Troglofauna

As Stygobionta (also: Stygobionte, Stygobite ) refers to creatures that live preferentially or exclusively in groundwater, which, therefore, on the biotope ( habitat ) of the Stygal specialized and have adapted to it.

Terminology

The habitat, groundwater is designated by the technical term Stygal his community as Stygon. The organisms that live there are called according to their degree of specialization ( specialized on this habitat, only exceptionally elsewhere occurring) as Stygobionte, Stygophile (preferably in groundwater, but occurring also in other aquatic habitats ) and Stygoxene ( specializing in different types of water, only exceptionally in groundwater). Be Separate from organisms that live specifically in caves waters, Troglobios called, they are classified according to Troglobionte, troglophile and Trogloxene ..

In pore systems under the river bed of surface waters, especially rivers will have its own zone, called Hyporheisches Interstitial separated. Their fauna is quite different from that of the ground water and more in conjunction with the surface water body.

Colonization spectrum

Important properties of the ground water as a habitat are: lack of nutrients ( oligotrophy ), oxygen shortage, to the anaerobic, high consistency and uniformity of the environmental conditions, for example, barely fluctuating temperatures in the annual cycle (no difference between summer and winter). In addition, the pore volume, and thus the inhabitable space, usually severely limited.

Most important group of organisms of groundwater are the prokaryotes. Their food base are mainly registered with the leachate organics, a not insignificant proportion are but lithotrophe and manage chemotrophe species in deeper layers, for example, methanogens and acetogenic that ( eg volcanic ) with geogenic produced carbon dioxide and hydrogen; they can reach depths of about 5 km in the crust. Due to the widespread lack of oxygen, anaerobic respiration pathways such as nitrate, sulfur respiration and iron respiration play (reduction of trivalent to divalent iron ions ) play an important role. The prokaryotes groundwater living far mostly not free floating, but are attached to surfaces. The species diversity of the ground water is considered high, but is poorly understood because can be less than one percent of the species grow on conventional culture media. The cell density is from 1000 to 100 million cells per cubic centimeter. Important colonizers are Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Nitrospira, Planctomycetes, Spirochaetes, Verrucomicrobia .. However, whether it specialized, are stygobionte bacterial species is still unclear.

Fungi play a relatively minor role in the groundwater. Typical representatives are Ascomycota, Zygomycota, Oomycetes, some Basidiomycota as Rhizomorpha subterranea. Also protozoa are more common, especially in contaminated groundwater, their density usually does not exceed 100 cells per gram of aquifer material. The protozoa of groundwater have hardly been explored. It outweigh flagellates are more common, according to previous studies Bodonida, Cercomonadida, Chrysomonaden, cryptomonads, Mastigamoebaea.

Groundwater animals

In Europe, more than 1220 species occur stygobionter stygophiler and animal species (including aquatic cave fauna). Stygobionta show remarkable morphological and physiological characteristics, compared with living organisms in the surface waters, which represent an adaptation to the special habitat. Is particularly striking here

Typical Stygobionte are small, often less than a millimeter body length and more or less vermiform ( Stemmschlängler ). Most can tolerate reduced oxygen content, but not anaerobic. Many show permanent ventilation movements to supply the water flow oxygen. Your change of place, for example, by swimming movements, however, is low. Despite the lack of eyes that most of a light sense, whereby they actively avoid light ( photophobic ).

The metabolism of Stygobionten operates at a low compared to related surface dwellers level mainly due to the food poverty of groundwater and the often low temperatures. Are typically slow growth, delayed development stages, but it longevity. Although the reproduction rate is less than the living of surface water organisms, the number of offspring per individual is almost identical due to the long life - span and thus reproduction. It is believed that the very unfavorable, but it completely uniform and predictable environmental conditions creates a selective pressure towards longevity at a low metabolic rate, this was called " A Strategy " (English adversity selection) circumscribed. Groundwater animals are very often phylogenetically old lines of development. Here, their propagation speed is low: Northern Europe ud North America are due to the types of losses caused by the ice ages to the present day settled quite poor in species. There are aquatic species, of which both stygobionte as surface waters colonizing populations are known, for example, Asellus aquaticus and Gammarus pulex.

Groups stygobionter Animals

Among the Stygobionten crustaceans are the most important representatives. More than half of the described species belonging to this sub-tribe. Numerically extend the Copepoda and Amphipoda out with many Stygobionten. The stygobiontischen Amphipoda the rich biodiversity is striking with more than a hundred Stygobionten in some genera such as Stygobromus and Niphargus .. Typical European Stygobionte are also the genera Bathynella ( Bathynellacea ) and Thermosbaena ( Thermosbaenacea ), outside Europe, there are many others such as the only in the southern hemisphere living Spelaeogriphacea. In these groups direct immigration is assumed from the sea.

Other taxonomic groups with Stygobionten are the planarians, snails, nematodes, water mites ( Hydra Carina ). True stygobionte vertebrates such as fish and amphibians do not exist, they can be found exclusively in cave waters or the like and usually with them the related karst waters.

Threat

Stygobionte species are today affected by anthropogenic interference in their habitat. Significant Beeinträchtigunggspfade are about groundwater use ( pumping) and groundwater pollution. Play an important role in oxygen depletion due to increased biomass Einschwemmung and constipation ( clogging ) of the gap system is flooded by fine-grained material. The effects are not well known in detail, and in the exploitation of often ignored .. Because of their lifestyle Stygobionte are particularly sensitive to habitat changes of all kinds and are after disturbances barely able to make the earlier settlement again.

Swell

• Wilfried Schönborn, Ute Risse- Buhl: Textbook of limnology. Swiss Barth Verlag, Stuttgart 2nd edition, 2013. ISBN 978-3-510-65275-4