River mussel
| River mussel | ||||||||||||
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River mussel ( Unio crassus ) |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Unio crassus | ||||||||||||
| Philipsson , 1788 |
The river mussel , also Common or Small river mussel ( Unio crassus ), is in fresh water , rarely in brackish living mussel . The name brook mussel became common when it became clear in the 1980s that this species was almost only to be found in the upper reaches of the waters. However, the species was originally widespread as far as the major river systems of the Elbe , Rhine and Danube and can still be found in large rivers in Northern Europe. Therefore, the name river mussel is described as misleading by some specialists. In Germany, however, evidence of vital and reproductive populations of this species is currently (2009) limited to smaller river systems and streams.
distribution
With the exception of the British Isles, it lives in almost all of Northern and Central Europe , also in Eastern Europe, but not east of the Urals or Asia Minor. It does not occur in the tributaries of the Mediterranean , although it is unclear whether it can be found in the Iberian Peninsula . It sometimes lives in areas higher than 600 meters.
anatomy
Like all mussels, the river mussel has a shell with two valves and a strong sphincter. The bowl can be up to 10 cm long. The gills are used for breathing and the absorption of suspended matter in the water. In females there are so-called marsupia in the gills, breeding spaces for spawning or larvae. The foot of the river mussel is relatively strong, it is used for locomotion and for digging. In the case of the buried river mussel, however, the breathing opening always protrudes from the ground.
Reproduction
At 3–4 years (according to other authors 4 to 5 years), river mussels are sexually mature and remain reproductive for almost their entire life. However, fertility in old populations decreases sharply; there are hardly any young mussels to be found. Spring to early summer is the breeding season. The males release the sperm into the water, where it is ingested by the females through the gills. The female's spawn is located in so-called marsupia , which are also located in the gills. The development of the larvae can vary between 3 and 6 weeks, depending on the water temperature. Between April and the beginning of August at the latest, normally at the end of July, the larvae are released from the gills individually or in groups, then they settle as parasites as approximately 0.2 mm glochidia in the gills of certain fish species. Particularly suitable host fish are chub , minnow , and rudd ; Aland , bullhead , stickleback and nose may be suitable . Depending on the temperature and host fish species, the glochidia in the gills develop into finished young mussels within 350–930 days . The juvenile mussels leave the gills and dig into the substrate, where they spend 1–3 years before they reappear on the substrate surface as adult mussels.
Hazard and protection
The river mussel was a very common species until the beginning of the 20th century, but then declined very quickly. In addition to natural enemies such as the muskrat (which, by the way, has also been naturalized by humans), the main causes are artificial fertilizers. B. be introduced into the water via drainage. In some federal states around 90% of the population was exterminated. The remaining populations often consist predominantly or even completely of older animals (compared to the achievable age of the respective population). On the other hand, young mussels are almost completely absent from these stocks and therefore losses through mortality are no longer or only insufficiently compensated. The offspring in captivity is successful, which is why young animals or fish with larvae in their gills are repeatedly released. However, it is difficult to verify the success of these measures.
The river mussel is a species according to Annex II and IV of the Fauna-Flora-Habitat Directive and is therefore protected throughout the EU. In addition, it is a special and strictly protected species in Germany under the Federal Nature Conservation Act. In addition, it is also subject to the state fisheries laws, which define a year-round closed season .
In the International Red List ( Red List of Threatened Species ) of the IUCN ( International Union for Conservation of Nature; officially International Union for Conservation of Nature and Natural Resources; German International Union for the preservation of nature ) the species was in 2011 from the category lower risk / near threatened (= warning level) increased to endangered (= endangered). In the Red List of Austria the species is classified as "critically endangered" (CR).
Systematics
From a taxonomic point of view, the species is poorly processed. In Germany alone, however , a distinction is made between at least three subspecies , with shell characteristics and geographical distribution serving as diagnostic features.
- Unio crassus crassus
- Unio crassus riparius
- Unio crassus cytherea
Unio crassus nanus and Unio crassus forma maximus are also mentioned in current literature . Possibly other subspecies exist as local forms.
Individual evidence
- ↑ Common river mussel - Mollusk of the year 2006 . medienwerkstatt-online.de. January 11, 2007. Retrieved May 11, 2011.
- ↑ a b Species profile of the river mussel Unio crassus (Philipsson, 1788) (PDF; 701 kB) hmulv.hessen.de. Retrieved September 24, 2018.
- ↑ a b Jens-Eike Taeubert, Ana Maria Posada Martinez, Bernhard Gum and Jürgen Geist: The relationship between endangered thick-shelled river mussel (Unio crassus) and its host fishes. In: Biological Conservation. No. 155, 2012, pp. 94-103.
- ↑ a b Hochwald, S .; Gum, B .; Rudolph, BU; Sachteleben, J. 2012: Guideline for river mussel protection. Ed .: Bavarian State Office for the Environment (LfU), Augsburg
- ^ Federal Ministry for Agriculture, Forestry, Environment and Water Management (Ed.): Red Lists of Endangered Animals Austria. Checklists, risk analyzes, need for action. Part 2: reptiles, amphibians, fish, moths, molluscs Böhlau Verlag, Vienna 2007, ISBN 978-3-205-77478-5
Web links
- The river mussel - mollusk of the year 2006
- V. Wiese: Atlas of land and freshwater mollusks in Schleswig-Holstein
- Unio crassus inthe IUCN Red List of Threatened Species 2013.1. Posted by: Van Damme, D., 2011. Retrieved November 22, 2013.
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