Collins New Naturalist Library

Various free-living algae, such as Chlorella, Scenedesmus and Pleurococcus are found growing deep inside caves. Though able to synthesize pigments in the dark, they appear to use non-photosynthetic metabolic pathways. The other plant phyla Rhodophyta, Phaeophyta, Bryophyta are essentially absent from the dark parts of caves. The phylum Tracheophyta is represented by a very few aberrant saprophytic species which can live independently of sunlight.

Kingdom FUNGI

Phyla Zygomycetes, Ascomycetes, Basidiomycetes, Myxomycetes

Fungi are important in cave ecosystems. Most are saprophytic on organic material washed into caves and form the main food base of cave communities. Some are epizoic (live on the outer surface of animals) or parasitic. Most members of the phylum Oomycetes are parasitic on flowering plants and therefore not represented in caves.

Kingdom ANIMALIA

Phylum Porifera

Encrusting sponges may be the commonest organisms in tidally flushed submarine caves.

Phylum Coelenterata

Hydra viridissima occurs in groundwaters in the Southern Carpathians of Europe. Marine Hydrozoa and Anthozoa are commonly found in submarine caves.

Phylum Platyhelminthes

Rhabdocoel Turbellaria are common in wells, springs and groundwaters. Cave-evolved Triclads have a worldwide distribution, with most species within three planarian families: Dendrocoelidae, Kenkiidae and Planariidae.

Phylum Nematoda

Free-living nematodes are frequent in groundwaters, caves and mines worldwide. Several freshwater species of the otherwise exclusively marine Desmoscolecidae inhabit caves in Slovenia.

Phyla Nemertinea and Rotifera

A few species of these small creatures inhabit interstitial waters and caves.

Phylum Annelida

Submarine caves often contain huge populations of sedentary polychaete worms and a number of cave-evolved freshwater polychaetes are known from Switzerland, Slovenia, Japan and Papua New Guinea. Oligochaete worms are often abundant in caves, in groundwaters and sediments. The family Lumbriculidae contains many essentially cavernicolous species. Cavernicolous leeches are known from Central Europe and several tropical countries.

Phylum Mollusca

There are many cavernicolous Gastropoda within the families Auriculidae, Zonitidae, Subulinidae, Enidae and Valloniidae (terrestrial species), and Hydrobiidae (aquatic species). The Bivalvia include cavernicolous species of Pisidium and Congeria in Europe and Japan.

Phylum Onychophora

The South African species Peripatopsis alba is known only from caves.

Phylum Arthropoda

Subphylum Crustacea

Class Remipedia: Recently discovered in submarine caves in the Bahamas and Canary Islands, these actively swimming predators resemble aquatic centipedes.

Class Ostracoda: There are many groundwater species, some of which also occur in larger caves.

Class Copepoda: Many cyclopoids and harpacticoids occur in caves and interstitial groundwaters worldwide.

Class Malacostraca: The monospecific order Spelaeogriphacea is so far known only from caves in South Africa. Thermosbaenacea and Mysidacea are widespread in submarine caves and brackish groundwaters and a few species have made the evolutionary shift into freshwater caves. Isopoda are one of the best-represented orders in the subterranean world, with hundreds of cavernicoles described within the Asellidae and Oniscoidea. The Amphipoda, notably the Gammaridae, are equally well represented. Cavernicolous decapods such as crayfishes, galatheids, crabs and river prawns are particularly widespread in the tropics. Groundwater-inhabiting members of this class often belong to ancient lineages and the distributions of related taxa provide important evidence in reconstructing the history of the planet.

Subphylum Uniramia

Class Diplopoda and Pauropoda: Worldwide there are hundreds of species of cavernicolous millipedes, and particularly of Polydesmoidea. They often show relictual distributions which mirror past configurations of the earth’s crustal plates, long since redistributed by seafloor spreading and continental drift. A few Pauropoda are known from caves.

Classes Chilopoda and Symphyla: Cavernicolous Scolopendromorphs and Lithobiomorphs are known from European caves. In the tropics there are also cave-evolved Scutigerids. The Symphyla live in the soil and look like cave animals, but most feed on living plant roots and so are excluded from deep cave habitats.

Class Insecta: The Collembola and Diplura are primitive, wingless, ground-dwelling insects which require a high humidity. They include a large number of cave-evolved species worldwide. Cavernicolous Blattodea are mostly confined to the tropics. Within the Orthoptera, the Rhaphidophoridae or camel crickets contain a number of conspicuous cavernicoles with a worldwide distribution and a few cavernicolous gryllids are found in the tropics. There are cave-evolved Dermaptera, Psocoptera, Hemiptera, Trichoptera, Lepidoptera and Diptera. Not surprisingly, the majority of cavernicolous insects belong to the largest order and the most successful group of animals on earth, the beetles (Coleoptera). At least 22 families contain cavernicoles, which reach their greatest diversity and specialization in the Trechidae and Leiodidae.

Subphylum Chelicerata

Class Arachnida: A few cavernicolous Scorpiones, Uropygi, Amblypygi, Schizomida, Ricinulei and Palpigradi are known from tropical regions. Pseudoscorpions are well represented in caves, with over 300 cavernicolous species, many of which are giants among their kind, with very long legs and claws. The Opiliones also contain cavernicoles, most notably in the families Phalangodidae, Travuniidae and Ischyropsalidae. The terrestrial mites (Acari) most frequently found in caves are tiny Gamasides within the families Parasitidae, Rhagidiidae and Eupodidae and there are many cavernicolous water mites in the families Hydrachnellae and Porohalacaridae. Spiders (Araneae) dominate the predator niches in most tropical caves and include hundreds of cavernicolous species worldwide. In temperate regions, the most specialized cavernicoles belong to the primitive families Dysderidae, Leptonetidae, Telemidae and Oonopidae, but there are also many specialized species of Linyphiidae, Erigonidae and Agelenidae.

Fig. 2.3 Neobisium spelaeum, a giant cavernicolous pseudoscorpion which preys on the cave beetle Leptodirus hohenwarti (shown in Fig. 2.2)

Phyla Tardigrada and Bryozoa

A few species inhabit groundwaters.

Phylum Echinodermata

Various detritivorous brittle stars (Ophiuroidea) and sea cucumbers (Holothuroidea) frequently occur in submarine caves, but no strictly cavernicolous species are known.

Phylum Chordata

Class Teleostomi: Freshwater cavernicolous fishes are found mainly in the more arid regions of the world. To date around 60 more or less blind and depigmented species representing 8 orders and 13 families have been collected in freshwater and submarine caves, springs and groundwaters. The most speciose families are Cyprinidae, Gobiidae and Bythitidae, followed by Pimelodidae, Characidae, Cobitidae and Amblyopsidae.

Class Amphibia: 14 species of cavernicolous Urodela are known from North American caves and one from Europe. The latter, Proteus anguinus was the first cavernicole to be recognized as such. In common with species of the American genera Gyrinophilus, Eurycea, Typhlomolge and Haideotriton, Proteus retains larval gills in the adult stage, and is thus able to live permanently beneath the water table.

Class Reptilia: The colubrid snake Elaphe taeniura is a common inhabitant of caves in south-east Asia, from China to Borneo, where it preys on bats and swiftlets.

Class Aves: While no birds live permanently in caves, swiftlets of the genus Aerodramus (Apodidae) and the oilbird Steatornis caripensis (Caprimulgidae) are dependent on caves as nesting sites and are capable of navigating long distances underground and in total darkness by echolocation using ultrasonic clicks.

Class Mammalia: It is possible that a South American mouse Heteromys anomalus and one or two species of tropical shrews in the genus Crocidura may establish permanent cave populations. Many bats (e.g. Tadarida spp.) are dependent on caves for shelter, but none are cavernicolous.

In summary, although green plants are largely absent from caves, cavernicolous species are found within most of the major classes of animals, and are particularly common among the Crustacea, insects, spiders and millipedes.

Caves in limestone (#ulink_12d3b19e-65a7-5744-8741-1142c274359a)

Of several cavernous rocks in Britain and Ireland, one above all others provides extensive integrated cave systems of a size which allows the biologist to study the life they contain with relative ease. It is the Carboniferous Limestone.

Fig. 2.4 The blind North American cave fish Speleoplatyrhinus poulsoni has an extraordinarily developed lateral line system, with correspondingly enlarged brain parts for processing tactile and positional information.

The cave-bearing limestones are concentrated in six major patches: in County Fermanagh (the largest, but least well prospected area), the Northern Pennines, Derbyshire’s Peak District, County Clare, Somerset’s Mendip Hills and South Wales. In the Northern Pennines alone, there are 1800 or more documented cave entrances and around 350 km of explored and mapped cave passages – while current estimates give the total length of mapped passages in Britain and Ireland at somewhere around 800 km. Cave exploration is still in a very active phase in these islands, and significant new discoveries are still being made. For example, recent explorations in Ogof Daren Cilau beneath Mynydd Llangattwg in South Wales have yielded over 20 km of new discoveries in less than two years, including the largest passages yet found in Britain.

By any standards, 800 kilometers of open cave passage represents a significant habitat, worthy of the attention of naturalists – yet passages of explorable size must form but a tiny proportion of the total cave habitat, the vast majority being of mesocavernous dimensions. In the absence of data, I would guess that the habitable surface area within the mesocaverns of limestone terrains must run to at least two or three orders of magnitude more than that within explored caves.