Freshwater Pearl Mussel (Margaritifera margaritifera): An iconic specie at the risk of extinction

Editor's Notes

1. The freshwater pearl mussel (Margaritifera margaritifera) is an endangered species of freshwater mussel, an aquatic bivalve mollusc in the family Margaritiferidae
2. Once abundant throughout a geographic range spanning from North America, through Europe into Russia, the species has suffered massive declines, and is now critically endangered or extinct in many river systems where it was once common. It is listed as endangered on IUCN.
3. Freshwater mussels have three basic characteristics which distinguish them from other animals; these include 1) a two-valved shell, 2) a soft body, and 3) a muscular foot.   The “soft” parts consist of respiratory organs, digestive organs, and other vital parts.  The foot, often seen extended from between the two valves, aids the mussel in locomotion, burrowing, and positioning in the river bottom. The shiny layer inside the shell is called the nacre or “mother of pearl.”  The nacre may be white, purple, pink, or pale orange.  The outer layer is made of protein and serves to protect the shell.   Shells come in a variety of shapes, including round, elongate, oval, or tear-drop shaped.  The beak is the oldest part of the shell, and the end closest to the beak is the anterior or front.  The outer surface may be smooth or rough
4. Habitat Clean, fast-flowing streams and rivers are required for the freshwater pearl mussel,[6][9] where it lives buried or partly buried in fine gravel and coarse sand,[6] generally in water at depths between 0.5 and 2 metres, but sometimes at greater depths. Also essential is the presence of a healthy population of salmonids, a group of fish including salmon and trout, on which the freshwater pearl mussel relies for part of its life cycle.[9] Feed They feed by filtering food particles from the water column, with each adult mussel filtering up to 50 litres of water an hour. When mussels are abundant they play an important role in maintaining and improving the water quality, benefiting not just their own development, but the health of the river ecosystem as a whole. Life span Freshwater pearl mussels are a long-lived species. The average lifespan ranges from 86 to 102 years, although lifespan varies greatly with environmental factors such as water quality. The oldest freshwater pearl mussel was found to be 280 years old.
5. Pearls are a product of the defense mechanism of organic immune systems, It took decades. According to current estimates, one in a thousand mussels may include a pearl.
6. Pearls are the only jewels created by a living animal.  The quality of pearls with regard to their shape and colour, which are important factors in terms of their market value, are not only influenced by external environmental factors, but also by the inherited capabilities of individual oysters. Pearl come in a large range of colors varying from silver and white to gold, pink etc, Purple gold  and black pearl fetch the highest prices in the market. Pearl m  Pearls are a product of the defense mechanism of organic immune systems, and studies of their medicinal value have shown distinct anti-oxidant and anti-inflammatory effects. Pearls can be sphere, half sphere, oval, pear-like, spindle-like, and irregular shape.  Pearls are a product of the defense mechanism of organic immune systems, and studies of their medicinal value have shown distinct anti-oxidant and anti-inflammatory effects. Extracts from pearls have been used in variety of clinical treatments for ulceration, cataracts, and tumours.  Pearls may be processed into powdered products for skin whitening, and as calcium supplements
7. This species is a special case in having approximately 200,000,000 mature individuals but, due to habitat degradation, having very little replacement as adults die. Functional extinction is widespread throughout most of the range. Most subpopulations are isolated and genetic exchange between subpopulations is unlikely by natural means. Across most of the range adults that die will not be replaced due to habitat changes that cannot support juveniles, so most subpopulations have not recruited for many years. Overall in the last 90 years for Europe there has been a decline of 81.5%; a loss of 87% for EU countries. The overall global reduction in population size over the same period is 61.5%.
8. Freshwater pearl mussels have a complex and unusual life cycle. Sexually mature individuals breed once a year. Breeding occurs from june to July. Males releases sperms in water which is then inhaled by female mussel through incurrent siphon. They begin life as tiny larvae known as glochidia, In summer around 2.3 million glochidia are released directly into the water column by female mussels in vast numbers between August and September. Most of these glochidia perish, swept downstream by the fast flowing water, but a few are inhaled by passing salmonid fish (trout or salmon), and snap shut on a filament of the fish’s gills. Here they grow in this oxygen rich environment, getting their nutrients directly from their temporary host until it reaches around six times their original size. At this point they have developed into into young mussels, and drop off their host to begin life as a filter feeder buried in the river bed. Freshwater pearl mussels grow extremely slowly.
9. Residential & commercial development Housing & urban areas Commercial & industrial areas Tourism & recreation areas Agriculture & aquaculture Annual & perennial non-timber crops Wood & pulp plantations Livestock farming & ranching Marine & freshwater aquaculture Energy production & mining Mining & quarrying Renewable energy Transportation & service corridors Roads & railroads Shipping lanes Biological resource use Hunting & trapping terrestrial animals Fishing & harvesting aquatic resources Human intrusions & disturbance Recreational activities Natural system modifications Dams & water management/use Other ecosystem modifications Invasive and other problematic species, genes & diseases Invasive non-native/alien species/diseases Problematic native species/diseases Introduced genetic material Pollution Domestic & urban waste water Industrial & military effluents Agricultural & forestry effluents Garbage & solid waste Air-borne pollutants Excess energy Climate change & severe weather Droughts Temperature extremes Storms & flooding
10. Direct threats for adult mussels such as pearl harvesting, predation by muskrats, alien crayfish and eel (potentially feeding on juvenile mussels) have limited local influence and cannot explain the species’ global decline.
11. Instead, indirect effects connected with anthropogenic perturbations such as habitat degradation, alteration and fragmentation are probably the most important factors for decline.
12. The Freshwater Pearl Mussel Ark Project has been running at the Freshwater Biological Association since 2007.  If you’re found guilty of an offence you could get an unlimited fine and up to six months in prison.
13. To date, many pearl mussel rivers within the EU have been designated as Special Areas of Conservation (SACs), and the species is protected under national legislation with various levels of restriction. In most cases, both strategies have resulted in some improvement on direct damage such as pearl fishing, and some protection against projects like dam constructions. Part of the problem of protection of the species within SACs is the design of the directive, which restricts SACs to habitats of importance, so that buffer zones that would be of great value in conservation action cannot be part of any designation. The freshwater pearl mussel and its habitat are fully protected by law, under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) and Annex 2 of the Habitats Directive. A strong negative indicator of the future prospects of this species has been the very poor response of the various competent authorities to dealing with the damaging effects of intensification of agriculture and coniferous forestry in pearl mussel catchments.
14. Assessment of inbreeding coefficients, observed and expected heterozygosities, history of populations, effective population sizes Assessment of population uniqueness (e.g. occurrence of private alleles, genetic differentiation from other populations) Relatedness and analyses of gene flow between different (sub-)populations Avoidance/monitoring of genetic effects in captive breeding Development/availability of reliable genetic markers (e.g. microsatellites, mtDNA markers) Development/availability of non-destructive sampling techniques for living specimens (haemolymph, tissue) Genetic Conservation Prioritization for the species throughout its distribution range Testing links between genetic diversity and differentiation of pearl mussels/molluscs with co-occuring species (e.g. mussel—host fish) Decisions on genetic biodiversity hotspots/priority areas for conservation and on management tools