Stygobionta

from Wikipedia, the free encyclopedia

As troglofauna : (also referred Stygobionte, Stygobite) to creatures that preferentially or exclusively in groundwater live, so to the biotope (habitat) of Stygal have specialized and adapted.

terminology

The groundwater habitat is referred to with the technical term Stygal, its community as Stygon. The organisms living there are referred to as stygobionts (specialized in this habitat, only occurring in exceptional cases elsewhere), stygophiles (preferably found in groundwater, but also in other aquatic habitats) and stygoxenes (specialized in other types of water, only in exceptional cases) according to their degree of specialization Groundwater). Organisms that live specifically in cave waters are called troglobios (see article: cave animals ), and they are divided into troglobionts, troglophiles and trogloxes.

A separate zone, called the hyporheic interstitial , is separated in the system of gaps under the bed of surface water, especially flowing water . Their fauna is completely different from that of the groundwater and is more related to surface water.

Settlement spectrum

Important properties of the groundwater as a habitat are: nutrient poverty (oligotrophy), oxygen shortage, up to anaerobia , high constancy and uniformity of the environmental conditions, for example hardly any fluctuating temperatures even in the course of the year (no difference between summer and winter). In addition, the pore volume, and thus the space that can be colonized, is usually very limited.

The most important group of organisms in the groundwater are the prokaryotes . Their food base is mainly organic substances introduced with the seepage water, but a not insignificant proportion are lithotrophic and chemotrophic species, in deeper layers, for example, methanogens and acetogens that get by with geogenic (e.g. volcanic) produced carbon dioxide and hydrogen; these can reach depths of over 5 kilometers in the earth's crust. Due to the widespread lack of oxygen, anaerobic pathways such as nitrate breathing , sulfur breathing and iron breathing (reduction of trivalent to divalent iron ions) play an important role. Most of the prokaryotes in the groundwater do not swim freely but are attached to surfaces. The species diversity of the groundwater is considered to be high, but has hardly been researched because less than one percent of the species can be reproduced on conventional nutrient media. The cell density is between 1,000 and 100 million cells per cubic centimeter. Important colonists are Proteobacteria , Acidobacteria , Bacteroidetes , Chloroflexi , Firmicutes , Nitrospira , Planctomycetes , Spirochaetes , Verrucomicrobia . However, it is still unclear whether there are specialized, stygobiont bacterial species.

Fungi play a comparatively minor role in groundwater. Typical representatives are Ascomycota , Zygomycota , Oomycota , some Basidiomycota such as Rhizomorpha subterranea . Even protozoa are more common, especially in contaminated groundwater, its density does not usually exceed 100 cells per gram of aquifer material. The protozoa of the groundwater have so far hardly been researched. Flagellates predominate ; according to previous investigations, bodonida , cercomonadida , chrysomonads , cryptomonads , mastigamoebaea are more common .

Groundwater animals

see also groundwater animals

In Europe there are more than 1220 species of stygobionter and stygophilic animals (including the aquatic cave fauna). Stygobionta show remarkable morphological and physiological peculiarities compared to living things in surface water , which represent an adaptation to the special biotope. It is particularly noticeable

  1. the lack of pigmentation
  2. the lack of eyes and the reduction of longer body attachments.

Typical stygobionts are small, often less than a millimeter in length and more or less worm-shaped (stalk snakes). Most can tolerate decreased oxygen levels, but not anaerobia. Many show constant ventilation movements in order to add oxygen with the water current. Your change of location, e.g. B. by swimming movements, however, is low. Despite the lack of eyes, most of them have a sense of light, whereby they actively avoid light ( photophobic ).

The metabolism of the stygobionts works mainly due to the lack of food in the groundwater and the often low temperatures at a low level compared to related surface inhabitants. Slow growth and delayed stages of development, but longevity at the same time, are typical. Although the reproduction rate is lower than that of organisms living in surface water, the number of offspring per individual is almost identical due to the long life span and thus also the reproductive span. It is assumed that the rather unfavorable, but completely uniform and predictable environmental conditions create a selection pressure in the direction of longevity with a low metabolic rate; this was described as the "A strategy" (adverse selection). Groundwater animals are very often phylogenetically old lines of development. Their speed of propagation is slow: Northern Europe and North America are relatively poorly populated due to the loss of species during the ice ages. There are aquatic species of which both stygobionte and surface water populations are known, for example Asellus aquaticus and Gammarus pulex .

Groups of stygobiont animals

Crustaceans are the most important representatives of the stygobionts . More than half of the species described belong to this sub-stem . In terms of numbers, the Copepoda and Amphipoda stand out with many stygobionts. In the case of the stygobiont Amphipoda, the great diversity of species is striking , with more than a hundred stygobionts in some genera such as Stygobromus and Niphargus . Typical European stygobionts are also the genera Bathynella ( Bathynellacea ) and Thermosbaena ( Thermosbaenacea ), outside of Europe there are numerous others, such as the Spelaeogriphacea , which only lives in the southern hemisphere . Direct immigration from the sea is assumed for these groups.

Other taxonomic groups with stygobionts are the planarians , snails , nematodes , and water mites ( Hydracarina ). There are no real stygobionte vertebrates such as fish and amphibians, they are found exclusively in cave waters or similar and mostly related karst waters .

threat

Today, stygobiont species are impaired by anthropogenic interference in their habitat. Major impairment paths are, for example, groundwater use (pumping out) and groundwater pollution. An important role is played by a reduction in the oxygen content due to increased biomass inundation and clogging ( colmation ) of the gap system due to fine-grained material that has washed in. The effects are hardly known in detail and are often still ignored during use. Because of their way of life, stygobionts are particularly sensitive to changes in their habitat of all kinds and are hardly able to restore their previous colonization after disturbances.

swell

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

Individual evidence

  1. ↑ Wilfried Schönborn, Ute Risse-Buhl: Textbook of Limnology. Schweizerbarth Verlag, Stuttgart 2nd edition 2013. ISBN 978-3-510-65275-4 , p.25
  2. ↑ a b D. M. Akob & K. Küsel (2011): Where microorganisms meet rocks in the Earth's Critical Zone. Biogeosciences 8: 3531-3543. doi : 10.5194 / bgd-8-2523-2011
  3. ↑ Review in GM Gadd & JA Raven (2010): Geomicrobiology of eukaryotic microorganisms, Geomicrobiology Journal 27: 491-519. doi : 10.1080 / 01490451003703006
  4. ↑ Novarino, G., Warren, A., Butler, H., Lambourne, G., Boxshall, A., Bateman, J., Kinner, NE, Harvey, RW, Mosse, RA and Teltsch, B. (1997) : Protistan communities in aquifers: a review. FEMS Microbiology Reviews, 20: 261-275. doi : 10.1111 / j.1574-6976.1997.tb00313.x (open access)
  5. ↑ Wilfried Schönborn, Ute Risse-Buhl: Textbook of Limnology. Schweizerbarth Verlag, Stuttgart 2nd edition 2013. ISBN 978-3-510-65275-4 , p.27
  6. ^ PJM Greenslade (1983): Adversity Selection and the Habitat Templet. The American Naturalist Vol. 122, No. 3: 352-365.
  7. ↑ a b David C. Culver, Tanja Pipan: Subterranean Ecosystems , p. 53
  8. ^ WF Humphreys (22009): Hydrogeology and groundwater ecology: Does each inform the other? Hydrogeology Journal 17: 5-21. doi : 10.1007 / s10040-008-0349-3