Freshwater pearl mussel (Margaritifera margaritifera)

GenusMargaritifera (1)
SizeLength: 12 – 15 cm (2)

Classified as Endangered (EN) on the IUCN Red List. Subspecies: Margaritifera margaritifera durrovensis is classified as Critically Endangered (CR) on the IUCN Red List (1).

One of the longest-living invertebrates in existence (2), the freshwater pearl mussel has, like all bivalve molluscs, a shell consisting of two parts that are hinged together, which can be closed to protect the animal’s soft body within (3). The shell is large, heavy and elongated (4) (5), typically yellowish-brown in colour when young and becoming darker with age (2). Older parts of the shell often appear corroded, an identifying feature of this mussel species (6). The inner surface of the shell is pearl white, sometimes tinged with attractive iridescent colours (4). Like all molluscs, the freshwater pearl mussel has a muscular ‘foot’ (3); this very large, white foot enables the mussel to move slowly and bury itself within the bottom substrate of its freshwater habitat (4) (5).

The freshwater pearl mussel can be found on both sides of the Atlantic (4), from the Arctic and temperate regions of western Russia, through Europe to north-eastern North America (2).

Clean, fast-flowing streams and rivers are required for the freshwater pearl mussel (4) (2), where it lives buried or partly buried in fine gravel and coarse sand (2), generally in water at depths between 0.5 and 2 metres, but sometimes at greater depths (4). Clean gravel and sand is essential, particularly for juvenile freshwater pearl mussels, for if the stream or river bottom becomes clogged with silt, they cannot obtain oxygen and will die (4). 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 (4).




Once the most abundant bivalve mollusc in ancient rivers around the world, numbers of the freshwater pearl mussel are now declining in all countries and this species is nearly extinct in many areas (4). The causes of this decline are not fully understood, but alteration and degradation of its freshwater habitat undoubtedly plays a central role (4). The negative impacts humans have on rivers and streams come from a wide range of activities such as river regulation, drainage, sewage disposal, dredging, and water pollution, including the introduction of excess nutrients (4). Anything that affects the abundance of the fish hosts will also affect the freshwater pearl mussel; for example, the introduction of exotic fish species, such as the rainbow trout, reduces the number of native fish hosts (4). Introduced species are also directly affecting the freshwater pearl mussel; the invasion of the zebra mussel (Dreissena polymorpha), which has been spread to new locations by being transported on the bottom of boats or in ballast waters, has impacted freshwater pearl mussel populations in all countries it has invaded (4).

The freshwater pearl mussel, which is completely protected in most European countries (9), has been the focus of a significant amount of conservation efforts (8). Measures have included the transfer of adult mussels to areas where it had gone extinct (8) (10), the culture of juvenile mussels, and the release of juvenile trout, which have been infected with glochidia, into small rivers (10), but mainly the freshwater pearl mussel has benefited from habitat restoration projects in some areas (10). Due to the essential role salmonid fish play in the life of the freshwater pearl mussel, the conservation of salmon and trout is also central in the survival of this endangered freshwater mussel (4).

For further information on the conservation of freshwater habitats and biodiversity see:

Information authenticated (01/09/09) by Dr Mark Young of Aberdeen University

  1. IUCN Red List (December, 2009)