03H1
Volcanic caves
Relationships with habitat classifications. EUNIS: H1.24 Troglophilic invertebrate caves, H1.25 Subtroglophilic invertebrate caves; PAL. CLASS.: 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 B1 C2 D3 E1 F1 H3 L1].
General characteristics. The volcanic caves in Bulgaria occur only in areas with past paleovolcanic activities. The most significant area (more than 3600 km2) covered by volcanogenic rock formations is in Rhodopi Mts. There was a strong volcanic activity in Palaeogene in East Rhodopi Mts. which took place partly on the bottom of a shallow and warm sea and partly on the land. The primary volcanic caves discovered in Bulgaria belong to three main types: lava shafts, lava caverns and under-lava holes. The secondary volcanic caves have occurred in lava rocks and lava tuffs after they had been destroyed. They are lateral-erosion caves (most of the volcanic caves are along Arda, Varbitsa and Krumovitsa rivers), gravitation-erosion caves (that occurred in volcanic rocks broken into large pieces; the cracks are broadened by erosion processes), rock bridges and arcs (mainly in the pyroclastic rocks in the valleys of large rivers like Mosta locality near Draganovo village and Hobota locality near Sredna Arda village) and anthropogenic caves (mainly ancient mines like Ini-Kler locality near Stemtsi village). The caves that are in contact zones are particularly interesting, e.g. volcanic-karst caves that are a result from the deposition of palaeogenic coral reefs on thin layers and lenses among the volcanic depositions. In such coral reefs are Maarata cave near Madretsi village, Tilki-Ini near Ostrovitsa village, Trite Pesteri cave near Letovnik village and several other caves near Karzdhali town. Approximately 90 caves of volcanic origin are known from Bulgaria; their entrances are usually large and the galleries, between 5 and 20 m long, in most cases do not branch. Conditions typical for caves– complete darkness and high humidity - occur only in rare cases. The biggest volcanic cave in Bulgaria, Golyamata Pestera cave (Kodzha-In) near Byal Kladenets village, Haskovo area is a cavity that was formed below the lava with an entrance of 14 m wide and 5 m high. The cave has one floor, two large semi-light halls whose total area is 120 m2; the volume is approx. 640 m3 and the length 51 m. Due to the short length of Bulgarian volcanic caves, the microclimate, humidity and air currents are strongly dependent on the outside environment. Cave invertebrates, troglophils and trogloxenes, have been discovered in almost all caves that have been studied. Only one beetle that is more adapted to underground life in volcanic rocks has been discovered in East Rhodopi Mts., Troglorrhynchus beroni. A few butterfly species often occur. From April until the end of September some caves in East Rhodopi Mts. are inhabited by large reproducing colonies of the bat species Miniopterus schreibersii (3000–5000 indiv.), Myotis blythii and M. myotis (up to 4000 indiv.), M. capaccinii (up to 3000 indiv.) and M. emarginatus (up to 7000 indiv.). Sometimes nests of Hirundo daurica and Phoenicurus spp. can be found near the entrances.
Characteristic taxa.
- Animals: Gastropoda – Balcanodiscus frivaldskyanus; Araneae – Meta spp., Pholcus spp., Tegenaria spp., Coleoptera – Laemostenus cimmerius, Troglorrhynchus beroni;Lepidoptera – Autophila dilucida, A. limbata, Hypena rostralis, Inachis io, Pyrois effusa, Triphosa spp.; Chiroptera – Miniopterus schreibersii, Myotis blythii, M. capaccinii, M. emarginatus, M. myotis, Rhinolophus spp.
Distribution in Bulgaria. The largest number of volcanic caves has been discovered in the central parts of East Rhodopi Mts. In the lower parts of Northeast Rhodopi Mts. 25 caves have been mapped; in the lower parts of Southeast Rhodopi Mts., 42 caves are known, and in the Madzharovo depression more than 10 caves are situated around the crater area of the Madzharovo palaeovolcano. Volcanic caves have been discovered in several places of West Rhodopi Mts. and the southern parts of Struma River valley, particularly in the crater of the early-Miocene volcano Kozhuh Mts. The altitude is 120–450 m.
Conservation importance. Some of the volcanic caves in East Rhodopi Mts. are important dwellings for bats in Bulgaria. Up to 12000 individuals of three to five bat species live there in summers.
Threats. The entrances of many volcanic caves are enclosed with walls to retain domestic animals. The floor of such caves is covered by manure, while the walls are covered by symbovilic and coprophilic flies (Calliphora spp., Musca spp., Sepsis spp., etc.) as well as parasites that are not typical for the cave environment. The constant use of the caves by men makes them practically unsuitable for reproduction of the colonial bat species. The presence of people from May until end of July coincides with the reproductive period of the bats.
Conservation measures taken. The habitat is included in Annex № 1 of BDA. Approximately 12 volcanic caves are within the borders of Sredna Arda Protected Area, 3 caves are in Gyurgena Protected Area, and 4 are in Golemia Sipei Protected Area. A significant part of the volcanic caves are within sites of the European Ecological Network NATURA 2000.
Conservation measures needed. Elaboration of management plans for the existing protected areas with volcanic caves and regulation of restriction for stockbreeders.
References. Gospodinov 2001; Kolev 1989; Benda et al. 2003; Beron et al. 2004, 2006.
Author: Boyan Petrov
