Biodiversity of Non-Vascular Plants in Bulgaria

Dimitar Vodenicharov, Dobrina Temniskova-Topalova, Ivan Kirjakov, Stefka Dimitrova-Konaklieva, Rumen Mladenov, Snezhana Moncheva, Slavcho Petrov, and Dobri Ivanov

Summary

This report is divided into four sections, each of which examines a different group of organisms.

Algae

Research on algae in Bulgaria began in 1890 and still continues. This research has been carried out in different water basins and aquatic biotopes (saltwater, fresh water, running water, and still waters) as well as in soils and other non-aquatic biotopes. All categories of procaryotic and eucaryotic algae have been studied, but no type of algae can be said to have been "completely researched" according to its composition and distribution around Bulgaria. Chrysophyta, Cryptophyta, Xanthophyta, and Bacillariophyta are the least studied types. At the community level, rivers as well as some lakes and wetlands also require further investigation.

The variety of algae in Bulgaria presently encompasses about 3000 species (more than 1800 variations and forms) from approximately 550 genera of 11 groups. Three new genera, more than 60 species, and a great number of variations and forms have been described in the country. The Bulgarian algae flora can be estimated as quite rich. The draining of lakes and wetlands as well as progressive contamination are basic factors that have had adverse effects on the diversity of algae and the biocenoses essential to their existence. New protected areas are to be established in order to stop this process of deterioration.

Mosses

Research on mosses began at the turn of the century and still continues. A number of regions - the Danubian plain, Sredna Gora, etc. - are not sufficiently studied. There is also a need to review the genera that are especially difficult to examine. Diversity among the mosses that have been studied amounts to 668 species in 195 genera. There are no known endemics. Nineteen species are recognized as rare. Three protected areas with characteristic bryo-geographical elements have been established. The extensive destruction of forests has had a negative influence on the diversity of mosses. The draining of lakes and wetlands, along with other anthropogenic factors, adds to this negative effect. New protected areas for mosses have not been envisioned.

Hydatophytes, Neustophytes, and Helophytes

Research on these non-vascular plant forms has largely parallelled that of the Bulgarian flora in general. Systematic studies were carried out from the 1930s to the 1970s. These studies also provided a foundation for understanding the basic communities. Various research methods were used during different periods. Some of the water basins of the country have not yet been studied.

Altogether, 187 species have been identified: 42 (19 genera) hydatophytes, 13 (8 genera) neustophytes, 128 (69 genera) helophytes, and 4 (4 genera) hydatoneustophytes. None of these are endemics, but some are rare species and 4 species are considered extinct. The greatest diversity is found in lakes and wetlands along the Danube River, in the Black Sea, and in several of the large river valleys. The draining of lakes and wetlands has proved to be the chief negative factor, primarily in inland regions and along the Danube. Dam construction has not only had a negative impact on diversity, but has also destroyed some interesting lakes and wetlands. The proclamation of new protected areas has been planned and could have a substantial impact on the preservation of this diversity.

Lichens

Research on lichens began at the turn of the century and still continues. It is mainly concerned with the flora. These investigations have been primarily floristic in character. A number of regions (Sredna Gora, the Danubian Plain, etc.) are still not fully investigated. Some groups are not thoroughly studied or need to be reviewed. Thus far, 709 species from 147 genera have been described. It is difficult to identify endemic and rare species with substantial certainty. The main negative factor affecting lichens is the destruction of forests in a great number of regions of the country. In some regions, air pollution is also a negative influence. New protected areas have not been planned.

Algae

Background of Algae Research Research on Bulgaria's algae flora began during the last decade of the last century (Istvanffi, 1890; Petkov, 1898-1899). During the last few decades of the present century, research was continued and expanded, mainly by Stefan Petkov. He worked very hard to study the Bulgarian algae flora. His publications contain data on all divisions of the algae flora and especially on the green algae and algae with linked spores. He described a great number of new species, varieties, and forms. Almost all of his publications contain drawings of established species, thus initiating the iconography of the Bulgarian algae. While Petkov focused his research on freshwater basins, he also studied the Black Sea. Petkov published data on various regions in Bulgaria and studied more systematically and in greater detail the wetlands and lakes along the Danube (Petkov, 1911), at Vitosha Mountain (Petkov, 1922, 1928), in the Pirin Mountains (Petkov, 1925, 1929), and in the Rila Mountains (Petkov, 1939), among other areas. He also studied the unfavorable impact of anthropogenic factors on the algae flora (Petkov, 1929, etc). Petkov was the first chairman of the Union of the Protection of the Nature, which was founded in 1928.

The next stage of algae research in Bulgaria began in the 1960s. It is characterized by extensive studies that resulted in a great number of publications (see bibliography). Modern methods and principles were applied, using floristic, horologic, cenological, and ecological data. The investigators narrowed the scope of their work to focus on basic groups of algae as well as particular water basins and biotopes.

Vodenicharov directed his efforts towards freshwater ba-sins and studied in detail wetlands on Lulin Mountain (Vodenicharov, 1959); the high mountain lakes in the Rila and Pirin Mountains (Vodenicharov, 1957, 1958, 1959, 1960, 1962); the lakes and wetlands of the Rhodope Mountains (Kirjakov and Vodenicharov, 1984, 1987, 1988); and certain rivers (Vodenicharov and Kirjakov, 1986, 1987). These studies focused mainly on green algae, algae with linked spores, blue-green algae, and freshwater red algae (Vodenicharov, 1960; Vodenicharov et al., 1991), and resulted in the description of new genera (Vodenicharov and Benderliev, 1971; Vodenicharov, 1989) and species (Vodenicharov, 1960, 1963; Vodenicharov and Kirjakov, 1970, 1986; Vodenicharov and Benderliev, 1971; and others).

Petrova's research focused entirely on phytoplankton in the Black Sea and some seaside lakes (Petrova, 1959-1971; Petrova-Karadzova, 1973-1993). She published abundant information on the composition and qualitative and quantitative dynamics of algal populations. She pointed out the periodic changes in these populations, and attributed them to solar activity and to the tendency towards eutrophication under the influence of anthropogenic factors. We base our comparisons, estimations, and discoveries on her systematic and continuous research. Research in the last few years on the phytoplankton, and especially algae "blooms," in the Black Sea has been performed primarily by Moncheva (Moncheva, 1987-1992).

Draganov studied the cave and soil blue-green algae (Draganov, 1960-1981), describing some new species (Draganov, 1964, 1968, 1985) and algae cenoses (Draganov, 1977). Lately he has focused his research on the algae of the Danube River and adjacent wetlands and lakes (Draganov et al., 1987; Draganov and Stoyneva, 1988-1991). This research is presently being conducted by Stoyneva (Stoyneva, 1987-1991).

Temniskova published floristic and ecologic data on temporary water basins and rice-fields (Temniskova-Topalova, 1967, 1968). She first studied flagellate groups of algae (Temniskova-Topalova, 1965-1975), but later focused on flint algae (Temniskova-Topalova and Misaleva, 1982; Temniskova-Topalova and Dimitrova, 1988), primarily fossil species.

Dimitrova studied predominantly the Black sea macrophytes. She investigated in detail their composition and distribution, analyzed the geographic elements, and attempted to define areas of the Bulgarian coast on the basis of macrophytobenthos (Dimitrova, 1969; Dimitrova-Konaklieva, 1973-1987, etc.).

Kirjakov has been considered the most outstanding researcher of the Bulgarian algae flora over the last two decades. He has published extensive floristic and horologic data on different groups of freshwater algae, primarily green, blue-green, and lately Euglenophyta and freshwater red algae (Kirjakov, 1969-1989). He has placed special emphasis on the difficult genera Scenedesmus (Kirjakov, 1976, 1978, 1980) and also described several new species (Kirjakov, 1970, 1983, 1989). He has studied in detail the algae flora in lakes and wetlands in the Rhodope Mountains (Kirjakov and Vodenicharov, 1984, 1987, 1988) and in several rivers (Kirjakov and Vodenicharov, 1986), as well as the phytoplankton of fish-breeding basins.

The famous Bulgarian hydrobiologist Valkanov performed extensive research dedicated to flagellate heterotrophic and autotrophic organisms. He also described new species and genera (Valkanov, 1926-1968) and provided significant assistance to investigations of wetlands and lakes, especially in the high mountains and along the Black Sea coast (see below).

The phytoplankton in artificial and natural water basins in Bulgaria have been studied mainly by hydrobiologists (Najdenov and Sais, 1977, 1985; Sais, 1977, 1978; etc.). Algae were used as bio-indicators in a number of publications concerned with the assessment of biological conditions in the water basins in Bulgaria (e.g., Angelov, 1964, 1968; Draganov and Stoynova, 1991; Vodenicharov and Kirjakov, 1986, 1987). Several foreign scientists have researched algae in the Black Sea and freshwater basins (Lepsi, 1925-1931; Roubal, 1947; Starmach, 1964, 1969; Kawecka, 1974, 1976). Vodenicharov et al. (1971) provided a partial summary of this knowledge in the Flora of Bulgaria, though it requires substantial supplements.

Gaps in Knowledge

The algae flora of Bulgaria is relatively well studied. Research has been undertaken on all sections of prokaryotic and eukaryotic algae, although we cannot consider this work complete. The flagellate forms (Chrysophyta, Cryptophyta, Dinophyta, as well green algae) have been studied the least. We rely strongly on research on the flint algae and on the systematic and critical investigation of difficult groups such as Desmidiales, Zygnemales, Chlorococcales, and filiform green algae.

Various water basins have been studied, but the data is quite scanty, especially on the algae of both small and big rivers (the Maritsa, Strouma, Tundzha, Mesta, and the tributaries of the Danube). A number of regions can be regarded as insufficiently researched - the Danubian plain (and some other plains), Sredna Gora, the Western Border Mountains, and parts of the Stara Planina Mountains.

Typically, research on a particular water basin or region has been performed only once. This greatly hinders or makes impossible precise modern evaluations and the delineation of the changes that have taken place over time. Research, it should also be noted, has employed various methods and has focused on particular groups (while the flint algae have been most often excluded).

Diversity of Algae

A total of about 3000 algae species, in approximately 550 genera, have been discovered in various water basins and non-aquatic biotopes in Bulgaria. These are classified in 11 sections - one prokaryotic and 10 eukaryotic (Table 1). More than 1800 varieties and forms are described. Three genera, more than 60 species, and many varieties and forms previously unknown were discovered in the course of research of Bulgaria's algae flora. Some of these are included in the European monographs, guides, and floras. The algae flora in Bulgaria may thus be characterized as highly diverse. The reasons for this can be attributed to the diversity of water basins and of physical and geographic conditions.

Rare and Endemic Species

There is a widespread view that algae are cosmopolitan in their distributions. However, many species are found only under particular ecological conditions, and in certain biotopes and water basins. On the other hand, the lack of sufficiently complete and systematically collected data for Bulgaria makes the identification of particular species as "endemic" and "rare" very difficult and uncertain. Hence, such categories of algae species are not presented here (except for the macrophytes of the Black Sea; see below).

Freshwater Algae

Various types of water basins and biocenoses in Bulgaria are of great interest in characterizing the biological diversity of algae and in estimating the danger of losses, changes, and even extinctions of species.

There are many high mountain lakes in Bulgaria of glacial origin. Most are small, shallow, and not very rich in algae. The algae flora of these lakes has many specific features and differs greatly from the flora of other lakes in Bulgaria. Some areas, and even whole lakes, that have been heavily silted have turned into wetlands and support a greater abundance of algae species. Some high mountain lakes in the Urdinia cirque in the Rila Mountains have been thoroughly researched and their characteristic algae communities fully described.

Two groups of mountain lakes and wetlands in Bulgaria - Smolyanski and Chairski - have been most thoroughly studied. More than 750 species, varieties, and forms from about 190 genera of eukaryotic and prokaryotic algae have been discovered in them, including genera and species previously unknown. This flora as a whole has many unique features, including an interesting component of hydatophytes, neustophytes, and helophytes.

There is little recent information concerning the lakes and wetlands along the Danube River and the Black Sea. The last summary was published 30 years ago (Ivanov et al., 1964). These water bodies all have diverse and abundant algae floras, mainly characteristic of eutrophic lakes. They have many unique features when compared to other groups of lakes, and in assessing them as endangered lakes, the presence of hydatophytes, neustophytes, and helophytes in them should be considered.

As mentioned above, the algae flora of rivers is poorly studied. Some have been shown to contain diverse and abundant species of freshwater red algae, and it is likely that flint algae will be shown to play an important role in all of them. Of great interest are mountain rivers and streams that support characteristic rheophiles and that have been affected relatively slightly by pollution.

Black Sea Algae

As a result of long years of systematic investigations, we have much data available concerning the Black Sea, especially as regards its phytoplankton. The phytoplankton in the Black Sea and elsewhere in Bulgaria consist mainly of the Bacillariophyta and Dinophyta. Chrystophyta, Euglenophyta, Chlorophyta and Cynophyta are also present. In the period 1981-1990, a total of 134 species, varieties, and forms were discovered along the Bulgarian coastline, including 67 Bacillariophyta and 56 Dinophyta. This diversity is not uniform in the different regions. For example, studies conducted in the years 1983-1986 revealed 111 species, varieties, and forms in Varna Bay, while in the nearby region of Cape Kaliakra only 68 were found. The level of phytoplankton diversity is probably lowest in Bourgas Bay.

Over the period 1954-1990, the composition of Black Sea phytoplankton has undergone substantial changes. A change in the relationship between the Bacillariophyta and Dinophyta has been determined. The formerly dominant Bacillariophyta have gradually been overcome by the Dinophyta. This is true in terms of both number and biomass. In the years 1954-1970, the biomass of the Bacillariophyta exceeded by 10 times that of the Dinophyta; in the period 1971-1990 this situation reversed as the Dinophyta exceeded the Bacillariophyta by about 4 times. In addition, the Prorocentrum minimum (Exuviella cordata) appeared near the coasts and began to play an important role. In coastal water basins, ports, and bays, local algae blooms occurred every year and every season, and even became permanent; at the same time, regional blooms in the open water areas have shown cyclic development.

Changes in the phytoplankton community of open water areas are related to cyclic changes in hydrometereologic factors and solar activity. Changes in the composition, number, and biomass of phytoplankton in coastal areas are due to the progressive process of eutrophication under the influence of natural and anthropogenic factors. Eutrophication results in blooms, some of which have had catastrophic effects. "Red tides" have appeared since 1971.

A total of 157 species are included in the composition of the Black Sea macrophyte benthos, which in turn constitutes about 53% of the macrophyte flora of the Black Sea. These species belong to 82 genera, 43 families, and 25 orders of the sections Rhodophyta, Phaeophyta and Chlorophyta. The first section is most thoroughly represented (55% of all species); the other two are represented by approximately equal numbers of species.

Fourteen Black Sea floristic regions can be identified on the basis of the microphytes. One is the Bulgarian Black Sea coast, which ranks fourth in abundance of species after the southern coast of Crimea, Sevastopol Bay, and the Novorus-siiski Bay. A substantial portion of the macrophyte species along our coast are widely spread, though some are characteristic of particular areas. Red algae dominate in all areas of the Bulgarian Black Sea coast, the spring flora being the most abundant.

This review is based on data collected prior to 1977. The picture has since changed in essential ways (according to unpublished data by Dimitrova offered especially for this report). A considerable decrease in populations has been observed and a complete extinction of some species. For several years it has been rare to find along the Bulgarian coasts Dasya bayloviana, Padin pavonia, Nemalion helminthoides, Cladostephus verticillatus, Laurencia pinnatifida, Dilophus fasciola, and other species. Extinction of the populations of Cystoseira barbata and Cystoseira crinita in some regions has been established.

Gelidiela antipai, Laurencia coronopus, Desmotrichum punctarioides, Enteromorpha meotica are macrophytes on the Bulgarian coast that are endemic to the Black Sea.

Twenty-two species are rare or endangered (Table 2).

Sixteen species can be considered economically valuable (Table 3). The microphytobenthos was studied only in relation to the flint algae. A total of 385 species, varieties, and forms from 61 genera were identified. Podosira pellucida is the only dominant in the surface bottom sediments of the Bulgarian shelf.

Threats to the Algae Flora

Considerable changes in vegetation take place in connection with the natural silting of lakes and wetlands. Different stages of these processes can be observed in many lakes and wetlands in Bulgaria. The effects of siltation generally begin at the periphery and progress towards the interior. However, in lakes in the Rhodope Mountains, these effects have been observed to start at the center.

Changes caused by anthropogenic factors are the greatest and the fastest. Such factors including drying, drainage, and construction. Many water basins suffer particularly from strong unfavorable influences that have increased over the last several decades - the pollution caused by industrialization, the intensification of agriculture, and the growth of cities. A number of karstic springs with interesting algae flora have disappeared as a result of damming of the water. There are almost no thermal springs remaining in Bulgaria whose water is not retained by dams.

Recommendations

In order to protect the diversity of algae species and communities, it is necessary above all to observe strictly the statute regarding existing protected areas, and particularly those in which there are water basins. Moreover, we believe that it is necessary to declare new protected areas. Listed here are three areas in which algae flora and vegetation are especially important. Other areas, connected with the hydatophytes, neustophytes, and helophytes, are noted later in this paper.

1. The springs of the Mladezhka River and the river itself near the village Mladezhko in the Strandzha Mountain region. This part of the river is very rich in different freshwater red algae. Such abundance is not known in other regions of the country.

2. The area of Markovi Kladentsi in the Ograzhden Mountain area. Rare species of flint algae and a relatively diverse flora are found here.

3. In the region of the village Varvara near the mouth of the Veleka River. In this region of the Bulgarian Black Sea coast about two-thirds of all species of macrophytes are concentrated. A great number of endemic and rare species for the Black Sea are found here.

Mosses

Background of Bryological Research Research on the moss flora of Bulgaria began in the early 1900s (Velenovski, 1902; Kovachev, 1902, 1905) and continued under both Bulgarian (mainly Arnaudoff, 1909-1914) and foreign scholars (see bibliography). It has intensified in the second half of the century (primarily Petrov, 1955-1986). The information on the moss flora was summarized in the Guide to the Mosses of Bulgaria (Petrov, 1975).

Research on mosses has focused primarily on the taxonomic components in different regions of the country. The Vitosha, Pirin, Strandzha, Belasitsa, Rhodope, and other mountains are the best studied areas. The bryogeographical investigations have been published since the 1950s (e.g., Petrov, 1955, 1958, 1986). Petrov (1975) provided a review of the studies of the moss flora.

Gaps in Knowledge

In general, the bryoflora of Bulgaria and the chorology of the different species have not yet been sufficiently studied. Until recently, bryological studies were not undertaken systematically or on a wide scale. There have been almost no recurrent or continuing studies in any one region. As a result, the data are insufficient to draw conclusions about historical changes and trends.

The least studied areas are the Danubian plain, southeastern Bulgaria, the western border forests, Sredna Gora, and the southernmost regions of the valleys along the Strouma, Mesta, and Maritsa Rivers. More thorough studies of some difficult genera - Riccia, Lophozia, Marsupella, Scapania, Cephaloziella, Sphagnum, Tortulla, Pholia, Bryum, Plagyothecium - are needed.

Moss Diversity

The moss flora of Bulgaria consists of a total of 668 species from 195 genera and 69 families (Table 4). The family Ricciaceae in the subclass Marchantiidae contains the most species; 10 out of the 11 species in this family are from the genus Riccia. The families Lophoziaceae (25 genera; 13 species from the genus of Lophozia) and Scapaniaceae (19 genera; 16 species from Scapania) are the most species-rich in the subclass Jungermanniidae. The subclass of Sphagnidae is fairly well represented in our bryoflora, with 23 species. The greatest diversity at the subclass level is found within the Bryidae. The most diverse families are Pottiaceae (20 genera, 66 species) and Dicranaceae (19 genera, 51 species). Six other families include more than 20 species: Grimmiaceae, Bryaceae, Orthatrichaceae, Amblystegiaceae, Brachytheciaceae, and Hypnaceae. The Bulgarian bryoflora can thus be considered relatively rich for a country located in the temperate zone.

Many Bulgarian mosses are found only in particular regions. It would be premature to classify them as "rare," since present studies do not cover equally all floristic regions of the country. However, a limited number (19) of species can be designated as "rare" (Table 5). All of these are illustrated in Petrov (1975) and represented in the bryological section of the herbarium of the Institute of Botany at the Bulgarian Academy of Sciences. With regard to these species, and given the types of habitats where they occur, it is virtually certain that future, more detailed studies will not increase the number of their locations.

Some of the more characteristic bryogeographic elements can be found in the Bistritsa Reserve (Vitosha Mountain), the Parangalitsa Reserve (Rila Mountains), and the Tisata Reserve (the Kresna Gorge in the valley of the Strouma River). (See Table 6).

Threats to the Moss Flora

A number of factors have influenced and still have an adverse effect on the moss diversity in Bulgaria. The main negative factor is the destruction of forests in many regions of the country, beginning centuries ago but continuing into the present. The most severely affected forests are in the lowland regions and the low forest belts. The distribution of a number of forest species is restricted in this way. This might also be why some species of our moss flora went extinct or are in danger of extinction.

The partial or complete systematic drainage of water basins and wetland areas, beginning in the first decades of this century, has also had a negative impact on the diversity of the moss flora in Bulgaria. This has resulted in drastic changes in the microclimate of the respective regions and the destruction of the habitats of certain moss species.

The construction of large dams ("Iskar" in the Sofia region, "Topolnitsa" close to Srednogorie, "G. Dimitrov" in the Kazanlak region, and others) changes the microclimate and destroys areas that support moss vegetation. The construction of roads and highways, the growth of the cities, and high levels of air pollution (particularly in certain regions) are other negative factors influencing moss diversity in Bulgaria.

The preservation and maintenance of existing protected areas contributes to the retention of Bulgaria's moss diversity. No suggestions for new protected areas have been made so far in connection with the mosses.

Hydatophytes, Neustophytes, and Helophytes

Background of Research

Research on higher plants in and around water basins is currently performed as part of general botanical research in Bulgaria. These studies are floristic and horologic in nature, and are summarized in the Flora of the People's Republic of Bulgaria, 1963-1989; Kitanov and Penev, 1963; Stojanov et al., 1966-1967; Kitanov and Kitanov, 1990, and other publications.

The first systematic investigations on hydatophytes, neustophytes, and helophytes in Bulgaria were undertaken about 1930 (Jordanov, 1929-1931). In addition to floristic and horologic studies, they included phytogeographic and ecological analyses. Some of the wetlands and lakes inside the country (Straldzhansko in Iambolsko, Dragomansko, Aldomirovsko and Kazichensko in Sofiisko, etc.) were described in greater detail.

Some algological (Petkoff 1911, 1938, 1939; Vodenicharov, 1962) and hydrobiological publications (Valkanov, 1932; Michajlova-Nejcheva, 1961) include data on hydatophytes, neustophytes, and helophytes from a number of lakes, wetlands, river basins, and dam sites. Since 1970, more extensive phytocenological and ecological studies have been conducted. As a result of these studies, 45 formations with 71 associations have been identified. A number of questions concerning the development of the communities and the influence of anthropogenic factors have been clarified, including the origin and establishment of plants in artificial water basins. Other investigations have examined the primary biological productivity of several widely distributed communities and their dominant species. The necessity of preserving diversity and some characteristic ecosystems have also been explored. Kochev and Jordanov (1981) provides a summary of this information. Vodenicharov (1959) contributed a brief guide to the hydatophytes, neustophytes, and helophytes. Ivanov et al. (1964) reviewed the flora of the lakes and wetlands of Bulgaria.

Gaps in Knowledge

Essential gaps in knowledge result from the lack of systematic research on the water basins in Bulgaria. Research has been done at different times with different objectives and methods. Thus, the available information is incomplete and heterogeneous. It does not offer a solid basis for comparative analysis or for estimates of changes in the biological diversity and communities of particular water basins. Only a few investigators have made special efforts to do systematic and continuous research.

Diversity of Hydatophytes, Neustophytes, and Helophytes

The Bulgarian flora includes 187 species of hydatophytes, neustophytes and helophytes (Table 7): 42 species of hydatophytes from 19 genera and 16 families; 13 species of neustophytes from 8 genera and 6 families; 4 species of hydato-neustophytes from 4 genera and 3 families; and, most numerous, 128 species of helophytes from 69 genera and 30 families (Kochev and Jordanov, 1981). It should be noted that the differentiation of helophytes from hydrohygrophytes is not always sufficiently clear.

Altogether, the hydatophytes, neustophytes, and helophytes constitute about 5% of the composition of the Bulgarian flora. Thirty-eight species have been declared endangered, rare, and extinct (5% of all species included in the 1984 Red Data Book of the People's Republic of Bulgaria, Vol. I. Plants): 13 hydatophytes, 7 neustophytes, and 18 helophytes. There are no endemics for Bulgaria or the Balkan peninsula among these groups. Only 3 species (Nymphaea alba, Nuphar luteum, Trapa natans) are protected by law. Four species (out of 29 altogether for Bulgaria) - Caldesia parnassifolia, Salix rosmarinifolia, Peucedanum paluster, and Hottonia palustris - are considered extinct. Small, isolated regions of distribution in Bulgaria are known for some species.

Although the hydatophytes, neustophytes, and helophytes constitute an insignificant part of the Bulgarian flora, they deserve special attention. They play an important part, along with algae, in aquatic and wetland communities (especially as primary producers and as cover and reproductive sites for animals). They also deserve attention in relation to the unfavorable changes that many water basins are experiencing. The diversity of hydatophytes and neustophytes is concentrated in the lakes and wetlands along the Danube River and the Black Sea. In some of these aquatic communities, the population of certain species is particularly high. There are few lakes in the interior of the country, and the artificial ones (created by dams) are in general deficient in hydatophytes and neustophytes. Helophytes can be found in the Danube River and Black Sea, along some river basins (especially the Maritsa River), and in the mouths of some rivers (e.g., the Kamchia and Ropotamo). Only a few species are found along the Bulgarian coast of the Black Sea: Zostera marina, Zostera nana, Potamogeton pectinatus, Zannichellia palustris, Ruppia maritima, and Ruppia cirrhosa.

There are many small high mountain lakes in Bulgaria (more than 200 in the Rila and Pirin Mountains). The species diversity in these lakes is limited, but a number of species, such as Isoetes setacea, Subularia aquatica, and Sparganium angustifolium, occur only in these lakes.

Threats to Hydatophytes, Neustophytes, and Helophytes

Natural water basins occupy considerably less of Bulgaria's territory today than they did at the beginning of the century. There were about 200,000 hectares of natural water basins and wetlands at the turn of the century (Kochev, 1989); by the 1960s only about 11,000 hectares remained (Ivanov et al., 1964). Other authors point out that these data are incomplete, since not all water basins - or what was left of them - were considered (Kochev, 1989). There is no doubt, however, that the total area of aquatic ecosystems in this country has decreased drastically in recent decades.

This decrease has become a major factor influencing negatively the diversity and distribution of hydatophytes, neustophytes, and helophytes in Bulgaria. It is connected with the gradual increase in drainage in Bulgaria since the first decades of this century, undertaken to increase the amount of arable land in the country. This resulted in the complete destruction or substantial drying up of many interior water basins (e.g., the Dragomansko blato, the Straldz-hansko blato, and the Chokluovo blato). Most extensively affected are the wetlands and lakes along the Danube river (e.g., Archarsko, Tsibarsko, Ostrovsko, Svishtovsko, and Bardimsko).

Similar alterations have affected, to a somewhat lesser extent, wetlands and lakes along the Black Sea coast (e.g., Pomoriisko, Diavolsko, and Karaachko). Such decreases in the area of these aquatic communities restrict the distribution of the plants characteristic for them. As a result, several species have become extinct in Bulgaria. In this manner, Caldesia parnassifolia and Aldrovanda vesiculosa disappeared along with the Dragomansko blato (the latter species was found in Srebarna Lake during more precise floristic investigations undertaken in the last few years; see Bajeva, 1988). The drainage of the Kazichensko blato resulted in the extinction of Hottonia palustris. Similarly, the destruction of the Chokluovo blato led to the extinction of Peucedanum palustre and Salix rasmarinifolia.

Another factor affecting negatively the distribution and (especially) the composition of the hydatophytes and neustophytes is the building of dams. About 1800 small and 30 large dams were built in Bulgaria prior to 1962. Ten of these created reservoirs with areas greater than 5 km² (comprising a total of about 178 km²). Some interesting wetlands were flooded by these dams. For example, the "Batak" dam destroyed the Batashko blato. A number of interesting species were extirpated as a result, including Nymphaea alba (a protected species!). The "Rabisha" dam has flooded the wetland of Rabishko (in the area of Belogradchishko), where a very interesting population of Nuphar luteum (another protected species!) could be found. The artificial water ba-sins are very poor in hydatophytes and neustophytes, and even in helophytes in general. This is due to the periodic and substantial changes in the water level and the slow rate of reproduction and stabilization in the flora and vegetation.

Another major factor that has had, and continues to have, a negative effect is the contamination of water basins by waste water from industrial enterprises, utilities, livestock operations, and the extensive use of fertilizers on arable lands. This results in considerable changes in the physical and chemical conditions - and therefore in the flora and vegetation - of rivers, lakes, and wetlands. Eutrophication affects most of the country's natural and artificial water basins. Specific components of the flora and vegetation in the Bulgarian lakes, wetlands, and rivers have disappeared. Some water basins are devoid of living organisms or support only the most resistant species.

Recommendations

Above all, the statute governing important existing protected areas - including the Srebarna Reserve (Silistrensko), the Arkutino Reserve (Burgasko), and the Marichini Ezera Reserve (Rila Mountains) - should be strictly observed in order to preserve the hydatophytes, neustophytes, and helophytes, as well as the communities in which they are included.

Additional protected areas need to be established (Kochev and Jordanov, 1981; Kochev, 1989). This will ensure better protection not only of certain species, but also of the communities that are characteristic of the different types of water basins in Bulgaria. Areas requiring special attention include:

1. High mountain lakes.

High mountain lakes are located within the boundaries of the Pirin and Rila National Parks. Despite this protected status, it is necessary to provide special protection for the following groups of lakes:

• Urdini ezera (NW Rila Mts.). These lakes contain, in addition to hydatophytes such as Sparganium angustifolium, Utrivularia minor, Subularia aquatica, and Callitriche palustris, a rich algae flora. There are communities that include Primula deorum, Primula farinosa, Leontodon riloense, and other close relatives. The cirques contain portions of the marble veins that are rarely found in the Rila Mountains, and that support special floristic elements.
  
  
• Popovi and Kremenski Lakes (in the central part of the Pirin Mts.), which have a rich flora that includes hyda-tophytes and algae, some of which are very rare (Isoetes, Nostoc Zetterstedtii, etc.).

2. Mountain lakes and wetlands.

• The Smolianski (above the town of Smolian) and Chairski (Devinsko) lakes and wetlands. They have a very rich flora that includes rare species such as Utricularia vulgaris, Carex limosa, Potentilla palustris, Drosera rotudifolia, Menyanthes trifoliata, and Sparganium minimum.

3. Lakes and wetlands along the Danube River (according to Kochev and Jordanov, 1981)

• Martvo blato (close to Belene)
• Blato Kayakush (Svishtovsko)
• part of the lake located close to the village of Batin (Roussensko)
• the lake Malak Preslavets (Silistrensko)

4. Lakes and wetlands along the Black Sea coast (partly according to Kochev and Jordanov, 1981)

• Durankulashko (Blatnishko) lake (only the eastern area)
• Shablensko lake (see also section on algae above)

5. Lakes and wetlands in the interior part of the country

• Aldomirovsko (Sofiisko)

Suggestions have been made to restore some of the lakes and wetlands that had been drained, such as the wetland of Chokluovo blato. Further discussions of this idea and its potential need to be undertaken.

Certain individual species not found in the existing or suggested new protected areas are also suggested for sug-gested for listing as protected species (Kochev and Jordanov, 1981). Fourteen of these species are listed in Table 8.

Lichens

Background of Research on Lichens

Research on lichens in Bulgaria began at the turn of this century under Kazandzhiev (1900, 1906). Nikolov, another Bulgarian, also worked in this area (Nikolov, 1928-1937). Several foreign scholars conducted research as well (see the bibliography). A summary of research undertaken before the 1960s can be found in Flora of Bulgaria. Lichens. (Popnikolov and Zelesova, 1964). Research on lichens has continued up to the present.

Research has mainly involved the collection of speci-mens from various regions and publication of the results. Certain regions have been studied in greater detail - Vitosha Mountain (Nikolov, 1931), Zapadna Stara Mountain and Vrachanski Balkan (Nikolov, 1937), Slavyanka and Belasitsa Mountains (Nikolov, 1937), and the Pirin Mountains (Iva-nov, 1990). Only the genus Usnea has been studied monographically (Motyka and Zelesova, 1962). The fol-lowing mountains have been studied in the same way: the Rhodopes, Rilas, Pirins, and Vitosha, as well as some parts of the Stara Planina Mountains and Black Sea coast.

Gaps in Knowledge

The diversity of lichens is not yet well studied in some regions, including the Western Border Mountains, Sredna Gora, the Danubian plain, and a substantial part of the Rhodope Mountains.

Caliciales (Collemataceae), which are currently thought to occur mainly in the vicinity of the Mediterranean sea, are not sufficiently investigated. The cristose lichens, and more particularly those located on limestone rocks (Verrucaria, Aspicilia, Caloplaca) also require further study. The data on such difficult groups as Lecideacea and Alectoria needs to be reviewed and updated.

Further expansion and development of studies is rather difficult due to the lack of an efficient herbarium in Bulgaria.

Diversity and Endemism

Thus far, 709 species of lichen have been found in Bulgaria (Popnikolov and Zelesova, 1964; Ivanov, unpub. data, 1993). They belong to 147 genera from 51 families (Table 9). The majority of genera (101) and species (564) belong to the order Lecanorales.

Most of the species in Bulgaria have been reported at only one locality. This is usually a reflection of the lack of thorough and systematic investigations. Therefore, rare species cannot be identified with sufficient certainty. Based on the data in the literature (Popnikolov and Zelesova, 1964), the 25 species listed in Table 10 may be considered as such.

There are only a few endemics among the lichens of Bulgaria. This is due to their wide ecological ranges and preferences for particular substrata. If we take into account the insufficient amount of research on our lichen flora and that of the Balkan peninsula, we can assume endemism for the time being for those taxa that have been described in Bulgaria, and for which there are no records of occurrence outside Bulgaria. With the exception of Pertusaria kasandjeffii (a species that also occurs outside of Bulgaria), this includes 14 taxa (Table 11).

Threats to Lichen Diversity

A number of factors have adversely affected lichen diversity in Bulgaria. The destruction of forests in many regions (especially the lowlands and the low mountain belts) has proved to be a crucial factor in the extinction of lichens requiring specific substrata and microclimatic conditions. The construction of dams, highways, and roads also narrows the diversity of substrata and changes the microclimate. Urban expansion and air pollution resulting from the industrialization of the country are among the most powerful negative factors. Whole regions of the country suffer from intensive air pollution (e.g., Srednogorie, Devnia, and Dimitrovgrad).

Recommendations

The preservation and maintenance of existing protected areas ensures to a large extent the protection of the lichen diversity. No new protected areas are recommended at this time.

Table 1. Biodiversity in Bulgaria: Algae

Division	Order	Family	Genus	Species	Var. + Forms
Cyanophyta	9	27	57	368	84
Rhodophyta	9	23	43	154	24
Chrysophyta (incl.Primnesiophyta)	7	20	49	107	5
Xanthophyta (incl.Eustigmatophyta)	4	12	20	67	9
Bacillariophyta	8	30	77	524	852
Phaeophyta	9	15	26	43	6
Cryptophyta	1	1	4	10	2
Dinophyta	3	3	25	125	8
Euglenophyta	2	5	23	245	120
Chlorophyta (incl.Zygnemophyta)	17	51	218	1339	717
Charophyta	1	1	5	16	3
Total	70	188	547	2998	1830

Table 2. Rare and Endangered Black Sea Macrophytes

Nemalion helminthoides (Vell.) Batt.	Cladostephus verticillatus (Lightf.) Ag.
Apoglossum ruscifolium (Turn.) J. Ag.	Stilophora rhizodes (Ehrh.) J. Ag.
Dasya baylouviana (Gmel.) Mont.	Punctaria plantaginea (Roth) Grev.
Dasyopsis spinelia (Ag.) Zanard	Dilophus fascioia (Roth) Howe
Gracilaria verrucosa (Huds.) Papenf.	Dilophus ligulata (Kütz.) Feldm.
Chondrya tenuissima (Good. et Wood) Ag.	Padina pavonia (L.) Gaill.
Chondrya dasyphylla (Wood.) Ag.	Enteromorpha flexuosa (Wulf.) J. Ag.
Laurencia pinnatifida (Gmel.) Lamour.	Enteromorpha clathrata (Roth) Grev.
Nereia filiformis (J. Ag.) Zanard.	Cladophora coelothrix Kütz.
Striaria attenuata (Ag.) Grev.	Chaetomorpha aerea (Dillw.) Kütz.
Petalonia zosterifolia (Reinke) Kuntze	Bryopsis plumosa (Huds.) Kütz.

Table 3. Economically Important Black Sea Macrophytes

Porphyra leucosticta Thor.	Laurencia obtusa (Huds.) Lamour.
Gelidium latifolium (Grev.) Born. et Thur.	Cystoseira barbata (Good et Wood.) Ag.
Gymnogongrus griffithsiae (Turn.) Mart.	Cystoseira crinita Bory
Phyllophora nervosa (DC.) Grev.	Ulva rigida Ag.
Polysiphonia subulifera (Ag.) Harv.	Enteromorpha linza (L.) J. Ag.
Polysiphonia denudata (Dillw.) Kütz.	Chaetomorpha linum (Müll.) Kütz.
Ceramium rubrum (Huds.) Ag.	Cladophora vagabunda (L.) Hoek
Ceramium diaphanum (Lightf.) Roth	Cladophora sericea (Huds.) Kütz.

Table 4. Biodiversity in Bulgaria: Mosses

Class and sub-class	Order	Family	Genus	Species
Anthoceratopsida	1	1	2	2
Marchantiopsida
Marchantiidae	1	9	13	26
Jungermanniidae	2	23	40	139
Bryopsida
Sphagnidae	1	1	1	23
Andreaeidae	1	1	1	1
Bryidae	14	34	138	477
Total	20	69	195	668

Table 5. Rare Species of Mosses in Bulgaria

Mannia androgyna (L.) Evans	Grimmia torquata Hornsch. ex Grev.
Riccia crustata Corb.	Bryum canariense Brid.
Fossombronia husnotii Corb.	Aulacomnium androgynum (Hedw.) Schwaegr.
Scapania verrucosa Heeg.	Helodium blandowii (Web. et Mohr) Warnst.
Mylia anomala (Hook.) S. Gray	Scorpdium scorpioides (Hedw.) Limpr.
Jungermannia exsertifolia Stef. ssp. cordifolia (Dum.) Vana	Calliergon giganteum (Schimp.) Kindb.
Pedinophyllum interruptum (Nees) Kaal.	Scorpiurium circinatum (Brid.) Fleisch. et Loeske
Buxbaumia aphylla Hedw.	Ctenidium procerrimum (Mol.) Lindb.
Dicranum polysetum Sw.	Orthothecium rufescens (Brid.) B., S. et G.
Schistidium agassizii Sull. et Lesg.

Table 6. Bryogeographic Elements in Protected Areas in Bulgaria

1. Bistritsa Reserve (Vitosha Mountain)
Gymnomitrium concinnatum (Lightf.) Corda, Calypogeia sphagnicola (H. Arn. et J. Perss.) Warnst. et Loeske, Blepharostoma trichophyllum (L.) Dum., Trichocolea tomentella (Ehrh.) Dum., Andreaea rupestris Hedw., Tortula norvegica (Web.) Wahlenb. ex Lindb.,	Desmatodon latifolius (Hedw.) Brid., Orthottrichum stellatum Brid., Bryum gemmiparum De Not., Helodium blandowii (Web. et Mohr) Warnst., Homalothecium nitens (Hedw.) Robins.
2. Parangalitsa Reserve (Rila Mountains)
Eremonotus myriocarpus (Carring.) Pears., Marsupella adusta (Nees emend. Limpr.) Spruce, Gymnomitrion apiculatum (Schiffn.) K. Mull., Polytrichum sexangulare Brid., Dicranum tauricum Sap., Oxystegus tenuirostris	(Hook. et Tayl.) A.J.E. Sm., Hydrogrimmia mollis (B., S. et G.) Loeske, Blindia acuta (Hedw.) B., S. et G., Orthotrichum obtusifolium Brid., Philonotis rigida Brid., Hydrohypnum smithii (Sw.) Broth.
3. Tisata Reserve (Kresna gorge in the Strouma River valley)
Targionia hypophylla L., Oxymitra paleacea Bisch. ex Lindenb., Riccia gougetiana Durieu et Mont., Tortula laevipilla (Brid.) Schwaegr., Tortula papilosa Wils.	Crossidium squamigerum (Viv.) Jur., Pottia starckeana (Hedw.) C. Mull., Grimmia laevigata (Brid.) Brid., Funaria muhlenbergii Turn.

Table 7. Biodiversity in Bulgaria: Hydatophytes, Neustophytes, and Helophytes

1. Hydatophytes	Hydrocharitaceae
Lycopodiophyta	Elodea canadensis Michx. Vallisneria spiralis L.
Isoetaceae	Ranunculaceae
Isoetes setacea	Ranunculus aquatilis L. Ranunculus trichophyllus Chaix
Magnoliophyta	Ceratophyllaceae
Potamogetonaceae	Ceratophyllum demersum L. Ceratophyllum muricatum Cham. Ceratophyllum submersum L.
Potamogeton gramineus L. Potamogeton lucens L. Potamogeton praelongus Wulfen Potamogeton perfoliatus L. Potamogeton crispus L. Potamogeton friesii Rupr. Potamogeton acutifolius Link Potamogeton pusillus L. Potamogeton trichoides Cham. et Schlecht. Potamogeton pectinatus L. Groenlandia densa (L.) Fourr.	Droseraceae Aldrovanda vesiculosa L. Brassicaceae Subularia aquatica L.
Ruppiaceae	Callitrichaceae
Ruppia cirrhosa (Petagna) Grande Ruppia maritima L.	Callitriche palustris L. Callitriche cophocarpa Sendtner Callitriche stagnalis Scop. Callitriche platycarpa Kutz.
Zannichelliaceae	Elatinaceae
Zannichellia palustris L.	Elatine alsinastrum L. Elatine triandra Schkuhr. Elatine hydropiper L.
Zosteraceae	Haloragaceae
Zostera marina L. Zostera nana Roth	Myriophyllum spicatum L. Myriophyllum verticillatum L.
Najadaceae	Primulaceae
Najas marina L. Najas minor (All.) Goss. et Germ. Najas graminea Del.	Hottonia palustris L. Lentibulariaceae Utricularia minor L. Utricularia vulgaris L. Utricularia australis R. Br.
2. Neustophytes
Polypodiophyta	Lemnaceae
Salviniaceae	Lemna gibba L. Lemna minor L. Lemna trisulca L. Spirodela polyrhiza (L.) Schleid. Wolffia arrhiza (L.) Horkel
Salvinia natans (L.) All.
Azollaceae
Azolla filiculoides Lam. Azolla caroliniana Willd.	Magnoliophyta
Marsileaceae	Nymphaceae
Marsilea quadrifolia L.	Nuphar lutea (L.) S. et S. Nymphaea alba L.
Magnoliophyta	Trapaceae
Potamogetonaceae	Trapa natans L.
Potamogeton natans L. Potamogeton polygonifolius Pourr. Potamogeton fluitans Roth	Menyanthaceae
Hydrocharitaceae	Nymphoides peltata (S.G. Gmel.) Kuntze
Hydrocharis morsus ranae L.
3. Helophytes
Polypodiophyta	Cyperaceae
Thelypteridaceae	Juncellus serotinus (Rottb.) Clarke Cyperus glaber L. Cyperus longus L. Cyperus glomeratus L. Cyperus rotundus L. Cyperus fuscus L. Eriophorum latifolium Hoppe Eriophorum gracile Koch. Eleocharis palustris (L.) R. et S. Eleocharis quinqueflora (Hartm.) Schwarz Eleocharis uniglumis (Link.) Schult. Isolepis supina (L.) R. Br. Scirpus sylvaticus L. Schoenoplectus mucronatus (L.) Palla Schoenoplectus lacustris (L.) Palla Schoenoplectus tabernaemontanii (Gmel.) Palla Schoenoplectus litoralis (Schrad.) Palla Schoenoplectus triqueter (L.) Palla Bolboschoenus maritimus (L.) Palla Schoenus ferrugineus L. Cladium mariscus (L.) R. Br. Carex disticha Huds. Carex paniculata L. Carex buekii Wimm. Carex acuta L. Carex gracilis Curt. Carex distans L. Carex pseudocyperus L. Carex riparia Curt. Carex acutiformis Ehrh. Carex stellulata Good. Carex vesicaria L. Carex limosa L.
Thelypteris palustris Schott
Magnoliophyta
Typhaceae
Typha latifolia L. Typha angustifolia L. Typha schutlewortii Koch et Sonder Typha laxmannii Lepech. Typha australis Schum. et Thonn.
Sparganiaceae
Sparganium erectum L. Sparganium neglectum Beery Sparganium angustifolium Michx. Sparganium minimum Wallr. Sparganium emersum Rehm.
Alismataceae
Alisma gramineum Lej. Alisma plantago-aquatica L. Alisma lanceolatum With. Sagittaria sagittifolia L. Sagittaria latifolia Willd. Caldesia parnassifolia (Bassi) Parl.
Butomaceae
Butomus umbellatus L.
Hydrocharitaceae	Rosaceae
Stratiotes aloides L.	Potentilla palustris (L.) Scop.
Poaceae	Fabaceae
Leersia oryzoides (L.) Sw. Digraphis arundinaceae (L.) Trin. Calamagrostis lanceolata Roth. Beckmannia eruciformis (L.) Host. Phragmites australis (Cav.) Trin. Glyceria aquatica Wahlenb. Glyceria plicata Fries Glyceria fluitans R. Br.	Lathyrus palustris L.
Araceae	Violaceae
Acorus calamus L.	Viola palustris L.
Juncaceae	Lythraceae
Juncus maritimus Lam. Juncus subnodosus Schrk. Juncus articulatus L. Juncus thomasii Ten.	Lythrum salicaria L.
Amaryllidaceae	Apiaceae
Leucojum aestivum L.	Cicuta virosa L. Sium latifolium L. Sium lancifolium Reib. Berula erecta (Huds.) Coville Oenanthe aquatica (L.) Poir. Oenanthe fistulosa L. Oenanthe banatica Heuff. Oenanthe silaifolia Bieb. Oenanthe stenoloba Schur. Peucedanum palustre (L.) Moench.
Iridaceae
Iris pseudacorus L. Gladiolus palustris Gaud.
Orchidaceae
Orchis cordigera Fries Gymnadenia frivaldskyana Hampe Epipactis palustris (L.) Crantz Liparis loeselii (L.) Rich.
Salicaceae	Primulaceae
Salix rosmarinifolia L.	Primula farinosa L. Primula deorum Vel. Samolus valerandii L. Lysimachia nummularia L. Lysimachia thyrsiflora L. Lysimachia vulgaris L.
Polygonaceae
Rumex hydrolapathum Huds. Rumex palustris L. Persicaria amphibia (L.) S.F. Gray Persicaria minor (Huds.) Opiz Persicaria hydropiper Opiz Persicaria lapatifolia (L.) S.F. Gray Persicaria maculata (Raf.) S.F. Gray
Caryophyllaceae	Gentianaceae
Myosoton aquaticum (L.) Moench Silene asterias Griseb.	Gentiana nivalis L.
Ranunculaceae	Menyanthaceae
Caltha polypetala Hochst. Caltha palustris L. Caltha cornuta Schot. Ranunculus pseudofluitans (Syme) Newb. Ranunculus spaerospermus Boiss. et Blanche Ranunculus lingua L. Ranunculus circinatus Sibth. Ranunculus sceleratus L.	Menyanthes trifoliata L.
	Lamiaceae
	Mentha aquatica L.
	Scrophulariaceae
	Pedicularis palustris L. Scrophularia alata Gilib.
Droseraceae
Drosera rotundifolia L.	Asteraceae
Brassicaceae	Eupatorium canabinum L. Aster tripolium L. Pulicaria dysenterica (L.) Cass. Petasites kablikianus Tausch. Petasites officinalis (L.) Gaertn. Petasites albus (L.) Gaertn. Senecio paludosus L. Leontodon riloensis Hayek Sonchus palustris L.
Cardamine rivularis Schur. Cardamine amara L. Nasturtuim officinale L.

Table 8. Species of Hydatophytes, Neustophytes, and Helophytes Recommended for Protection

Potamogeton praelongus Wulfen	Caltha polypetala Hochst. et Lorent.
Potamogeton trichoides Cham. et Schlecht.	Ranunculus circinatus Sibth.
Zostera nana Roth.	Ceratophyllum muricatum Cham.
Najas graminea Del.	Lysimachia thyrsiflora L.
Calamagrostis lanceolata Roth.	Pedicularis palustris L.
Schoenus ferrugineus L.	Utricularia neglecta Lehmann.
Acorus calamus L.	Sonchus palustris L.

Table 9. Biodiversity in Bulgaria: Lichens

Order	Family	Genus	Species
Arthoniales	5	5	16
Dothidiales	1	4	15
Verrucariales	1	8	53
Pyrenulales	4	5	11
Caliciales	3	10	19
Ostropales	1	2	7
Graphidales	2	3	5
Lecanorales	26	101	564
Lichenes Imperfecti	3	3	7
Families of unclear systematic state	5	6	12
Total	51	147	709

Table 10. Rare Species of Lichens in Bulgaria

Staurothele bacilifera Arn.	Solorina bispora Nyl.
Microglaena modesta (Nyl.) Smith.	Nephroma lusitanicum Schaer.
Normandina pulchella (Borr.) Nyl.	Peltigera lepidophora (Nyl.) Vain.
Stenocybe pullatula (Ach.) Stein.	Lecidea lucida Ach.
Cyphelium tigillare Ach.	Catinaria laureri (Hepp.) Degel
Sphaerophorus globosus (Huds.) Vain.	Icmadophila ericetorum (L.) A.Z.
Thyrea pulvinata (Schaer.) Mass.	Lecania nylanderiana Mass.
Peccania coralloides Mass.	Phlyctis agelaea (Ach.) Fw.
Leptogium cyanescens (Hoffm.) Koerb.	Parmelia trichotera Hue
Heppia ruinicola Nyl.	Allectoria pellucida Mot.
Massalongia carnosa (Dicks.) Koerb.	Usnea longissima Ach.
Lobaria linita (Ach.) Rabh.	Heterodermia speciosa (Wulf.) Trev.
Sticta sylvatica (Huds.) Ach.

Table 11. Endemic Taxa of Lichens in Bulgaria

Verrucaria bulgaria Szat.	Lecidea macrocarpa f. microcarpa Szat.
Collema rhodopense Szat.	Lecidea incongrua f. ochracea Szat.
Acarospora bulgaria H. Magn. et Szat.	Aspicilia cinerea f. ochraceoferruginea Szat.
Pertusaria Kasandjeffii Szat.	Aspicilia cinerea f. olivaceoatra Szat.
Alectoria degennii Szat.	Aspicilia cinerea f. corticola Szat.
Alectoria pellucida Mot.	Physcia aipolia f. nikoloffii Gyel.
Parmelia pulla f. bulgaria Gyel.	Physcia stellaris f. viridescens Gyel. et Nik.y

Bibliography

Algae

Aleksieva G. 1957. "Artenzusammensetzung und jahreszeitliche Dynamik des Phytoplanktons in den Reisfeldern bei Plovdiv." Naucn. trud. VSSI, Plovdiv, 4:351-369.

Aleksieva G. 1960. "Arten Bodenalgen in manchen Bodentypen ostlich von Plovdiv." Naucn. trud. VSSI, Plovdiv, 8:81-92.

Aleksieva G. 1965. "Verwendung einiger mechanischer und chemischer Mittel gegen die Algen in der Reisfeldern." Naucn. trud. VSSI, Plovdiv, 14, 1:171-177.

Angelov A. 1956. "Hydrologische und hydrobiologische Untersuchungen uber den Rabischa-See." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 49, 1:1-30.

Angelov A. 1964. "Sanitarbiologische Analyse des Trinkwasser der Stadt Sofia von der Rila-Wasserleitung." Annuaire de l'universite de Sofia, Faculte de biologie, geology et geography, 57, 1:191-215.

Angelov A. 1968. "Prognose fur die Entwicklung biologischer Prozess beim neuprojektierte Stausses Jasna Poljana-Bezirk Burgas." Annuaire de l'Universite de Sofia, Faculte de biologie, 61, 1:73-80.

Arnaudov V. 1936. "Petrographisch-bodenkundliche Untersuchungen in des Becken von Simitliu-Serbinovo und der Umgebung derselben /Bezirk von Gorna Djumaja." Travaux de la Societe bulgare des Sciences naturelles, 17:25-70.

Bourrely P. 1965. "Note de nomenclature algae: Valkanoviella nov. nom." Revue Algol., 8, 1:64-65.

Celan M., A.Bavaru. 1967. "Contribution a la connaissance des algues rouges `Rhodophyceae' de la mer Noire." Revue Roumaine Biol., Ser. Bot., 12, 5:345-362.

Czapic A. 1952. "Unterzuchungen uber die Lithotelmen der Bulgarien Schwarz-Meerkuste." Trud. Morsk. -biol. st., 17:73-82.

Delceva R. 1965. "On the study of the soil Protozoa in Bulgaria." Bulletin de l'Institut de Zoology, 18:199-223.

Dimitrov M., Z. Ljudskanova. 1967. "Feeds and feeding correlation of commercial fish in the G.Dimitrov dam." Proceedings of the research institute of fisheries and oceanography, Varna, 8:339-358.

Dimitrova M., M. Nikolova. 1968. "Saprobiological characteristics of the river Tundza." Hidrotechn. ....., 13, 10:309-311.

Dimitrova S. 1969. "Contribution to the benthic algal flora of the Bulgarian Black Sea littoral. I." Mitteilungen des Botanischen Instituts, 19:147-159.

Dimitrova-Konaklieva S. 1969. "New sea algae from the Bulgarian Black-Sea coast." Second national conference on botany, p. 139-143.

Dimitrova-Konaklieva S. 1973. "Algae pro macrophytobentho marino Bulgariae /sinus Achtopolitanus/ novae." Novitates systematice plantarum non vascularium, 10:71-73.

Dimitrova-Konaklieva S. 1974. "New seaweeds for the Black Sea and bulgarian coast found in the Ahtopol bay." Probl. farm., 2:63-69.

Dimitrova-Konaklieva S. 1981. "Geographical analysis of the marine algae of the Black-Sea in the Ahtopol area." Phytology, 18:22-35.

Dimitrova-Konaklieva S. 1983. "Marine macrobenthic algae of Bulgaria - studies and possibilities for their use." Jubilee scientific conference 90 years acad. D. Jordanov, Omurtag, p. 112-119.

Dimitrova-Konaklieva S. 1984. "Peculiarities of the seaweeds development from Ahtopol's district in dependence of seasons and ecoconditions." Modern theoretical aspects of plant ecology, p. 313-325.

Dimitrova-Konaklieva S. 1987. "How many are marine macrobenthic algae in Bulgaria?." Bulletin of the national oceanographic committee, 3:17-22.

Dimitrova-Konaklieva S. 1987. "Comparison between bulgarian microalgic flora with these from the other Black Sea regions." Proceedings IVth national conference-Botany, p. 148-155.

Dimov I. 1960. "Le zooplancton de la mer Noire devant la cote bulgare pendant les annees 1954, 1955 et 1956." Naucn. trud. NIRRP- Varna, 2:85-147.

Draganov S. 1960. "Beitrag zur Algenflora Bulgariens." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 52, 1:163-166.

Draganov S. 1964. "Untersuchungen uber die Algen-flora der Boden Bulgariens. I. Zsammensetzung und Verbreitung der Blaualgen in der Tschernosem-Smolnitza des sofioter Beckens." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 57, 1:111-123.

Draganov S. 1964. "Beitrag zur Algenflora Bulgariens.II" Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 57, 1:9-16.

Draganov S. 1964. "Cylindrospermum echinulatus sp. nov. eine neue Blaualge." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 57, 1:35-39.

Draganov S. 1965. "Untersuchungen uber die Algen-flora der Boden Bulgariens. II. Verbreitung von Nostoc commune Vauch. auf Bodentypen." Annuaire de l'Universite de Sofia, Faculte de biologie, 58, 2:123-129.

Draganov S., A. Viceva. 1966. "Boden-Blaualgen aus dem botanischen Garten der Sofioter Universitat." Annuaire de l'Universite de Sofia, Faculte de biologie, 59, 2:27-34.

Draganov S., E. Genova. 1966. "Untersuchungen uber die Algenflora der Boden Bulgariens. III. Vertical Verbreitung der Blaualgen an den Nordabhengen des Vitoschagebirge." Annuaire de l'Universite de Sofia, Faculte de biologie, 59, 2:153-163.

Draganov S. 1968. "On the composition and distribution of the blue-green algae in the principal soil types of Bulgaria." Materials of the 6th coordinated conference and scientific symposium on theme VI.5.5. RGM, Sofia, p. 1-5.

Draganov S. 1968. "Cylindrospermum dobrudjense nom. nov." Annuaire de l'Universite de Sofia, Faculte de biologie, 61, 2:43-44.

Draganov S., E. Dimova. 1971. "Untersuchungen uber Bestand und Menge von Algen in lange Zeit luftrocken aufbewahrten Bodenproben." Annuaire de l'Universite de Sofia, 63, 2:55-64.

Draganov S., T. Mechinev. 1971. "Untersuchungen uber Algenbestand und Verbreitung in den Halden des Industriekomplex Mariza-Istok." Annuaire de l'Universite de Sofia, 63, 2:65-73.

Draganov S. 1977. "Die Nostoc-Scytonema-Zoenose in Bulgarien." Annuaire de l'Universite de Sofia, 68, 2:31-34.

Draganov S., E. Dimitrova-Burin. 1980. "Speleo-algological studies in Bulgaria." Ecology, 6:62-69.

Draganov S. 1981. "Aulosira valkanovii sp. n. and Calothrix hollerbachii sp.n.- New hormogonal blue-green algae from soil in Bulgaria." Phytology, 18:52-56.

Draganov S. 1984. "Uber die Methoden zur Feststellung der Algenmengen im Boden." Annuaire de l'Uni-versite de Sofia, Faculte de biologie, 2:64-72.

Draganov S., B. Georgiev, E. Mileva, I. Georgieva. 1984. "Blue-green algae of the northern and central parts of the bulgarian Black sea coast." Hydrobiology, 20:51-64.

Draganov S., M. Stoyneva, B.Georgiev. 1987. "The algal flora in the Bulgarian section of the Danube and adherent basins." Symposium "The significance of the wet zones for the preservation of the genetic funds 8-12 Oct., Srebarna, Sofia, p. 42-51.

Draganov S., M. Stoyneva. 1988. "Algal flora of river Danube (Bulgarian sector) and adjoined water basins. I. Composition and distribution of the phytoplankton of river Danube." Annuaire de l'Universite de Sofia, Faculte de biologie, 2, 79:38-63.

Draganov S., M. Stoyneva. 1990. "Saprobiologische Beurteilung des Donauwassers im bulgarischen Abschnitt des Stromes in Jahre 1982 wahrend der vier Jahreszeiten 1987/88 aufgrund des Phytoplanktons." Limnol. Berichte der 28. Tagung der IAD, Varna, September, 1990, 349-354.

Draganov S., M. Stoyneva. 1991. "Algal flora of the river Danube (Bulgarian sector) and the adjoined water basins. II. Composition and distribution of the phytobenthos of the river Danube." Annuaire de l'Universite de Sofia, Faculte de Biologie, 2, 80:11-24.

Draganova L. 1968. "Application of algae in pharmacy. I. Algae and its products as medicines." Farmacija, 18, 4:59-66.

Genov M., D.Grancarova, S.Danov. 1960. "Characteristics and influence of slime sediment upon the Studena dam water quality." Sb. trud. NISHI, 5:1-14.

Georgiev S. 1906. "Contribution a l'etude des Diatomes, des Champignons, des Filicinees et des Phanerogames de Bulgarie." Annuaire de l'Universite de Sofia, 2:83-124.

Hindak F. 1978. "The genus Lagerheimia Chod. and Lagerheimia-like unicells in the genus Scenedesmus Meyen (Chlorophyceae)." Biologia, Bratislava, 33, 10:795-808.

Hobatev F., G. Bacvarov. 1969. "Observation de l'influence toxique des substances chimicues de l'industrie papetiere des Algues vertes." Travaux Scientifiques de l'Ecole Normale Superieure, Plovdiv, 7, 1:183-191.

Istvanffi G. 1890. "Algae nonnullae a beato E. Frivalddszky in Rumelia lectae." Termeszetr. Fuz., 13, 2-3:67-77.

Ivanov A. 1965. "Qualitative characteristics of the Black Sea Phytoplankton compound." In: Studies of the Plankton in the Black and Azov Seas, Kiev, p. 17-35.

Ivanov A. 1969. "Uber den Einfluse der Donau auf das Phytoplankton des nordwestlichen Teils des Schwarzen Meers." In: Limnological investigations of the Danube, Kiev, p. 448-455.

Ivanov H. 1912. "Essai d'etude des Flagellates de Bulgarie." Travaux de la Societe bulgare des Sciences naturelles, 5:114-141.

Ivanov L., A. Rozdestvenski, T. Marinov, V. Petrova-Karadjova, A. Konsulov, S. Mitev. 1980. "On the hydrochemical conditions, nutritive base and fish stocks in Mandra dam." Proceedings Institute of Fish Resources, Varna, 18:7-71.

Jordanov D., S. Dimitrova. 1960. "Apport a la connaissance des algues benthoniques au golfe de Baltchik." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 52, 1:171-184.

Josifov M., G. Decev. 1950. "Hydrobiologische Untersuchungen der Rilaseen wahrend des Winters." Annuaire de l'Universite de Sofia, 46, 3:197-199.

Kaneva-Abadzieva V., T. Marinov. 1965. "Fouling organisms along the bulgarian Black Sea coast." Proceedings of the research institute of fisheries and oceanography Varna, 6:137-144.

Kawecka B. 1974. "Vertical distribution of the algae communities in Maljovica stream (Rila-Bulgaria). Pol. Arch. Hydrobiol., 21:211-228.

Kawecka B. 1976. "Eunotia flexuosa (Breb.)Kutz. var. rilensis n.var. (Bacillariophyceae) w potoku Maljovica (Rila-Bulgaria). Acta hydrobiol., 18, 4:425-427.

Kirjakov I. 1969. "Studies on Coelastrellaenalax group." Second national conference of Botany, Sofia, p. 67-68.

Kirjakov I. 1970. "Beitrag zur Algenflora Bulgariens. I" Travaux Scientifiques de l'Ecole Normale Superieure, Plovdiv, 8, 3:191-196.

Kirjakov I. 1970. "Beitrag zur Systematik von Centritractus belonophorus Lemm. (Xanthophyta). Natura, 3, 1:131-134.

Kirjakov I. 1971. "Beitrag zur Algenflora Bulgariens II." Travaux Scientifiques de l'Ecole Normale Superieure, Plovdiv, 9, 3:141-147.

Kirjakov I. 1972. "The algal flora of the Smolyan lakes (Chlorococcales)." Mitteilungen des Botanischen Instituts, 22:97-117.

Kirjakov I., E. Paskaleva. 1972. "Das Phytoplankton im Stausee Rosov Kladenetz." Proceedings of the freshwater fishery research station, Plovdiv, 9:119-128.

Kirjakov I. 1974. "Beitrag zur Algenflora Bulgariens. III." Travaux scientifiques Universite de Plovdiv, 12, 4:23-30.

Kirjakov I. 1975. "The genus Siderocelis Fott in Bulgaria distribution and ecology." Phytology, 2:50-53.

Kirjakov I. 1976. "On some morphological features of subgenus Fusodesmus (Chod.) Kiriakov nov. nom. from genus Scenedesmus Meyen (Chlorococcales)." Collected papers of young scientists and students, Plovdiv, 4:197-204.

Kirjakov I. 1978. "Notizzen uber die Scenedesmus-Arten (Chlorococcales) Bulgariens." Travaux scientifiques Universite de Plovdiv, 16, 4:41-55.

Kirjakov I. 1979. "A contribution to the composition and distribution of Chlorococcales (Chlorophyta) in Bulgaria." Travaux scientifiques Universite de Plovdiv, 17, 4:43-56.

Kirjakov I. 1979. "New for the Bulgarian algae flora Volvophyceae (Chlorophyta)." Travaux scientifiques Universite de Plovdiv, 17, 4:27-41.

Kirjakov I. 1980. "On some new Scenedesmus taxa (Chlorophyta, Chlorococcales)." Travaux scientifiques Universite de Plovdiv, 18, 4:61-67.

Kirjakov I. 1981. "Biometrical and morphological research on Sphaeroplea soleirolii (Duby) Mont. var. crassisepta (Reith) Ramanathan (Chlorophyta)." Travaux scientifiques Universite de Plovdiv, 19, 4:85-94.

Kirjakov I.1981. "Chorological date about Euglenophyta in Bulgaria." Travaux scientifiques Universite de Plovdiv, 19, 4:95-107.

Kirjakov I. 1981. "A contribution to the algal flora of Bulgaria. IV." Travaux scientifiques Universite de Plovdiv, 19, 4:108-120.

Kirjakov I. 1981. "A contribution to the algal flora of Bulgaria. V." Travaux scientifiques Universite de Plovdiv, 19, 4:121-140.

Kirjakov I. 1981. "Horn chewing of Scenedesmus Meyen (Chlorococcales, Chlorophyta)." Hydrobiology., Experim. 2 algol., 13:46-56.

Kirjakov I. 1982. "New for the Bulgarian algae flora Ulothrichales (Chlorophyta)." Travaux scientifiques Universite de Plovdiv, 20, 4:67-77.

Kirjakov I., D. Vodenicharov., E. Paskaleva. 1982. "Phytoplankton composition in fish-raising reservoirs near Plovdiv." Hydrobiology, 17:14-29.

Kirjakov I. 1983. "Notes on the Euglenophyta flora and its distribution in Bulgaria." Phytology, 22:46-60.

Kirjakov I. 1983. "On the ecology of genus Scenedesmus Meyen (Chlorophyta, Chlorococcales). I. Abiotical factors of the environment." Ecology, 12:13-22.

Kiriakov I. 1983. "Le genre Strombomonas Deflandre (Euglenophyta) en Bulgarie Cryptogamie." Algologie, 4, 1-2:127-139.

Kirjakov I. 1984. "A contribution to the algal flora of Bulgaria. VI." Travaux scientifiques Universite de Plovdiv, 22, 1:17-24.

Kirjakov I. 1984. "Neue und seltem mitgeteilte Vertreter der Mesoteniaceae, Gonatozygaceae und Desmidiaceae (Zygnemophyta) in der Algenflora Bulgariens." Travaux scientifiques Universite de Plovdiv, 22, 2:88-101.

Kirjakov I., D. Vodenicharov. 1984. Taxonomische Zusammensetzung der Algen in den Smoljan und Cair-Seen /Rhodopen/. I" Travaux scientifiques, Universite de Plovdiv, 22, 2:55-88.

Kirjakov I. 1985. "A contribution to the algal flora of Bulgaria. VII." Travaux scientifiques, Universite de Plovdiv, 23, 1:17-24.

Kirjakov I., D. Vodenicharov. 1986. "The algae in the Cerni Ossam river basin with regard to its saprobiologic state." In: Scientific conference on ecological and genetic problems caused by environment pollution, Vraca, 2:380-383.

Kirjakov I., D. Vodenicharov. 1986. "Die Gattung Tetrastrum Chod. 1885 (Chlorococcales) in den Gewassern Bulgariens." Arch. Hydrobiol., 73, 3:351-363.

Kirjakov I. 1987. "A survey of the euglenoid algae represented in Bulgaria and new data for their distribution." Proceedings fourth national conference of botany, Sofia, 1:116-123.

Kirjakov I. 1987. "Variability of species of the genus Strombomonas Deflandre (Euglenophyta)." Proceedings fourth national conference of botany, 1:124-131.

Kirjakov I., D. Vodenicharov. 1987. "Taxonomische Zusammensetzung der Algen in den Smoljan und Cair-Seen /Rhodopen/. II." Travaux scientifiques Universite de Plovdiv, 25, 6:23-32.

Kirjakov I., D. Vodenicharov. 1987. "Taxonomische Zusammensetzung der Algen in den Smoljan und Cair-Seen /Rhodopen/.III." Travaux scientifiques Universite de Plovdiv, 25, 6:34-45.

Kirjakov I. 1988. "Neue und einimalig mitgetelte Arten der Gattung Spirogyra Link (Zygnemophyta) in der Algenflora Bulgariens." Travaux scientifiques Universite de Plovdiv, 26, 6:23-25.

Kirjakov I., D. Vodenicharov. 1988. "Taxonomische Zusammensetzung der Algen in den Smoljan und Cair-Seen /Rhodopen/.IV." Travaux scientifiques Universite de Plovdiv, 26, 6:29-38.

Kirjakov I. 1989. "A contribution to the algal flora of Bulgaria. VIII." Travaux scientifiques Universite de Plovdiv, 27, 6:30-37.

Kirjakov I., D. Vodenicharov. 1989. "Studies of the variability, taxonomy and ecology of species causing water blossoming. II. Taxonomical and ecological notes on some little known taxa of green flagellate algae." Phytology, 36:3-9.

Kol E. 1956. "Sur la microvegetation de la neige des montagnes de la Bulgaria I: Mont Pirin et mont Rila." Mitteilungen des Botanischen Instituts, 5:377-385.

Komarek J. 1956. "Some interesting blue-green algae from the Bulgarian coast of Black Sea near Bourgas." Acta. Univ. Carolinae, Ser. Biol., 2, 1:91-123.

Konaklieva S. 1970. "Algae marine pro Bulgaria novae et rarae." Novitates systematice plantarum non vascularium, 6:68-72.

Konsulova T., A. Konsulov, S. Moncheva. 1991. "Ecological characteristic of Varna Bay (Black sea) coastal ecosystem under summer "bloom" conditions." Compt. Rend. Academy Bulg. Sci., 44, 8:113-117.

Kocev H., S. Husak, H. Otahelova. 1987. "Materialen zur phytozonologischen Charakteristik der Wasserund Sumpfvegetation in den ostlichen Teilen der Donau in Bulgarien." In: International Symposium, "The significance of the wet zones for the preservation of the genetic funds, 8-12 Oct. 1984, Srebarna, p. 81-99.

Lepsi J. 1925. "Microbiologia cismelelor din Cavarna" An. Gimn. Mixt Cavarna, 1:26-52.

Lepsi J. 1926. "Uber die Protozoenfauna einiger Quellen der Dobrudscha." Arch. Hydrobiol., 17:751-770.

Lepsi J. 1928. "Studii asupra litoralului Sabla-Ecrene." Mem. Sect. Sti. Acad. Romana, Ser. III, 4, 6:205-324.

Lepsi J. 1931. "Despre cateva Rhizopoda si Euflagellate din Marea Neagra." Pescar. Piscicult., 4:5-29.

Ludskanova Z. 1967. "Dynamik der Anzahl und Biomasse des Zooplanktons im Stausee Batak fur die Periode 1963-1965." Proceedings of the research institute of fisheries and oceanography, 8:371-387.

Ludskanova Z. 1969. "Das Plankton des Stausees Pjasatschnik." Bulletin of the test station of freshwater pisciculture, Plovdiv, 6:21-30.

Ludskanova Z. 1971. "Untersuchungen uber das Zooplankton in den Becken des Fischzucht-beitriebs Mecka." Proceedings of the freshwater fishery research station, Plovdiv, 8:13-25.

Ludskanova Z. 1972. "Dynamik von Menge und Biomasse des Zooplanktons im Stausee Ovcarica in den Jahren 1968-1970." Proceedings of the freshwater fishery research station, Plovdiv, 9:73-81.

Makarova, 1969: "The formation and the affinities of the phytoplankton of the Black Sea, Sea of Azov and Caspian Sea." Botn. J., USSR, 54(3): 389-398.

Marasovic, I., T. Pucher-Petkovic and V. Petrova-Karadjova, 1990: "Prorocentrum minimum (Dinophyceae) in the Adriatic and Black Sea." J. Mar. Biol. Ass. U.K., 70.

Markov, V., 1935: "Biochemische Prozesse bei der Moorbildung im Pomorie-/Anchialo/ See." Annuaire de l'Universite de Sofia, 14:445-472.

Markoff, W., 1939: "Biochemischer Prozess bei der Moorbildung im Pomoiasee." Zentralbl. Bacteriol., II(100): 277-288.

Michajlov, W., 1965: "Astasia bulgaria sp. n. and Astasia sophiensis sp. n. Euglenoidina parasitica found in Bulgaria." Acta Parasitol. Polonica, 13(1): 7-17.

Michajlova-Nejkova, M., 1961: "Hydrobiolical research of the Mandra lake with regard to its importance as a fishing ground." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 53(1): 57-122.

Moncheva, S. and C. Konsulova, 1983: "The phytoplankton as a food for the cultured mussel Mytilus galloprovincialis Lam. in the area around the cape Kaliakra, Bulgaria." Proceedings Inst. of Fisheries, Varna, 20:145-152.

Moncheva, S., 1987: "Waterbloom" phenomenon and phytoplankton succession in relation to eutrophication." First national conference on the problems of biological monitoring, Plovdiv, 22-24 Oct., p. 133-138.

Moncheva, S., 1991: "Quantitative development of some phytoplankton species as an indicator of eutrophication along the bulgarian Black Sea coast." Oceanology, S. BAS, 21:21-30.

Moncheva, S., 1991: "On the thermohaline characteristic in the development of some mass phytoplankton species in the northern part of the bulgarian Black Sea coast." Oceanology, S. BAS, 21:14-20.

Moncheva, S., 1992: "Cysts of blooming dinoflagellates from Black Sea." Rapp. Comm. int Mer Medit, 33:261.

Moncheva, S., "Eutrophication, Plankton Blooms /Hypoxia." Report Int. Workshop on the Black Sea: Focus on the Western Black Sea Shelf, Varna, 30 Sept.-4 Oct., IO, BAS, Coast. Res. Ctr., Woods Hole Ocean. Inst. (in print).

Najdenov, V., 1963: "Utersuchungen uber das Zooplankton aus den Teichen der Versuchsstation fur Binnenfischerei und der Staatlichen Teichwirschaft bei Plovdiv." Bulletin de l'Institut de Zoology, 14:165-195.

Najdenov, V., 1964: "Plankton und Dynamik der fuhrenden Planktonformen in Stausee Batak." Bulletin de l'Institut de Zoology, 15:151-183.

Najdenov, V., 1965: "Beitrag zur Erforschung der Copoepoden - und Brachiopodenfauna aus bulgarischen Gewassern an der Donau." Bulletin de l'Institut de Zoology, 19:203-232.

Najdenov, V., 1966: "Verteilung und Dynamik der Zooplanktons in der Donau zwishcen dem 845. und 375. Flusskilometer." Bulletin de l'Institut de Zoology, 20:5-53.

Najdenov, V., 1967: "Hydrobiologische Untersuchungen der Wasserbecken an der sudlichen Schwarzmeerkuste und im Strandza-Gebirge. I.- Cladocera, Calanoida, Cyclopoda." Bulletin de l'Institut de Zoology, 24:57-95.

Najdenov, V., "Uber die Hydrofauna der bulgarischen Donauinselsumpfe.: In: LimnologischeBerichte der X. Jubilaumstagung der Arbetsgemeinschaft Donauforschung /Bulgarien 10-20. Okt. 1966/, Sofia, pp. 233-246.

Najdenov, V., 1969: "Formierung der Zooplanktonzonosen in den Stauseen Bulgariens." In: Limnological investigations of the Danube, Kiev, p. 279-285.

Najdenov, V., 1973: "Bioxonologische Untersuchungen stehender Gewasser des Ludogorie." Bulletin de l'Institut de Zoology, 38:149-181.

Najdenov, V. and D. Sais, 1977: "Einflus des Planktons im Stausee Rozov Kladenec auf Filtrationseffekivitat einiger Mikrosiede." Hydrobiology, 5:38-51.

Najdenov, V. and D. Sais, 1977: "Das Plankton im Stauraum Dospat in den ersten nach der Aufspeicherung." Hydrobiology, 5:24-37.

Najdenov, V. and D. Sais, 1985: "Der Einflub der Abwasser aus dem Bebeit von Fusse/Bulgarien/ auf die Entwicklung des Donauplanktons." In: Die Auswirckung der wasserbaulichen Mabnahmen un der Belastung auf das Plankton und das Benthos der Donau, Verlag der BAW, Sofia, pp 103-113.

Paskaleva, E., 1975: "Entwicklung des Phytoplanktons in Karpfenzuchtteichen bei Anzucht von Polykulur." Proceedings of the freshwater fisher research station, Plovdiv, 11:17-28.

Paspalev, G., 1933: "Hydrobiologische Untersuchungen uber den Golf von Varna." Trud. Cernom. biol. st., 2:1-18.

Paspalev, G., 1935: "Hydrobiologische Untersuchungen uber den Golf von Varna. II. Schiffsboden Bewachsung." Trud. Cernom. biol. st., 4:1-10.

Paspalev, G., 1942: "Beitrag zur Erforschung des Varna Golfs und Varna Sees." Trud. Cernom. biol. st., 10-11:49-144.

Petlov, S., 1898: "Ein Beitrag zur Untersuchungen der bulgarischen einzelligen Suswassergrunalgen, die im Pilagebirge, Kostenski-Gebirge /Rhodopen/, Vitoscha Gebirge, Moor von Gragoman und um Sofia vorkommen." Period. Sp. Bulg. Kniz. D-vo, 57:111-135.

Petkov, S., 1898: "Ein Beitrag zur Untersuchungen der bulgarischen einzelligen Suswassergrunalgen, die im Rilagebirge, Kostenski-Gebirge /Rhodopen/, Vitoscha Gebirge, Moor von Dragoman und um Sofia vorkommen." Period. Sp. Bulg. Kniz. D-vo, 59:791-806.

Petkov, S., 1900: "Deusieme contribution a l'etude des algues d'eau douce en Bulgarie." Travaux de la Societe bulgare des Sciences naturelles, 1:1-21.

Petkov, S., "Troisieme contribution a l'etude des algues d'eau douce de Bulgarie." Period. Sp. Bulg. Kniz. D-vo, 65:385-416.

Petkov, S., 1905: "Contribution supplementaire a la flore algologique de Rilaplanina." Period. Sp. Bulg. Kniz. D-vo, 66:222-239.

Petkov, S., 1905: "Quelques algues marines et saumaitres sur le littoral de la Mer Noire, depuis Atliman jusqu'a Douran-Koulak." Annuaire de l'Universite de Sofia, 1:168-180.

Petkov, S., 1905: Quelques algues marines et saumaitres sur le littoral de la Mer Noire depuis Atliman jusqu'a Douran-Koulak." First conference of medics and natural scientists at Beograd, II:171-173.

Petkov, S., 1906: "Cinquieme contribution a l'etude des Algues d'eau douce de Bulgarie." Nuova Notar., 17:151-161.

Petkov, S., 1906: "Sur la flore algologique d'eau douce de Bulgarie." In: Conger. Int. Bot. II/ Vienne/ Travaux Sci., 354-369 / lena/.

Petkov, S., 1907: "Quatrieme contribution a l'etude des algues d'eau douce de Bulgarie." Sb. nar. umotv., 22/23(3): 1-23.

Petkov, S., 1908: "Cinqueme contribution a l'etude des algues d'eau douce de Bulgarie." Period. Sp. Bulg. Kniz. D-vo, 68:603-624.

Petkov, S., 1910: "Les algues de la Bulgarie du SO et leur dispersion." Annuaire de l'Universite de Sofia, 5(3): 1-88.

Petkov, S., 1991: "La rive danubienne basse et maregageuse de Bulgarie." Letop. Bulg. Kniz. D-vo, 11:72-103.

Petkov, S., 1911: "Contribution supplementaire a l'etude des algues du sommet Kom et ses environs." Annuaire de l'Universite de Sofia, 6:1-15.

Petkov, S., 1911: "Recherches preliminaries concernant la flore des etangs sur la rive bulgare du Danube." Annuaire de l'Universite de Sofia, 6(2): 3-45.

Petkov, S., 1913: "Les Characees de Bulgarie." Revue de l'Academie Bulgarie des sciences, 7:1-44.

Petkov, S., 1914: "Les Characees de Bulgarie." Nuova Notar. 25:35-36.

Petkov, S., 1919: "Materiaux pour la foure algologique du littoral bulgare de la Mer Noire." Revue de l'Academie Bulgarie des sciences, 17:25-134.

Petkov, S., 1922: "La vegetation des eaux de Vitosha. Contribution a l'hydrologie et l'hygiene de la capital." Annuaire de l'Universite de Sofia, 18:1-272.

Petkov, S., 1925: "La flore algologique du mont Pirin planina." Revue de l'Academie Bulgarie des sciences, 20:1-128.

Petkov, S., 1926: "Sur la dispersion horizontale et verticale de certains groups d'organismes thallophytes en Bulgarie." Compt. Rend. I. Congress Geograph. Ethnogr. Slaves, Praha, p. 207.

Petkov, S., 1928: "Note supplementaire de la Flore algologiques du mont Vitosha et ses environs." Bulletin de la Societe botanique de Bulgarie, 2:93-96.

Petkov, S., 1929: "Un habitat algologique important et son changement partiel defavorable." Travaux de la Societe bulgare des Sciences naturelles, 14:99-105.

Petkov, S., 1929: "Brief characteristics of the lower plants from the town of Lovec and its environs." In Lovec and Lovec district, Sofia, 1:43-52.

Petkov, S., 1929: "Quelques especes nouvelles et caracteristiques pour la flore algologique du mont Pirin." Bulletin de la Societe botanique de Bulgarie, 3:29-41.

Petkov, S., 1931: "Note supplementaire a la Fore algologique d'eau douce sur le cotes Bulgares de la Mer Noire." Bulletin de la Societe botanique de Bulgarie, 4:103-115.

Petkov, S., 1932: "Notes sur la flore algologique du village de Geravna et ses environs." Bulletin de la Societe bulgarie des Sciences naturelles, 15-16:11-23.

Petkov, S., 1932: "Sur la flore algologique des cotes bulgares de la Mer Noire." Bulletin de la Societe botanique de Bulgarie, 5:117-127.

Petkov, S., 1933: "La vegetation des sources d'eau douce potablee dans la ville de Lovec et ses environs." Bulletin de la Societe geographique de Bulgarie, 1:277-286.

Petkov, S., 1934: "Deux genres nouveaux pour la flore algologique de Bulgarie." Bulletin de la Societe botanique de Bulgarie, 6:117-120.

Petkov, S., 1934: "Contribution supplementaire aux Characees de Bulgarie." Review de l'Academie Bulgarie des sciences, 51:1-67.

Petkov, S., 1935: "Les Zygnemales de la Bulgarie et leur dispersion." Annuaire de l'Universite de Sofia, 31(3):1-13.

Petkov, S., 1936: "Repartion topographique des Characees en Bulgarie." Compt. Rend. IV Congress Ethnographique Slave, Sofia, p. 131-136.

Petkov, S., 1936: "Sur la dispersion de certains groupes d'organismes thallophytes en Bulgarie et leur provenance primordiale." La Bulagarie devant le IV Congr. Geogr. Ethogr. Slave, Sofia, p. 48-51.

Petkov, S., 1938: "La flore aquatique et le dessechement la plaine marecageuse entre le lac de Devna et le village de Soultanlar et leur importance pour celle--ci." Revue de l'Academie Bulgarie des sciences, 57:43-86.

Petkov, S., 1939: "Notes sur la flore du parc de Madara et sa grotte." Travaux de la Societe bulgare des Sciences naturelles, 28:91-103.

Petkov, S., 1939: "Studies on the lower flora (thallophytes and mosses) from Bulgaria during the last 50 years." Bulletin de la Societe botanique de Bulgarie, 8:19-34.

Petkov, S., 1939: "La vegetation des eaux de Rila au point de vue biologique. Contribution supplementaire a l'hydrologie et l'hygiene de la capital bulgare." Revue de l'Academie Bulgarie des sciences, 59:1-82.

Petkov, S., 1939: "L'etude des grottes en Bulgarie au point de vue de leur flore." Sb. na sajus sa sast. na rodn. prir., 2:101-104.

Petkov, S., 1942: "Note sur une forme particuliere d'Ulothix zonata Kutx. var.valida (Naeg.) Rabenh. ne formant que des hypnospores." Revue de l'Academie Bulgarie des sciences, 65:131-137.

Petkov, S., 1942: "Note concernant les formes de l'espece Thorea ramossissima Bory trouvees en Bulgarie." Revue de l'Academie Bulgarie des sciences, 65:141-144.

Petkov, S., 1943: "La flore des grottes souterraines, des grottes ouvertes et de leurs etangs environnants dans certaines regions calcares de Bulgarie." Revue de l'Academie Bulgarie des sciences, 67:109-188.

Petkov, S., 1943: "Encore quelques especes d'Algues d'eau douce, marine et saumatre apparenant a la flore algologique des Cotes bulgares de la Mer Noire." Bulletin de la Societe botanique de Bulgarie, 9:52-56.

Petkov, S., 1950: "La flore algologique des valles autour du mont Pirin et leurs sources thermales." Mitteilungen des Botanischen Instituts, 1:441-451.

Petkov, S., 1950: "Contribution supplementaire a la flore algologique des Rhodopes." Mitteilungen des Botanischen Instituts, 1:452-473.

Petrova, V., 1957: "Die Plankton Dinoflagellaten der Bulgarischen Schwarz-Meer Kuste." Naucn. trud. NIRP-Varna, 1:113-141.

Petrova, V., 1959: "Beitrag zur Untersuchungen des Phytoplankton im Nordwetlichen Teil des Schwarzen Meers." Compt. Rend. Acad. Bulgare Sci., 12(5): 431-434.

Petrova, V., 1960: "Quantitatschwankungen und "Bluhen" von Rhizosolenia calcar avis Schul. im Schwarzmeer vor der Bulgarischen Kuste in den Jahren 1954-1956." Naucn. trud. NIRP-Varna, 2:73-83.

Petrova, V., 1960: "Zusammensetzung und mengemmassige Vereilung des Phytoplanktons in der Bucht von Varna." Mitteilungen des Botanischen Instituts, 7:247-277.

Petrova, V., 1961: "Le phytoplankton du lac de Varna." Arbeiten des zentralen Forschungstitutes fur Fischzucht und Ficherei, Varna, 1: 184-219.

Petrova, V., 1962: "Blossoming of Prymnesium parvum Crter in the Varna lakes during the summer of 1959." Arbeiten des zentralen Forschungsinstitutes fur Fischzucht und Fischerei, Varna, 2:55-65.

Petrova, V., 1963: "The phytoplankton along the bulgarian coast of the Black Sea during the 1954-1957 period." Arbeiten des zentralen Forschungsinstitutes fur Fischzucht und Fischerei,Varna, 3:31-60.

Petrova, V. and H. Skolka, 1963: "Mass development of the species Nitzschia seriata Cl. in the Black Sea in 1959." Rev. Romaine Biol., Ser. Bot. 9(1):51-65.

Petrova, V. 1964: "Day and night changes of the phytoplankton in the Black Sea along the Bulgarian coast." Proceedings of the Institute of fisheries, Varna, 4:5-23.

Petrova, V. 1964: "Le phytoplancton au large des cotes bulgares de la Mer Noire pendant la periode 1958-1960." Proceedings Institute of fisheries, Varna, 5:5-32.

Petrova, V. and H. Skolka, 1964: Dezvolatea masiva a specici Nitzschia seriata Cl. in apele Marii Negre." Stud. Cercet. Biol., Ser. Bot., 16(1): 47-60.

Petrova, V., 1965: "Besonderheiten in der Entwicklung des Phytoplanktons im Schwarzen Meer vor der bulgarische Kuste in Jahre 1961-1963." Proceedings of the research institute of fisheries and oceanography, Varna, 6:63-74.

Petrova, V., 1965: "Sur le phytoplancton de la Mer Noire devant le littoral bulgare." Rapp. Proc. Verb. Reun., 18(2): 357-361.

Petrova, V., 1966: "Le phytoplancton et les zones littorales de la moitie occidentale de la Mer Noire de 1958 a 1960." Proceedings of the research institute of fisheries oceanography, Varna, 7:29-43.

Petrova, V., 1967: "Dinamique saisonniere et annuele du phytoplancton dans les lace du littoral bulgare ayant une importance economique de peche." Proceedings of the research institute of fisheries, Varna, 8:131-155.

Petrova, V., 1968: "Phytoplankton- da Grundnahrungsglied mit fischwirtschaftlicher Bedeutung in den bulgarische Meeresstrandseen", Ribno. stop., 15(4): 5-8.

Petrova, V., 1968: "Conditions regissant le development du phyloplancton sur le littoral bulgare de la Mer Noire." Rapp. Proc. Verb. Reun., 19(3): 583-585.

Petrova, V., 1971: "Uber die Saison- und Yahres dynamik des Phytoplanckton im Schwarzen Meer vor der bulgarischen Kuste." Talassia Yugoslavica, 7(1): 295-300.

Petrova-Karadzova, V., 1973: "Dynamics of the biomass of the phytoplankton of the Black Sea of the Bulgarian coast during the period of 1964-1970." Research Institute of oceanography and fisheries, 12:41-66.

Petrova-Karadzova, V., 1974: "On the dynamics of phytoplankton in Bourgas lake and in Mandra dam." Research Institute of oceanography and fisheries, 13:35-50.

Petrova-Karadzova, V., 1984: "Changes in planktonic flora in Bulgarian Black Sea waters under the influence of eutrophication." Proceedings Institute of fisheries, Varna, 21:105-112.

Petrova-Karadzova, V., 1985: "Red tide of Prorocentrum micans and Exuviaella cordata in Varna bay and along the coast in November 11984." Hydrobiology, 26:70-78.

Petrova-Karadzova, V., 1987: "Monitoring of the dynamics and the structural variations of the phytoplankton of bulgarian Black Sea waters." First national conference on the problems of biological monitoring, Plovdiv, 22-24 Oct., p. 139-143.

Petrova-Karadzova, V., 1990: "Monitoring the blooms along the bulgarian Black Sea coast." Rapp. comm. int. Mer Medit, 31(1): 209.

Petrova-Karadzova, V. and D. Temniskova-Topalova, 1993: "Dynamik Dichte der Benthos-Diatomeen im bulgarischen Schwarz-meer-schelf." Algologija, AN Ukr., in print.

Rieth, A., 1968: "Beitrage zur Kenntnis der Vaucheriaceen XII. Vaucheria undulata Jao 1936 in Europa." Arch. Protistenk., 110(4): 452-461.

Roubal, J., 1949: "The Desmidiaceae of the Pirin planina of High-Mountain Region in Bulgaria." Stub. Bot., Czechoslovakia, 8(1): 1-68.

Sais, D., 1977: "Die jahreszeitliche Dynamik Phytoplanktons im Sauraum Batak." Hydrobiology, 5:52-61.

Sais, D., 1978: "Compound, distribution and seasonal dynamics of the phytoplankton in the Bulgarian section of the Danube." In: Limnology of the Bulgarian section of the Danube, Sofia, p. 99-118.

Sachev, G. and A. Angelov, 1958: Untersuchungen uber den Bourgas-See/Waja/ in Beziehung zur Verbesserung seiner fischwirtschaftlichen Ausbeutung." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 51(1): 161-210.

Savov, V., S. Dimitrova-Konaklieva, V. Kocev and M. Konaklieva, 1987: "Moglichkeiten der Benutzung des Meeres-Makrophytobenthos zum Zweck des Biomonitoring." First national conference on the problems of biological monitoring, Plovdiv, 22-24 Oct. p. 144-149.

Semerdziev, M., N. Nikiforov, D. Porfirov, I. Kirjakov and O. Nikolova, 1980: "Botanical characteristics and medicinal properties of the algal community in mineral water of Haskovo." First scientific-practical conference, Haskovo Bathing place, Haskovo, p. 135-142.

Sinova, L. and S. Dimitrova-Konaklieva, 1981: "Algae in sinu Achtopolitano (Bulgaria austro-orientalis) invantae." Novitates systematicae plantarum non vascularium, 18:16-21.

Starmach, K., 1964: "Algae on damp coastal rock at Var-na (Bulgaria)." Acta Hydrobil., 6(3): 159-170.

Starmach, K., 1969: "Algae of seaside pools near the mouth of the river Batova in Bulgaria." Fragm. Florist. Geobot., 15(4): 513-521.

Stoyneav, M. and S. Draganov, 1987: "Spring /1987/ phytoplankton in the bulgarian sector of river Danube. II. Species composition. " First national conference on the problems of biological monitoring, Plovdiv, 22-24. okt., p. 121-126.

Stoyneva, M. and S. Draganov, 1987: "Spring /1987/ phytoplankton in the bulgarian sector of river Danube. II. Frequency, floristic similarity and indicators of species." First national conference on the problems of biological monitoring, Plovdiv, 22-24 okt., p. 127-132.

Stoyneva, M., 1988: "The summer /1987/ phyto-benthos in the Bulgarian section of river Danube. Occurring species and indicative species." National scientific conference of young scientists "Ecology and environmental protection", Nov., Plovdiv, p. 17-19.

Stoyneva, M. and S. Draganov, 1991: Saprobiologi-sche Beurteilung des Donauwasser Aufgrund des Fruhlings phytoplankton/1990/." Limnol. Berichte der 29. Arbeitstagung der IAD, Kiev, September, p. 263-266.

Stoyneva, M. and S. Draganov, 1991; "Green algae in the phytoplankton of the Danube /Bulgarian sector /-species composition, distribution, cell numbers and biomass." Arch. Protistenkd., 139:243-260.

Studl, K., 1937: Chemisch-biologische Untersuchungen im Bebiete von Warna, Bulgarien." Ann. Hydrogr. Marti. Meteorol., 65(7): 322-330.

Szemes, G., 1967: "Das Phytobenthos der Donau." In Liepolt R./I Irsg./, Limnologie der Danau, 3:225-241, Stuttgart.

Szemes, G., 1967: "Das Phytoplankton der Donau." In Liepolt R./I Irsg./, Limnologie der Danau, 3:158-179, Stuttgart.

Szemes, G., 1967: " Systematisches Verzeichnis der Pflanzenwelt der Donau mit einer Zusammenfassenden Erlauterung." In Liepolt R./I Irsg./, Limnologie der Danau, 3:225-241, Stuttgart.

Temniskova, D., 1959: "Algenflora und Pfalnzenwelt der Flusse Iskar und Palakaria im Gebiet des Stausee Stalin." Izvest. stud. naucn. D-vo, Sofia, p. 213-248.

Temniskova-Topalova, D., 1963: "Uber die Flora der Euglenophyta und Volvocinae in Bulgarien." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 56(1): 57-66.

Temniskova-Topalova, D., 1965: "Uber die Flora der Euglenophyta und Volvocinae in Bulgarien. II." Annuaire de l'Universite de Sofia, Faculte de biologie, 58(2): 49-58.

Temniskova-Topalova, D., 1966: "Uber die Flora der Euglenophyta und Volvocinae in Bulgarien.III." Annuaire de l'Universite de Sofia, Faculte de biologie, 59(2): 43-57.

Temniskova-Topalova, D. and M. Petrova, 1967: "Die Euglenien in den Reisfeidern um Plovdiv." Annuaire de l'Universite de Sofia, Faculte de biologie, 60(2): 27-56.

Temniskova, D., 1968: "The Euglenic algae in some ephemere water basins in Bulgaria." Materials of the 6th coord. conference and scientific symposium on theme VI.5.5. RGM, Sofia, p. 1-13.

Temniskova-Topalova, D., 1968: "Die Eugleien in temporaren Wasserbecken in der Sofioter Ebende." Annuaire de l'Universite de Sofia, Faculte de biologie, 61(2): 13-42.

Temniskova-Topalova, D., 1969: "Uber die Flora von Euglenophyta und Volvophyceae in Bulgarien. IV." Annuaire de l'Universite de Sofia, Faculte de biologie, 62(2): 1-9.

Temniskova-Topalova, D., 1975: "Uber die Flora von Euglenophyta und Volvophyceae in Bulgarien. V." Phytology, 2:59.

59. Temniskova-Topalova, D., 1977: "New blue-green and green algae in the flora of Bulgaria." Annuaire de l'Universite de Sofia, 2:35-39.

Temniskova-Topalova, D. and N. Misaleva, 1982: "Diatoms from the Bulgarian part of the Ograzhden mountain." Phytology, 20:50-64.

Temniskova-Topalova, D., V. Petrova-Karadzova and M. Vaeva, 1993: "Taxonomische Zusammensetzung der Diatomeen in Benthos des bulgarischen Schwarzmeerschelfes." Algologija, Kiev, in print.

Temniskova-Topalova, D., V. Petrova-Karadzova and E. Popova,: "Phytozonologische Charakteristik der Benthos-Diatomeenflora des bulgarischen Schwarzmeerschelfes." Algologija, Kiev, in print.

Valkanov, A., 1926: "Beitrag zur Kenntnis der Flagellaten Bulgariens." Bulletin de la Societe botanique de Bulgarie, I:105-120.

Valkanov, A., 1928: "Protistenstudien II. Notizen uber die flagellaten Bulgariens." Arch. Protistenk., 63(3): 419-450.

Valkanov, A., 1929: "Protistenstudien. 5-Hyphodictijein neuer Algenpilz." Arch. Protistenk., 67(1): 122-127.

Valkanov, A., 1932: "Notizen uber das Leben in den Hachgebirgssen Bulgariens." Travaux de la Societe bulgare des Sciences naturelles, 15-16:207-266.

Valkanov, A., 1933: "Uber die kinetische Energie einiger Zelbestandteile." Protoplasma, 20(I): 20-30.

Valkanov, A., 1934: Beitrag zur Hydrofauna Bulgariens. Sofia, p. 32.

Valkanov, A., 1934: "Eine rhizopodiale Euglena?." Arch. Protistenk., 83(2): 367-370.

Valkanov, A., 1935: "Notizen uber die Brackwasser Bulgariens. 1." Annuaire de l'Universite de Sofia, 3:249-303.

Valkanov, A., 1936: "Notizen uber die Brackwasser Bulgariens. 2. Versuch einer hydrographischen und biologischen Erforschung derselben." Annuaire de l'Universite de Sofia, 32(3): 209-341.

Valkanov, A., 1937: "Die Varnassen. Beitrag zur Hydrographie und Biologie derselben." Bulletin de la Societe geography de Bulgarie, 4:118-139.

Valkanov, A., 1938: "Hydrobiologische Untersuchungen an einigen Hohgebirgseen Bulgariens." Annuaire de l'Universite de Sofia, 34(3): 101-145.

Valkanov, A., 1941: "Beitrag zur Histologie von Hydra." Annuaire de l'Universite de Sofia, 37(3): 207-212.

Valkanov, A., 1941: "Uber die osmophile Substanz der Characeen." Protoplasma, 36(2): 247-253.

Valkanov, A., 1942: "Protistenstudien XI. 4. Ein neues parasitisches Chlamydomonas." Annuaire de l'Universite de Sofia, 3:31-60.

Valkanov, A., 1950: "Utersuchengen uber die Infection der Eier von Chlorhydra viridissima mit Zoochlorellen." Annuaire de l'Universite de Sofia, 46(3): 110-122.

Valkanov, A., 1954: "Beitrag zur Kenntnis unserer Schwarzmeerfauna." Trud. Morsk.-biol. st., 18:49-53.

Valkanov, A., 1955: "Notizen uber die Algae Pithophora ke kewenis Wittrock." Mitteilungen des Botanischen Instituts, 4:119-125.

Valkanov, A., 1957: "Katalog unsers Schwarzmeerfauna." Trud. Morsk. biol. st., 19:1-62.

Valkanov, A., 1962: "Uber die Entwicklung von Hymenomonas coccolithophora Conrad." Rev. Algol., 6(3): 220-226.

Valkanov, A., 1963: "Dir Chrysomonadae Prymnesium parvum als Ursache eines Massensterbens der Tiere in bulgarischen Strandseen." In: Progress in Protozoology, p. 341-343.

Valkanov, A., and T. Marinov, 1964: "Nachtrag zum Katalog der bulgarischen Schwarzmeerfauna." Bulletin de l'Institut de Zoology, 17:51-59.

Valkanov, A., 1964: "Korsikoviella vaucheriae n.g., n. sp. /Protococcineae/ und ihre Entwicklung." Arch. Microbiol., 48:247-258.

Valkanov, A., 1964: "Untersuchungen uber Prymnesium parvum Carter und seine toxishe Einwirkung auf die Wasserorganismen." Kieler Meeresforsch., 20(1): 65-81.

Valkanov, A., 1967: "Utersuchengen uber Chromophyton Rosanoffi Woronon, 1880." Bulletin de l'Institut de Zoology, 23:97-108.

Valkanov, A., 1968: "Notizen uber Volvulina steinii Playfair 1915, gefunden in Bulgarien." Bulletin de l'Institut de Zoology, 27:5-11.

Valkanov, A., 1968: "Sas Neuston." Limnologica, 6(2): 381-403.

Valkanov, A., 1968: "Zasammenhange und Vechselbeziehungen zwischen der Donau und dem Schwarzen Meer in hydrologischer und biologischer Beziehung." In: Limnologische Berichte der X. Jubilaumstagus der Arbeitsgemeinschaft Donauforschung, Bulgarien, 10-20 Oct. 1966, Sofia, p.

Vilhelm, J., 1907: "Ein Beitrag zur Kenntnis der Charophytenflora von Bulgarien, Montenegro und der Athos-Halbansel." Hedwigia, 42(1-2): 66-70.9-18.

Vilhelm, J., 1912: "Zweiter Beitrag zur Kenntnis des Charophytenflora von Montenegro und Bulgarien." Hedwigia, 531-2): 23-35.

Vilhelm, J., 1922: "Troisieme compte-rendu sur les Charophytes balcaniques." Acta Bot. Bohemica, I:65-66.

Vodenicharov, D., 1958: "Beitrag zur Algenflora Bulgariens." Mitteilungen des Botanischen Instituts, 6:431-438.

Vodenicharov, D., 1959: "Materialen zur Algenflora im Becken des Iskerflusses." Annuaire de l'Universite de Sofia, Faculte de biologie, geology, et geography, 51(1): 113-123.

Vodenicharov, D., 1959: "Beitrag zur Erforschung der Wasser und Algenflora und Vegetation auf dem Ljulingebirge." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 1(1): 61-82.

Vodenicharov, D., 1960: "Uber die Systematik und Verbreitung von drei sletemen Cyanophyceen." Annuaire de l'Universite de Sofia, Faculte de biologie, geology, et geography, 52(1): 105-129.

Vodenicharov, D., 1960: "Investigation of the genus Botrydium Wallr. in Bulgaria." Ukr. bot. j., 17(4): 61-66.

Vodenicharov, D., 1960: "New green algae." Ukr. bot. j., 17(2): 89-94.

Vodenicharov, D., 1960: "Beitrag zur Algenflora Bulgariens. II." Mitteilungen des Botanischen Instituts, 7:321-331.

Vodenicharov, D., 1960: "Beitrag zur Algenflora Bulgariens. III." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 52(1): 137-146.

Vodenicharov, D., 1960: "Beitrag zur Kenntnis der Susswasser Rotalgen in bulgarien." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 52(1): 153-161.

Vodenicharov, D., 1960: " Hydrobotanische Studies uber die Hochgebirgsseen in Bulgarien. I." Mitteilungen des Botanischen Instituts, 7:279-291.

Vodenicharov, D., 1961: "Gloeothece heufleri Grun. in Bulgaria." Bot. mater. otd. spor. rast., 14:111-114.

Vodenicharov, D., 1961: "Oedogonium parvulum sp. nov.." Feddes Report., 64(1): 82-85.

Vodenicharov, D., 1962: "Beitrag zur Algenflora Bulgariens. IV." Mitteilungen des Botanischen Instituts, 10:145-159.

Vodenicharov, D., 1962: "Hydrobotanische Untersuchungen uber das Urdino-Kar /N-W Rila-Gerbirge/." Annuaire de l'Universite de Sofia, Faculte de biologie, geology et geography, 54-55(1): 139-211.

Vodenicharov, D., 1963: "Beitrag zur Geographie der Algen. I. Verbeitung der Charophyceen in Bulgarien." Travaux Scientifiques de l'Ecole Normale Suoeieure, Plovidv, 1(1): 89-94.

Vodenicharov, D., 1963: "Beitrag zur Kenntnis der Gattung Micractinium Fries." Compt