Freshwater pearl mussel
Margaritifera margaritifera
The freshwater pearl mussel ( Margaritifera margaritifera ) is a large freshwater mussels, which applies in Germany of the early 21st century as an endangered species.
Artbesonderheiten and development
The freshwater pearl mussel can reach an age of up to 280 years according to the latest results. Size and age to the north to take out, it is in Spain usually only 8-10 cm tall and about 60-70 years old, while it is up to 280 years old and 14 inches tall in Sweden. Their proliferation is a more complex since. Bound to demanding conditions, failure-prone process with several intermediate stages After the tiny early stages ( glochidia ) are hatched the shell, they need as a host brook trout, in their Gills area they live parasitically ten months; other fish species are not suitable as a host. They grow from about 0.05 mm to 0.5 mm wide zoom Jung shell. Around May, when the temperature and the stream bed are consistent, they drop on a body of water in the river bed between the pebbles and stones and dig there a. There they live hidden and only come after about seven years, in the adult stage, and with the now formed hard shell on the surface of the water bottom. Then spend the rest of their lives largely stationary. In the flow they allow the water to flow through their gills and filter food particles out there. In ecologically intact environment, the freshwater pearl mussel forms colonies.
It designates the major river molluscs, including pearl mussel, also known as naiads.
Distribution area and history
The freshwater pearl mussel is found almost all over the northern hemisphere, in Europe, for example, from Spain to northern Scandinavia ( Arctic Circle ).
Known larger populations in Germany were up to industry -induced strong river water pollution both in Saxony ( eg in Pulsnitz ), in Bavaria (eg, in the rain, the Southern Regnitz and the Perlenbach ) and in North Rhine -Westphalia (eg example, in named after them Perlenbach in the Eifel ).
At the time of the small German states and princely courts until the 18th century it was partially targeted settled and effectively (eg, chopping off the hand) protected with draconian penalties, as in the Odenwald and in the Eifel detectable. The right to search for pearls was called Perlregal. From 300 years ago Perlmuschelbänke with more than a thousand animals per square meter are known.
With the French invasion of 1794 Perlregal went out in many parts of Germany, which was made possible overexploitation. The most significant occurrence in the Czech Republic is the upper reaches of the creek Jankovský.
It contained only a few shells actually beads: These data range from 0.05 % to 4% ( a bead on 2,000 or 25 shells ).
Today's occurrence in Germany
The freshwater pearl mussel is now very rare in Germany. Reasons for the population decline are:
- Water pollution caused by over-fertilization with sewage and salt
- Silting of streams
- Displacement of brook trout, which serves as host of the mussel, introduced by the rainbow trout
- Extinction of the salmon, which serves as the host animal
- Destruction of entire holdings by Pearl robbers in ancient times
- New predators by the invasive species muskrat and raccoon
In Germany are still deposits in Bavaria, North Rhine -Westphalia, Saxony, Rhineland -Palatinate and the Lüneburg Heath to find.
In Bavaria, the mussel originally focused on three areas from which the Bavarian Forest and Upper Franconia still have meaning today. In the Upper Palatinate, there are only small residual populations. The Bavarian Forest is the area of the left Danube flows between Regensburg and Passau is to call, the catchment areas of rain and Ilz in the former Bishopric of Passau have provided particularly rich returns. A special feature of the last occurrence dar. on sandstone in the Schondra ( Bavaria )
The proven reserves by 2008 in the Vogelsberg and Rhön in Hesse seems extinguished, however, the species is in the region officially considered lost, maybe they became extinct here.
In Lutter - a river in the Lüneburg Heath - were recorded at the nature conservation project " Lutter " successes in the conservation of the freshwater pearl mussel. The stock listed above, the only one in the whole of Europe, a positive development. For the first time in 1985, the Lutter caught brown trout infected with freshwater pearl mussel larvae and in the stream is reset. However, these initial measures were initially without success. The cause lay in the unnaturally high sand load of Lutter, a thing you noted later. The scientific substantiation by Buddensiek ( 1991) and the confirmation in practice by Abendroth (1993 ) led to the breakthrough. In 2008, more than 12,000 shells were detected again.
In Rhineland -Palatinate, there are endangered stocks in the Our ( Eifel, 100 to 200 animals) and the Nister (Westerwald, known 26 copies). The stock in the Nister was rediscovered. The animals are 60 years and older. A natural increase could not be detected thus for 60 years. Both of Our Nister and there are efforts to support proliferation through the bringing together of glochidia and host fish in tanks.
Worldwide threat
After the classification of the IUCN kind in the world is considered endangered ( endangered ) (as of 1996), with the actual situation is insufficiently known. Because of their distribution exclusively in densely populated Europe, it is next to water pollution and the factors listed above, also threatened due to the preference for lime- streams at the same time fairly high lime requirement for the shell by water acidification by acid-acting industrial and car exhaust also in otherwise clean and natural waters.
Legal protection status
The freshwater pearl mussel is under federal protection of species regulation by a Federal Nature Conservation Act strictly protected species
In addition, it is a species in Annex II and Annex V of the Habitats Directive.