[NB04]
Subterranean biodiversity
Assessments published: [ 2007 ]

The indicator shows the number of species in subterranean habitats in Slovenia. Only obligate subterranean species, also known as troglobitic species, have been taken into consideration. The figures have been rounded off, since they are constantly on the rise due to the advancements in research. The number of species in subterranean waters, i.e. cave as well as sandy and gravelly alluvia, encompasses approximately 8% of all freshwater fauna in Europe. The share of terrestrial cave fauna cannot be determined.

A considerable predominance of obligate subterranean species over surface immigrants in the subterranean water body also suggests a high level of cleanliness and thereby the usefulness of subterranean water.

Image NB4-1: Slovenian subterranean biodiversity compared to the subterranean biodiversity of nearby countries and North America by number of obligate subterranean species – troglobites

Source: Database Subterranean fauna of the wider Dinaric area, Department of Biology, Biotechnical University, University of Ljubljana, 2007.


Image NB4-2: Number of troglobitic points in Slovenia (*Note: There is no terrestrial subterranean fauna in the interstitial water of the Ljubljana Plain [Ljubljansko polje])

Source: Sket, Zagmajster, 2004.


Image NB4-3: Selected points with the richest subterranean fauna in Slovenia, evaluated according to the provisional scoring system by the Department of Biology at the Biotechnical Faculty at the University of Ljubljana

Source: Sket, Zagmajster, 2004.


Image NB4-4: Density of exclusively cave-dwelling beetles in Slovenia and in its surroundings. (Calculated for the number of species per 400 km2 squares.)

Source: map prepared by: M. Zagmajster; basis: Database Subterranean fauna of the wider Dinaric area, Department of Biology, Biotechnical University, University of Ljubljana.


To preserve a high level of biodiversity and to halt the decline in biodiversity by 2010:
– to preserve or to achieve a favourable state of species and habitat types which are endangered or located in areas designated as important for the preservation of biodiversity (for example the Ramsar localities).

Slovenia has an exceptional number of obligate subterranean species. It seems that aquatic fauna with 200 species is by far the richest, while the terrestrial fauna with 150 species is second only to more southern parts of the Dinaric Karst. Roughly 55% of aquatic fauna is comprised of tiny crabs, while 25% are little snails. Over 50% of terrestrial species are beetles. The highest density of species is in the Dinaric Karst in southern Slovenia and other Karst areas, some aquatic fauna is also found in groundwater in non-Karst lowlands.

The number of obligate subterranean species by individual cave systems is also high. As many as five Slovenian cave systems have been listed among the 20 richest cave systems in the world. The Postojna-Planina Cave System with its 50 water and 35 terrestrial species is by far the most abundant. Another advantage of this system is the plethora of "young" surface immigrants in the underground stream and the entrance passages. Of special interest are species which are progressively better adjusted to the subterranean world as we move along the underground stream. Apart from caves, a very high number of species are also found in the water of the gravelly lowlands of the Ljubljana Plain (Ljubljansko polje).

Most subterranean animals are not threatened by collectors (scientists or merchants), they are, however, all threatened by pollution, which normally originates from the surface. Many substances also pose a direct threat to the underground life. The introduction of seemingly less dangerous organic substances into the underground enables the invasion of surface species, which are driving out obligate subterranean species. Water in the underground purifies itself only to the level of nitrates, which then accumulate. Therefore merely the proteus and subterranean beetles require and are given special protection by the Decree on protected wild animal species (OG of the RS, Nos. 46/2004, 109/2004, 84/2005, 115/2007 and 32/08-decCC). This decree also protects the habitats of other subterranean species, i.e. the subterranean environment as a whole. Apart from that, a substantial part of especially biodiverse areas is partly under Natura 2000 protection, while only the rather poor subterranean fauna of the Škocjan Caves is under special protection (as a Ramsar wetland).

The state of waters in sandy and gravelly deposits below the plain surfaces is deteriorating; there are also fewer and fewer usable wells where it is rather simple to monitor the conditions. The state has deteriorated significantly in certain places in the Karst areas as well. The invasion of surface species along the underground stream was observed in the Postojna-Planina Cave System in the post-war period, but after remediation the state has improved. The state around Kočevje is extremely bad. Some subterranean waters are polluted due to intensive stockbreeding, others due to landfills; the once exceptionally dense proteus colonies have since disappeared. Similar phenomena can be observed elsewhere, though to a smaller extent; animals previously present in not particularly polluted caves often cannot be found anymore. There is no systematic monitoring of these changes.

The majority of obligate subterranean species are endemic. This means that they are only limited to a certain place or area. They are mostly limited to the southern half of Slovenia, many of them even to a much narrower area. In addition, their general habitats are broken up into various small patches, making all these species endangered.

The Department of Biology at the Biotechnical Faculty of the University of Ljubljana collects detailed data on the abundance of species in subterranean habitats for all areas of the former Yugoslavia in the database Subterranean fauna of the wider Dinaric area. The register includes published and yet unpublished data. Data beyond this area are collected and published only for a smaller number of countries, while data for areas with the same surface (which are thus comparable) are still being prepared. The numbers for Bulgaria and the US have been derived from the publications by their local researchers.

With a view to nature protection, the Department of Biology at the Biotechnical Faculty at the University of Ljubljana has created a scoring system for the evaluation of objects. The numbers of obligate subterranean species – troglobites, as well as their endemism, typical localities, etc., are taken into consideration. Points are added for non-troglobitic fauna and other ecological aspects, such as bat colonies, the underground stream fauna, habitat diversity, etc. Points are also added for non-biological aspects: cultural-historical significance, aesthetic values, education, economy (tourism, drinking water) and other aspects.

- Sket, B., 1972. Zaščita podzemeljske favne se ujema z življenskimi interesi prebivalstva [Subterranean fauna protection matches the main interests if the population]. In: Zelena knjiga [Green book], Natural History Association of Slovenia, Ljubljana 137-140, 164-165
- Sket B., 1979. Jamska favna Notranjskega trikotnika (Cerknica - Postojna - Planina), njena ogroženost in naravovarstveni pomen [Cave fauna of the Notranjska triangle (Cerknica – Postojna – Planina), its endangerment and significance for nature conservation]. Varstvo narave [Nature Conservation], Ljubljana, 12: 45-59
- Sket B., 1992. Rdeči seznam ogroženih živali podzemeljskih voda v Sloveniji [Red list of endangered subterranean water fauna in Slovenia]. Varstvo narave [Nature Conservation] 17: 193-204
- Bole J., Drovenik B., Mršić N., & Sket B., 1993. Endemic animals in hypogean habitats in Slovenia. Naše Jame - Our Caves, 35(1): 43-55
- Sket B., 1996. Biotic diversity of hypogean habitats in Slovenia and its cultural importance. Biodiversity - Intern. Biodiversity Seminar, UNESCO, Gozd Martuljek, Proceedings: 59-74
- Sket B., 1997. Biotic diversity of the Dinaric karst, particularly in Slovenia: history of its richness, destruction, and protection. Conserv. Prot. Biota of Karst, Karst Water Inst., Spec. Publ. 3: 84-98
- Culver D.C. & Sket B., 2000. Hotspots of subterranean biodiversity in caves and wells. Journal of Cave and Karst Studies 62(1): 11-17
- Sket B., 2004. Postojna-Planina Cave System: biospeleology. In: Gunn J. ed., Encyclopedia of Cave and Karst Science, Fitzroy Dearborn, New York London, pp. 603-604.
- Sket, B., K. Paragamian, and P. Trontelj, 2004. A census of the obligate subterranean fauna in the Balkan Peninsula. In: H.I. Griffiths & B. Krystufek (eds), Balkan Biodiversity. Pattern and Process in Europe's Biodiversity Hotspot. Kluwer Academic Publishers B.V., pp 309-322.
- Sket, B., Zagmajster, M., 2004. How to inventory and evaluate the biologically important subterranean world heritage? The case of Slovenia.(abstract). Acta carsologica 33(2, suppl. 1): 28.
- Sket B. (2005) Subterranean animals in Slovenia: protecting habitats, not specimens. New currents in conserving freshwater systems (Ed J. Stenzel), p. 22. American Museum of Natural History-Center for Biodiversity and Conservation, New York.

June 2007

Apology: The translations haven't been approved by authors yet.

Boris Sket, Department of Biology - Biotehnical Faculty