02H1
Continental caves
Relationships with habitat classifications. EUNIS: H1.221 Continental subtroglophilic vertebrate caves, H1.231 Troglobiont invertebrate temperate caves, H1.24 Troglophilic invertebrate caves, H1.25 Subtroglophilic invertebrate caves; PAL. CLASS.: 65.25 Continental bat caves, 65.41 Troglobiont invertebrate temperate caves, 65.5 Troglophilic invertebrate caves, 65.6 Subtroglophilic invertebrate caves; HD 92/43: 8310 Caves not open to the public.
Conservation status. BDA, BC, HD.
Category. Vulnerable [VU – A1, 2 C1 D2 E2 F1 G1 H2 I J L1].
General characteristics. The continental caves are natural hollows in the rocks that are accessible to people. Most often they occur in karst areas where the speed of karstification depends on the degree of fissuration of the rocks, temperature conditions, rainfalls, etc. Karstification is based on the dissolving of the bedrock in the water, the formation of HCO3 and consequent increase of the content of CO2. The mechanical influence of the running water also contributes to the formation of cave galleries. Parallel to primary cave formation, secondary processes of deposition of carbonate substances also take place as a result of which a rich calcite decoration of the caves appear: stalactites, stalagmites, stalactones, rimestone pools, calcite accumulations, helictite and aragonite crystals and many others. The length of the cave galleries varies from 5 m to over 15 km. The caves can form a single tunnel or be a complex system of connected galleries even with several layers. According to their hydrological regime they are dry caves, but often with water dripping from the ceiling or water caves through with running rivers or cave lakes. The microclimatic conditions in the caves are relatively constant and the air temperature is close to the average annual temperature in the respective area. An important feature of the cave habitats is the absence of sunlight and respective absence of photosynthesizing organisms. These are systems that fully depend on the surface environment and the water that penetrates is the main source of organic materials (dissolved organic substances, detritus, dead organisms, etc.). The organisms that enter underground and those which use the caves as their shelter during part of their life cycle can also be source of nutrition substances, mainly with their excrements. The animals that live in the caves have adapted to their environment to a different extent. The clay floors, wet sintric walls and shapes, the wet gravel deposits, etc. create favourable conditions for the land cave fauna, while the water animals live in the rimestone pools and ponds, underground rivers and streams, wet sands rich in gravel, etc. The typical inhabitants – invertebrate troglobionts (both water and land species) – are completely or partly unpigmented and very often with strongly reduced or absent visual receptors. Their life cycle takes place mainly in underground conditions. A considerable number of the troglobionts are relic species. The aboveground ancestors of these living fossils belonged to already extinct aboveground faunal complexes. There are more than 800 species belonging to four groups of hypogean animals – trogloxenes, troglophils, troglobionts and stigobionts. Most important from conservation and zoogeographic points of view are approx. 160 species of troglobionts and stigobionts, many of which occur only in one single cave or in few caves within the borders of a certain area. 780 caves in Bulgaria have been studies biospeleologically. The most species-rich caves are located in Vrachanska Mts., West and Central Balkan Range, West Rhodopi Mts. Some of the most ancient groups of invertebrate animals in the Bulgarian caves are the underground isopods from the genera Sphaeromides and Protelsonia, whose marine ancestors have inhabited the waters of the ancient Tethys Ocean 60 million years ago. The limited possibilities for migration of the populations of the cave invertebrates from one karst area to another and often even their complete isolation are the driving force of geographic speciation at different speeds in the different animal groups, hence the well-expressed endemic characteristics of the cave fauna in Bulgaria. The caves and abysses are an important roost for approx. 10 species of cave bats which reproduce and spend winter in colonies inside. A considerable quantity of guano accumulates on the cave floor in the places where the bat colonies live. This large quantity of organic material presupposes the development of rich and numerous coenoses of invertebrate guanobionts, mainly oligochaetes, collembolas and diptera that are the food of the carnivorous hylobionts, carabid beetles, staphylinides, etc.
Characteristic taxa.
- Animals: Copepoda – Acanthocyclops chappuisi, A. iskrecensis, A. radevi, A. strimonis, Bryocamptus typhlops, Elaphoidella balkanica, E. cavernicola, E. pandurskyi, Parastenocaris bulgarica, Speocyclops infernus, S. lindbergi, S. rhodopensis, Stygoelaphoidella bulgarica, S. elegans, S. stygia; Isopoda – Bureschia bulgarica, Protelsonia bureschi, P. lakatnicensis, Sphaeromides bureschi, Trichoniscus bulgaricus, T. rhodopiense, T. tranteevi; Amphipoda – Niphargus spp.; Opiliones – Paralola buresi, Siro beschkovi, Tranteeva paradoxa; Pseudoscorpiones – Balkanoroncus spp., Chtonius spp., Neobisium spp., Roncus spp.; Araneae – Centromerus bulgarianus, Protoleptoneta bulgarica, Troglohyphantes drenskii; Myriapoda – Apfelbeckiella spp., Balkanopetalum spp., Bulgarosoma bureschi, Eupolybothrus andreevi, Stygiosoma beroni; Coleoptera – Duvalius (Paraduvalius) spp., Pheggomisetes sp. Rambousekiella ledenikensis; Mammalia – Chiroptera: Rhinolophus ferrumequinum, Miniopterus schreibersii, Myotis blythii, M. capaccinii, M. emarginatus, M. myotis, Rhinolophus euryale, Rh. hipposideros, Rh. mehelyi.
Distribution in Bulgaria. The karst areas in Bulgaria cover about 22,7% of its territory. According to the geographic zonation there are four physical-geographic zones in Bulgaria – Danubian plain (divided in 8 cave areas), Sredna Gora – Thracian Lowland area (10 cave areas), Balkan Range (19 cave areas) and Rila-Rhodopi Mts. area (13 cave areas). Until September 2007, 5470 caves and abysses have been discovered and studied (www.hinko.org). Only nine of them are open to the public. The number of underground objects is dynamic and constantly increases as a result of the discovery of new caves in understudied areas.
The longest caves in Bulgaria are :
- Duhlata cave Bosnek village – Pernik municipality, more than 17,600 m
- Orlova Chuka cave – Pepelina village – Dve Mogili municipality, 13,437 m
- Yagodina cave – Yagodina village – Borino municipality, 8501 m
- Temnata Dupka cave – Lakatnik railway station – Svoge Municipality, more than 7000 m
The deepest abysses in Bulgaria are*:
- Raychova Dupka abyss – Cherni Osam village – Troyan municipality, 387 m
- Barkite № 14 abyss – Gorno Ozirovo village – Varshets municipality, 356 m
- Golyamata Yama cave – Kipilovo village – Kotel municipality, 350 m
- Tizoin abyss – Gubesh village – Godech municipality, 320 m
The caves and abysses occur from 30 m alt. (caves in the lower part of the karst valley of Batova River) up to 2650 m alt. (Vichren abyss) in Pirin Mts.
Conservation importance. A considerable part of the Bulgarian caves have unique and rich calcite decoration. The terrestrial and water fauna consists exclusively of relic and endemic species. The caves are of utmost importance as shelters of large bat colonies.
Threats. Unregulated economic activities inside and outside the caves. Some caves have been used for mushroom cultivation, as dairies and as storage areas. These activities in most cases are not in conformity with the principles for conservation of the cave fauna and cave speleothems. Unregulated overexploitation as tourist sites. Activities of “treasure hunters”. Opening or expanding of stone pits. Purposeful or involuntary destructions – deposition of solid and liquid waste, breaking of the cave formations, fires. Visits to the caves during the reproductive period of the bats and related direct killings and constant disturbance.
Conservation measures taken. Approx. 120 caves together with limited surrounding areas have been declared as Protected Sites. Many of them are within protected areas (Pirin and Central Balkan National Parks) and Vrachanski Balkan, Vitosha, Strandzha, Shumensko Plato and Rusenski Lom Nature Parks). Approx. 42 caves are included as separate protected sites in the European Ecological Network NATURA 2000. Large cave areas or large parts of these areas are within this network.
Conservation measures needed. Proclamation of the caves with rich biodiversity and unique cave speleothems as protected areas. Elaboration of regulations for the opening of new caves to the public. Approval of management plans for protected karst areas with caves. On-site control of the visitors in caves protected as important bat shelters. Education programs for the population of the karst areas and final adoption of the Cave Act.
References. Benda et al. 2003; Beron 1972, 1994, 2007; Beron & Gueorguiev 1967; Guéorguiev 1977; Pandourski 2007; Popov 1976; Vandel 1964.
Authors: Ivan Pandourski, Boyan Petrov
