardized methods using biotic and cenotic indices/parameters of the macro-zoobenthic community.

More than 330 articles are listed in the bibliography. It is the personal judgement of the authors that this represents about 75% of the definitive contributions in this field. Most of the entries (254) refer to articles found in 18 Bul-garian journals, while 80 titles were published in 43 international or foreign journals. At present, a total of 58 Bulgarian authors have published 285 articles (243 within Bulgaria and 42 abroad), while 34 foreign authors have contributed 49 articles (11 in Bulgarian journals, and 38 in foreign journals).

Historical Background

Three basic periods or directions can be identified in the history of research on the biodiversity of freshwater and brackish water ecosystems. These periods are linked together, and it is quite difficult to separate them in time. Each is well grounded in its main area of focus (see Table 1).

The "Faunistic Period" began at the start of the current century, and has continued up to the present. It has focused on providing data about species richness and the location and distribution of aquatic fauna by means of taxonomic, systematic, caryological, and other specific methods. The approach in these studies has been largely determined by systematic groups and units, rather than the typology of communities or ecosystems. Intensive faunistic studies have been carried out over the last 30 years in several regions of Bulgaria, including the Thracian lowland (BAS, 1964, 1965, 1966), the Black Sea coastal lakes and estuaries (BAS, 1967), the Rhodope Mountains (BAS, 1975), and the lower part of the Strouma River (BAS, 1990). After the publication of several faunistic catalogues (e.g., Valkanov, 1954; Valkanov and Marinov, 1959; Svetkov and Marinov, 1986; Naidenov, 1986, 1988; Marinov and Golemanski, 1989), prominent summaries of the studied groups appeared in the issues of the Fauna Bulgarica. At present, there are 4 volumes concerning species richness and diversity of the groups Polychaeta (Marinov, 1977), Trichoptera (Kumanski, 1985b, 1988), and Coleoptera: Hydracanthares (Guerguiev, 1987) in Bulgaria.

The "Cenotic Period" has developed parallel to faunistic period, especially over the last twenty years. The main subject of research in this area is the variety and abundance of specific species assemblages and communities in various kinds of habitats and ecosystems, both natural and man-made. These studies have focused on the dynamics of quantified community parameters that reflect environmental factors, including those of human origin (e.g., water pollution, eutrophication, hydrotechnical constructions). The numerous contributions in this area have provided information about the dynamics of species composition, density, biomass, productivity, and structural organization, and the ecological/ environmental tolerances of the zoobenthos, zooplankton, periphyton, and phreatic fauna as living components of running, standing, and underground water bodies.

The "Applied Period" has arisen in the last twenty years, but it is based on work in the previous periods and other areas of focus. These studies focus on ecological assessment of the state of the environment and the health of the processes within aquatic ecosystems, based on knowledge about biological/species diversity, ecological tolerances, and specific features of the respective organisms and communities. Two "sub-directions" can be identified. The first has addressed problems of productivity, or, in general, trophic potential and capacity, mainly of standing water bodies (both natural and artificial) by studying the zooplankton and zoobenthos communities. The second examines water quality and assesses environmental impacts, mainly in running and underground waters, through bioindication and structural analysis, using the river macrozoobenthos and phreatic fauna. Thus, this period has provided many contributions to the assessment and management of water quality, fish productivity, self-purification processes, and so forth.

Current State of Knowledge

For many reasons, we can regard our knowledge of biological diversity within the aquatic ecosystems of the Black Sea and Aegean catchment area as well advanced. Many of the systematic groups have been completely elaborated, and it is unlikely that new faunistic discoveries will be made. The main types of communities and ecosystems have also been well studied. There are few if any regions where biological diversity has not been studied to some degree. Furthermore, much of the research has concentrated on regions and objects of special zoogeographical, economic, and/or environmental interest. It has thus been possible to conclude that the biological diversity of both the Aegean and Black Sea provinces is sufficiently studied.

At the same time, however, there have been and still are well-founded doubts about the validity of these conclusions due to several unresolved paradoxes. In general, they reflect problems with the temporal and spatial scaling of our knowledge of biodiversity in the aquatic ecosystems in these provinces.

The paradox of the cumulative number of entries in the faunistic lists originates in the practice of adding every newly found species to the historical list. No system of long-term monitoring has been in place to ensure that a given species in the fauna, especially those included at an early point, are truly present. Thus, species diversity may seem greater than it actually is.

The paradox of data incompatibility originates in the practical impossibility of studying simultaneously and entirely all systematic groups, communities, and/or ecosystems. Many changes, sometimes radical, can happen in the environment and in the biota between periods of investigation. Thus, comparisons between any two objects or places must take into account the time factor.

The paradox of discrete knowledge originates in the fact that biological diversity has been studied group-by-group or object-by-object. Consequently, there has been much data about particular groups or objects, but little or no data for all groups of species and all objects under investigation. Thus, the mental picture of biological diversity has been limited, and perhaps even invalid, in each concrete case.

The paradox of ecological ignorance originates in the neglect of environmental changes due to human activities both past and present. There have been numerous and essential alterations in the general ecological situation, so that many habitats and aquatic ecosystems no longer exist, or living conditions have so shifted that there is no reason to expect further findings of numerous species, especially of sensitive, rare, or endemic species. But many species from these areas are still found in the lists of the Bulgarian limnofauna. Thus, the depiction of biological diversity in the aquatic ecosystems of the provinces under review seems to be approximate rather than definitive.

For these reasons, discussions of the distribution of species have been based strictly on published facts, rather than on an accurate understanding of their actual or potential distribution.

Species Diversity and Richness

The total number of recorded species and lower taxa within the range of the areas reviewed was determined to be 2240 (Table 2). A margin of error of about +/- 20% should be assumed due to the lack of long-term taxonomic reviews, the new faunistic contributions, and/or the presence of newly described species. This percentage was calculated on the basis of the average proportion of invalid names (synonyms, species of dubious taxonomic status, newly revised or "lumped" species, etc.) for several sufficiently elaborated groups of hydrobionts.

For example, up to the present 136 species names have been recorded for aquatic Oligochaeta from riverine and lacustrine macrozoobenthos in Bulgaria. After updating their taxonomic status and distribution, only 106 species (46 genera from 8 families) were actually represented in the species list of the Bulgarian limnofauna (after Uzunov and Kapustina, in press). Two hundred and thirty-eight species of caddisfly (Trichoptera), including 2 subspecies, are now established for Bulgaria; recently, however, 207 names that were used in the past have been shown to be invalid (after Kumaniski, 1985b, 1988). Among the aquatic beetles (Coleoptera: Hydracanthares), 30 species names are no longer used in descriptions of the 139 species established for the Bulgarian limnofauna (after Guerguiev, 1987).

Within the total species list, the relative proportions of the different systematic groups varied. The groups most represented seemed to be Protozoa (15.5% of the total number of recorded species), larvae of the insects from the Diptera: Chironomidae (9%), Trichoptera (7.6%), Coleoptera (6.6%), Copepoda (8.2%), rotifers (7.3%), etc.

Because brackish and hyperhaline coastal lakes and the estuarine portions of the Black Sea tributaries were taken into account in this review, the list was essentially diversified through the inclusion of marine and brackish representatives. Thus, all the recorded species from Phlyllopoda, Branchiopoda, Cirripedia, Anizopoda, and many representatives from Hydrozoa, Turbellaria, Nemertini, Polychaeta, Gastropoda, Bivalvia, Amphipoda, Isopoda, and other groups, were oligo- or euryhaline hydrobionts.

In comparing data from the Bulgarian literature with the information in the Limnofauna Europaea, some groups - Nematoda, Rotatoria, Gastrotricha, Tardigrada, many Diptera families, etc.- seemed to be practically unknown; their presence in neighboring countries indicates that they are probably more abundant in the Bulgarian aquatic fauna. Due to the shortage or absence of specialists able to delineate the whole range of the systematic group, there is insufficient knowledge about many inhabitants of both running and standing waters.

Species diversity in the river basins under study seemed to be highest in the larger basins: those of the Maritsa (1263 recorded species from 40 systematic groups), the Tundzha (662/35), and the Arda (604/31) (Table 2). This could be interpreted as a reflection of the greater number and types of habitats and ecosystems along the vertical gradient from high mountains to the lowlands. There was almost a direct correlation between the number of recorded species and the surface area of the river basins under review (Figure 1).

Rare Species

The topic of rare species should be discussed based on analysis that takes into account their dependence on specific habitats, their frequency, their density, and other characteristics. Several species from the European Red Data List (Appendix 3), including H. medicinalis (Hirudinea), A. astacus (Crustacea: Decapoda), G. flavipes, and O. cecilia (Odonata), were common in the basins under study. Their populations have not yet been damaged, in contrast to those of S. nitida (Gastropoda) and U. crassus (Bivalvia), for which this is no recent evidence of their actual existence in the zoobenthos due to environmental changes in the localities where they were last recorded.

Endemism

The level of endemism among the hydrobionts of open water bodies (both running and standing) was, in general, lower than that of the phreatic fauna (see Appendix 4). Most of those included in the list are representatives of the fauna of underground waters (e.g., caves, springs, wells). There are only a few exceptions (e.g., G. shablensis, H. thracicus). Within the Bulgarian phreatic fauna, relatively high levels of endemism were established for Gastropoda (73% endemics), Ostracoda (37%), Copepoda: Cyclopoida (36.8%) and Harpacticoida (42.8%), Syncarida (71%), Isopoda: Asellota (75%), and Hydracarina (14.3%). (Information about endemism among the insect orders is presented within the relevant reports by mutual agreement of the authors.)

A great portion of the phreatic Bulgarian and Balkan endemics are also relict forms. In addition, there are two main groups of relicts: Pontic-caspian relicts, which are distributed mainly in the coastal brackish water bodies (lakes and estuaries), and glacial relicts in the high mountains lakes (Appendix 5).

Gaps in Knowledge

The data in Table 2 are sufficient to conclude that the level of exploration of the river basins under review was relatively satisfactory. There is no reason to think that wholly unknown territories exist within the two provinces.

There is, however, a problem involving the proper correlation between the level of exploration of the various systematic groups and the various types of habitats/ecosystems. It can be seen in Table 3, for example, that among running-water habitats, 1153 species were established for natural rivers and streams, but only 8 for artificial channels. Sufficient information is lacking for several types of man-made water bodies (rice-fields, cooling reservoirs, deposition basins), for all types of temporary water bodies, for the waters of caves, and so forth.

Table 4 provides data concerning the level of exploration of species diversity in various habitats within the river basins under review. It should, of course, be remembered that the brackish and/or hyperhaline lakes occur only along the Black Sea coast, and the glacial lakes only in the high mountains of the Aegean catchment area. Nevertheless, a comparison of the number of recorded species seems to indicate that the dam lakes (reservoirs) of the Black Sea basin have not been sufficiently investigated. Other insufficiently studied groups and habitats include the riverine hydrobionts, native lowland lakes, and underground aquatic fauna.

Because the degree of study of species diversity within individual river basins was uneven, the conclusions about the current state of knowledge of biodiversity at the watershed scale should be considered approximate. For example, studies of the standing water bodies within the largest river basin (the Maritsa) contain published data on only several reservoirs (Batak, Pzhasatchnik, Rozov kladenets) and fish-ponds near the town of Plovdiv (after Dimitrov, 1960b, 1962, 1967, 1969b; Lyudskanova, 1967, 1969b, 1972b, 1975; Naidenov, 1964a, 1964b; etc.). There are no data for such large reservoirs as Belmeken, Topolnitsa, Domlyan, Trakiets, and Tserkoski, or for many of the smaller artificial water bodies.

The lack of data about species diversity within the full range of aquatic habitats is compounded by the lack of professionals sufficiently qualified to research the entire spectrum of hydrobiont taxonomic groups.

Cenotic Diversity

In contrast to the large body of information about species diversity, there is little data on the diversity of specific species assemblages or communities within the river basins under review. There is much information about riverine macrozoobenthos, but little about the lacustrine. The basic data about standing water bodies (both natural and man-made) concerns the zooplankton community and, to a much lesser degree, the benthic community. Except for one study of the Ropotamo River (after Svetkov and Gruncharova, 1976; Gruncharova, 1977), no further investigations of the periphyton community in the country have been conducted. Little data has been published about the meyobenthos or hyporeic communities as a whole. A general conclusion can thus be drawn that cenotic diversity has not been so well studied as has species diversity.

Ecosystem Diversity

In preparing this report, it was difficult to review the entire diversity of ecosystem types and, especially, the habitats they contain. For this reason, only those for which some published information exists have been emphasized. The number of recorded species as presented in Table 4 provides data about the level or degree of analysis for the different ecosystems (both natural and artificial) in the watersheds under review. It is evident that species diversity of entire groups of ecosystems/habitats are insufficiently known.

The coastal brackish and hyperhaline water bodies, as well as the estuaries of the Black Sea tributaries, are considered unique habitats/ecosystems due to the high species diversity of the communities they contain. Unfortunately, there is no recently published information about larger lakes such as Durankulak, Shabla, Varna-Beloslav, Vaya, and Mandra. The hydrobiological characteristics of several smaller coastal lakes and wetlands - Shabla, Tauk-Liman, Tuzla, Stamoplo, Arcutino, Alepu, etc. - have not been studied for decades. Meanwhile, environmental changes due to human activities have strongly damaged their biological diversity.

For example, the biota of the largest coastal lake - Varna-Beloslav - was studied in the 1930s (Valkanov, 1934, 1936) and later in 1964-1966 (Beshovski, 1964; Marinov, 1966; Kaneva-Abadjieva and Marinov 1967; Kaneva-Abadjieva, 1972). In the years that followed, the lake was completely transformed by a channel with a large harbor for ocean liners and merchant ships. Many industrial enterprises, mainly chemical and power plants, were built around its shore. As a consequence of these numerous and profound anthropogenic transformations in the lake, there is no further reason to regard it as a natural water body. To cite one particular effect, the population of Astacus leptodactylis - the main invertebrate hydrobiont of economic interest - has been fully destroyed. As concerns species and cenotic diversity, there exist only a few unpublished studies of the effects of pollution from the tributary Provadizhska River on the dynamics of the zooplankton community.

Many of the lakes and estuaries listed above are associated with wetlands of national and international importance. They lie along the Via Pontica, and serve as migratory stopover points and wintering locations for waterfowl and other birds.

Real and Potential Threats to Biodiversity

The many human activities that could or do present real threats to the biological diversity within Bulgaria's aquatic ecosystems are summarized here.

Pollution

Pollution, from both point and non-point sources, constitutes one of the most serious dangers to the species diversity of aquatic ecosystems. Furthermore, the changes in cenotic diversity, up to and including the complete elimination of certain communities, alter the functions, and hence the stability, of ecosystems.

The effects of pollution depend directly on the type and extent of the pollutants. Pollutants can be divided into several categories.

1. Saprogenic pollution

Loading with biodegradable organic matter, or saprogenic pollution, causes alterations in species composition. The more sensitive species are replaced by more tolerant species in all communities, while the species structure in general is simplified. In lotic systems, the relative share of zoobenthos and periphyton in the cenoses increases. In lentic systems, the zooplankton also increase. The deposition of organic matter in standing water bodies can, in some cases, cause the zoobenthos to be eliminated. Increasing eutrophication, and thus secondary saprobization, are the main features of aquatic ecosystems that are receiving high levels of biodegradable organic matter.

The Mesta River provides a well studied example. The Mesta was heavily affected by organic pollutants of industrial origin (mainly tarboard-paper and yeast production). More than 200 invertebrate taxa had been recorded for the zoobenthos. Changes consequently occurred in both species composition and the structure of the bottom community. The dominant tubificid species (Oligochaeta), for instance, changed as follows: Rhyacodrilus coccineus dominated upstream the source of the pollution, while Tubifex tubifex, Pasmmoryctides albicola and Psammoryctides barbatus dominated at three sites downstream of the source). The mean number of species was more or less equal (24-28 per m2), but the Shannon-Weaver index of species diversity varied between 3.353 for the first (unpolluted) site and 2.663 for the most affected site. After the pollution was eliminated, species diversity was restored (after Kovachev, 1977, 1984; Kovachev and Uzunov, 1986; Uzunov and Zhelezarov, in press; Uzunov and Molle, in press; Kovachev and Uzunov, unpub. data).

2. Inert pollution

Loading with suspended materials, or inert pollution, affects both the composition of the community and species richness. The species structure of the communities becomes rather distorted. In cases where the damage from suspended materials is strong, periphyton (in lotic systems) might be eliminated, while in lentic systems the zooplankton might be inhibited. Deposition and the elimination of suspended materials could stimulate the bottom-dwelling benthos and the zooplankton.

The Strouma River is an example of a stream that was heavily polluted by suspended materials of industrial origin (coal, cement powder, etc.). At sites immediately below the sources of the pollutants, the mean number of species present in the macrozoobenthos was less than 15% that of upstream sites. Two hundred and ten kilometers down-stream, the mean number of species was still only half that of the upstream sites, despite the fact that the level of the suspended materials had fallen more than 95%. After the inert pollutants were eliminated (1974-1975), the processes of recovery led to an increase in species richness, the number of known species in the river rising to 263, as compared to 132 for the previous, heavily polluted period (after Kovachev and Uzunov, 1977; Kovachev et al., 1979; Islam et al. 1985; Uzunov and Kovachev, 1987).

3. Toxic pollution

Loading with toxic materials, or toxic pollution, involves substances of various type and origin - heavy metals, oil products, organic substances such as pesticides, detergents, and antibiotics, etc. - and can damage biodiversity profoundly. The acute impacts can include the complete elimination of aquatic biota, while chronic impacts can include essential damage to populations and species. Communities can be destroyed or their structural organization distorted, as only a very few tolerant species are able to survive.

The upper stretch of the Arda River was among the many water bodies affected by toxic pollution, receiving heavy metals from the mining and processing enterprises in the region. No zoobenthos or periphyton were found for years along a 60-kilometer stretch of river downstream from the sources of the pollution. After these sources were eliminated (1990), the river entered the initial stages of recovery and the macrozoobenthos began to reestablish themselves (after Russev, 1959, 1964; Kovachev and Uzunov, unpub.; Uzunov, unpub.).

4. Thermal pollution

The heating of waters, or thermal pollution, is an example of a threat to the aquatic biota that is not well studied in this country. Several foreign studies have demonstrated the effects of alterations in water temperature on species composition in the communities, as the most sensitive species are replaced by the most tolerant or eurythermic species. An important aspect of thermal pollution is its intensifying effect on cenotic processes. The reproductive capacity of various populations is exhausted due to rapid turnover and alterations in life stages.

5. Mixed pollution

Aquatic organisms and systems are commonly exposed to various combinations of pollutants, or mixed pollution. Depending on the mix, species composition, species richness, and community structure can vary with sensitivity along the route of the affected river. As a rule, species diversity is lower than at sites that are free of impacts. Mixed pollution can permanently affect aquatic communities by exhausting their adaptive capacity and so transforming the biota.

The Maritsa River provides an example of the effects of mixed pollution. Over the last several decades, the Maritsa has been strongly affected by urban development and industrialization in its basin. Its bottom communities have been affected by the increasing impacts of various pollutants. Many stretches were subject to saprobic, inert, and/or toxic pollution. Factor analysis (VARIMAX-rotation) of data from 1976-1977 revealed that the most important factor determining species diversity and the structural organization of the macrozoobenthos was inert pollution (38% of total dispersion), followed by toxic (24%) and saprobic (22%) pollution. The invertebrate communities have lost 76 species recorded before 1955, and another 76 species after 1963. During the period 1976-1977, a total of 219 taxa were recorded for the macrozoobenthos of the Maritsa; in 1987, only 98 were found. At several sites the macrozoobenthos were completely absent for one or more seasons in 1987, and some taxonomic groups were not represented in samples at all (after Russev, 1966, 1968; Russev et al., 1981; Uzunov, 1981; Uzunov et al., 1981; Uzunov and Kovachev, 1985; Kovachev, 1989; Uzunov et al., 1991; etc.)

Hydrotechnical Projects

Hydrotechnical construction and other hydrological engineering works can also cause essential changes in, and damage to, the biological diversity of the aquatic ecosystems under review. In fact, however, this aspect was not well represented in the available references on the freshwater ecology of the country. Thus, the following comments are based on some general considerations.

1. Drainage

The draining of marshes and other wetlands in general causes elimination of the aquatic ecosystems as a whole: no species, no communities, no biodiversity. Many wet-lands and shallow water bodies have been completely lost, especially along the Maritsa and Tundzha Rivers and the Black Sea coast.

2. Changes in riverbeds

The straightening, diking, embankment, and walling of riverbeds can also bring about radical changes in species and cenotic diversity, as the regulatory functions within the ecosystems are redistributed from the benthic to the periphyton community. The natural flows of the rivers are redirected within artificial channels.

3. Water withdrawals

The withdraw of waters affects primarily the species diversity of the benthic communities in streams and rivers. Depending on the type of construction, it can result in the loss of species or populations whose life-cycles are linked to high waves or floods during the spring, and (in cases where all water is withdrawn) the advance of secondary succession in downstream areas.

4. Dams

The storing of river waters behind dams entails a radical change in ecosystem typology, as running waters are transformed into a standing waters. This results in a redistribution of the ecosystem regulatory functions from benthic to planktonic communities. At the species level, the rheophilic hydrobionts are replaced by limnobionts. Despite numerous references to the hydrobiology and ecology of reservoirs in the scientific literature, no actual assessments have been made of the losses and benefits of such an exchange.

Other Threats

Aquatic ecosystems face at least two other major potential threats, neither of which has been studied with respect to their possible effects on biological diversity in Bulgaria.

The trans-boundary and regional transport of air pollutants can result in damage to species diversity through acid rain and/or through the deposition of harmful substances in water bodies, on soils, and eventually in the groundwaters. Although no visible changes in cenotic and ecosystem diversity may take place, substantial negative impacts on both community structure and ecosystem function can be expected.

Global climate change, and especially global warming, might result in the loss of endemic species, as well as the more sensitive stenobiotic species and populations (in both surface and ground waters), as environmental parameters shift beyond their ecological tolerances.

Appendix 1. Codification of the River Basins Under Review

(according with the National Monitoring Network)

Black Sea Catchment Province

[30] 025: Batova River basin
[30] 026: Devnenska River basin
[30] 027: Provadizhska River basin
[30] 028: Kamchia River basin
[30] 040: Ajtoska River basin
[30] 047: Ropotamo River basin
[30] 055: Veleka River basin
[30] 100: River basins of the smaller Black Sea tributaries
[30] 101: Basins of the coastal lakes lacking their own outflow

Aegean Sea Catchment Province

[30] 059: Tundzha River basin
[30] 060: Maritsa River basin
[30] 061: Arda River basin
[30] 064: Mesta River basin
[30] 065: Strouma River basin

Note: Only the numbers after the brackets are used in the text and tables

Appendix 2. Codification of the Habitats/Ecosystems Under Review

Running Waters (Lotic Systems)

1A: Rivers, streams and brooks
1B: Artificial channels

Stagnant Waters (Lentic Systems)

2A1: Lowland lakes
2A2: Glacial mountain lakes
2A3: Brackish coastal lakes
2A4: Hyperhaline coastal lakes
2A5: Bogs, marshes, and other wetlands

2B1: Artificial lakes and reservoirs
2B2: Fish ponds
2B3: Rice fields
2B4: Cooling reservoirs
2B5: Deposition basins

Underground Waters (Phreatic Systems)

3A1: Water bodies in caves
3A2: Hyporheic habitats
3A3: Springs

3B1: Waters from well shafts and test-pits

Temporary Water Bodies (Thelms)

4A1: Lithothelms
4A2: Phytothelms
4A3: Dendrothelms
4A4: Puddles and other temporary water bodies

Appendix 3. Excerpts from the European Red Data List of Globally Threatened Animals and Plants

IUCN Global Status: E - Endangered, V - Vulnerable, I - Indeterminate, * - Taxa known to be threatened but currently under review by IUCN. (Source: UN, E/ECE/1249, NY, 1991).

HIRUDINEA

Dina absoloni Johans. BLE
Dina lineata arndti Aug. BLE

MOLLUSCA

Hauffenia lucidulus Ang. BGE

OSTRACODA

Mixtacandona elegans Daniel.& Cvet. BGE
Pseudocandona spelaea Klie BLE
Pseudocandona puteana Klie BLE

COPEPODA

Hemidiaptomus thracicus Sch. BGE

CYCLOPOIDA

Diacyclops schappuisi Naid.& Pand. BGE

HIRUDINEA

Dina absoloni Johans. BLE
Dina lineata arndti Aug. BLE

MOLLUSCA

Hauffenia lucidulus Ang. BGE

OSTRACODA

Mixtacandona elegans Daniel.& Cvet. BGE
Pseudocandona spelaea Klie BLE
Pseudocandona puteana Klie BLE

ACARI: HALACARIDAE

Soldanellonyx chappuisi thracicus Petr. BGE
Porolohmannella cvetkovi Petr. BGE
Halacarellus phreaticus Petr. BGE

ACARI: HYDRACHNELLAE

Atractides asticae Petr. BGE
Atractides longiporus Petr. BGE
Axonopsis orghidani Petr. BGE
Axonopsis boureschi Petr. BGE
Momonisia phreatica Petr. BGE
Mideopsis motasi Petr. BGE

ISOPODA

Balkanostenasellus rumelicus Cv. BGE
Microcharon apolloniacus Cv. BGE
Microcharon euridices Cv. BGE
Microcharon major Kar. BLE
Microcharon phlegetonis Cv. BGE
Microcharon thracicus Cv. BGE
Microcerberus phreaticus Cv. BGE
Microcerberus stygius harmanliensis Cv. BGE

ODONATA

Coenagrion mercuriale V
Ophiogomphus cecilia E
Gomphus flavipes I
Brachytron pratense I
Leucorrhinia pectoralis *

COLEOPTERA

Graphoderus bilineatus V

COPEPODA

Hemidiaptomus thracicus Sch. BGE

CYCLOPOIDA

Diacyclops schappuisi Naid.& Pand. BGE
Speocyclops rhodopensis Pand. BGE

HARPACTICOIDA

Bryocamptus petkovski Apost. BGE
Elaphoidella angelovi Mich. BGE
Elaphoidella borutzki Mich. BGE
Elaphoidella cvetkiovi Mich. BGE
Elaphoidella gracilis serrulata Dam. & Bot. BGE
Elaphoidella necessaria Kief. BLE
Elaphoidella valkanovi Bass. BGE
Elaphoidella pandurskyi Apost. BGE
Stigoelaphoidella michailovae Bass. BGE
Maraenobiotus bulbiseta Bass. & Apost. BGE
Nitocra stygia Apost. BGE
Nitocrella spinulosa Apost. BGE
Nitocrella stygia Apost. BGE
Nitocrella tonsa Mich. BGE

SYNCARIDA

Hexabathynella hebrica Cv. & Petr. BGE
Hexabathynella breviappendiculata Cv. BGE
Hexabathynella longiappendiculata Cv. BGE
Hexabathynella nestica Cv. BGE
Hexabathynella tenera Cv. BGE

AMPHIPODA

Gammarus frater Kar. & Pink. BGE
Gammarus shablensis Car. BGE
Niphargus cepelarensis St.& Kar. BGE
Niphargus toplicensis Andreev. BGE

* Note: Information about endemic insect species from aquatic habitats/ecosystems is presented in separate reports in this volume.

Table 1. Thematic Development of Scientific Literature (334 titles) on the Biodiversity of the Black Sea and Aegean Sea Basins During the Twentieth Century

Period 1900 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991
1910 1920 1930 1940 1950 1960 1970 1980 1990
Faunistic 1 5 6 19 11 4 18 55 54 35 7
Cenotic - - - - 2 - 9 18 29 25 -
Applied - - - - - - 6 5 10 14 1
Total 1 5 6 19 13 4 33 78 93 74 8

Table 2. Number of Recorded Species in the River Basins of Bulgaria (see Appendix 1 for codification of the river basins)

Systematic Groups Black Sea Province Aegean Province Total
025 026 027 028 040 047 055 100 101 059 060 061 064 065
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Rhizopoda     14 5 2 4   11 11   17 96 78   147
Ciliata 13 13 59 40 49 25 14 29 33 77 146 33 13 23 200
Porifera     1 1           1 5       5
Hydrozoa     12 3 2 9 1 9   1 2     2 14
Bryozoa     3 5 2 12 1 6   1 6       14
Turbellaria   3 15 3 2 5 2 12 3 3 10 4 2 5 29
Nemertini   1 2                       2
Nematomorpha 1             1     1       3
Nematoda     6 2 3   1 5 3   1       9
Rotatoria     36 6 20 7 2 39 24 52 99 21 9 10 164
Gastrotricha               1             1
Polychaeta     14 1 2 8 1 5 1           22
Oligochaeta 1 3 16 22 8 13 6 17 27 47 54 27 59 50 70
Hirudinea   2 7 5 1   1 5 2 10 14 6 3 11 17
Gastropoda 1 4 28 9 2 8 4 15   22 37 11 5 11 57
Bivalva 1 1 7 2   7 1 7 1 6 11 3 1 1 23
Tardigrada           1                 1
Hydracarina     4 8   8 75 13 20 8 61 26 5 8 124
Conchostraca                     1       1
Phyllopoda                 1           1
Ostracoda     32 3 2 7 4 19 30 3 42 8 8 2 64
Cladocera 1 1 22 4 13 28 19 42 24 41 70 30 27 13 108
Copepoda 5 2 46 8 17 37 22 41 59 44 101 20 14 21 183
Branchiopoda                 2           2
Syncarida           2 2 3   2 5   2 1 7
Mysicadea     4   1 2 1 3 1           5
Cirripedia     1   2 1   1             2
Amphipoda 2   20 9 5 9 4 15 18 8 14 12 3 8 41
Isopoda 1   4 2 3 4 3 8 2 6 11 3 4 4 17
Anizopoda           1   1             1
Decapoda 1 2 11 4 2 7 2 7 1 4 5   2 4 14
Ephemeroptera 14 7 16 58 1 29 45 46   66 89 58 37 55 90
Plecoptera       4   2 4 11   17 31 15 13 21 42
Odonata 10 55 14 22 2 7 13 51 9 27 30 23 15 25 58
Heteroptera 4   3 6   4 2 12   24 42 14 3 8 42
Trichoptera 5   10 9 3 1 19 9   38 85 71 35 70 170
Coleoptera 1   5 12 3 2 4 17   32 84 24 7 19 148
Megaloptera 1   1             1 1 1   1 1
Lepidoptera                 1   1       2
Diptera:                              
Athericidae             2     2 2 1 2 2 2
Blephariceridae               1   1 5 2 2 2 6
Ceratopogonidae     2   1 1   2   2 2 2 1 1 4
Chironomidae 3   46 18 14 14 5 34 23 85 98 57 19 127 201
Culicidae 15   9 16 1 12 7 18 6 5 15 5 1 4 35
Dixidae                   1 2 1   1 2
Limoniidae             1 1   5 4 2 4 6 7
Muscidae           1 1     1 1 2     2
Simuliidae 2   2 9   2 4 6   13 46 20 36 41 64
Varia     3 6 1 5 2 3   7 14 6 4 10 18
Total 80 40 474 303 164 282 275 526 302 662 1263 604 384 567 2240

Table 3. Number of Recorded Species in the Various Habitats in Bulgaria

Systematic Groups 1A 1B 2A1 2A2 2A3 2A4 2A5 2B1 2B2 2B3 2B4 2B5 3A1 3A2 3A3 3B1 4A1 4A2 4A3 4A4 Total
Rhizopoda     54 75 5   95 5 2         18 11           147
Ciliata 164   12 5 17 4 15 30 3 12                     200
Porifera 2         1 1       1                   5
Hydrozoa 7       8 4 4 1                         14
Bryozoa 12       13 2 2 1 2                       14
Turbellaria 10 1 1   15 4 3 1             7           29
Nemertini   1                 1 1     1           2
Nematomorpha 1       1   1                           3
Nematoda 1       5   4             2             9
Rotatoria 1   49   57 3 53 54 22         1 9         3 164
Gastrotricha         1                               1
Polychaeta 6       20 4 2                           22
Oligochaeta 63     6 31   3 12         2 6   7         70
Hirudinea 14       3   9 5   1 4                   17
Gastropoda 27   7   17 3 26 2 1   3       6         1 57
Bivalva 12       8 3 9 1             1           23
Tardigrada 1                 1                     1
Hydracarina 39   6   7 3 30 1 14 6 1     9 13 37       4 124
Conchostraca 1                                       1
Phyllopoda           1                             1
Ostracoda 1 1   5 33 5 30   9     1     11 3       9 64
Cladocera 10   35 27 46 3 60 46 20   1       1 1     1 23 106
Copepoda 19 3 21 12 55 19 62 29 15 2   2 13 28 49 21 1 1 3 30 183
Branchiopoda           2                             2
Syncardia                           2 5 3         7
Mysidacea         5   2                           5
Cirripedia         2 1                             2
Amphipoda 15   1   24 7 3 2         2 3 5 2         41
Isopoda 3       5 3 1             6 11 4         17
Anizopoda         1                               1
Decapoda 5       10 6 3 1                         14
Ephemeroptera 90   6   2   1 5 4                       90
Plecoptera 42                                       42
Odonata 34 1 11 4 2 1 33 4 4     1               15 58
Heteroptera 36   9   4   1 5 4                       42
Trichoptera 86 1 4 15 17 3 48 7 4 1     8   9   1 2   5 148
Coleoptera 162   19   2   9 2                         170
Megaloptera 1                                       1
Lepidoptera 2                                       2
Diptera:                                          
Athericidae 2                                       2
Blephariceridae 6                                       6
Ceratopogonidae 2       2                               2
Chironomidae 178       34 2 30 19 25                     2 201
Culicidae 8           17   1 1         4   3   5 17 35
Dixidae 1                                       2
Limoniidae 7                                       7
Muscidae 2                                       2
Simuliidae 64                                       64
Varia 16         2 1                           18
Total 1153 8 235 149 452 86 544 233 130 14 11 5 15 75 144 78 6 3 9 109 2240

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