The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
The global range of M. margaritifera is Holarctic. Although it is widely distributed throughout Europe it is more common in the north and absent from the
Mediterranean region. Large populations still occur in western Russia but elsewhere the species has declined, and it continues to decline. Living populations in Britain are restricted to north and west of a line roughly from Plymouth to Hull. Recent studies have shown that there has been a dramatic
and sustained decline in the number of ' reproductively functional' populations and that this decline is especially evident in England where it is now a ' rare' species.
There is a single post-1965 record of the species living in the River Tamar (from SX38 in 1973). From the River Camel there is only an unsubstantiated 19th century record. Re-examination of voucher specimens has shown that some reports from the River Tamar pre- and post-1965 result from misidentification. Other records cannot be checked because no specimens were retained. During 2001 dead shells were found at two sites within SX37Z on the banks of the River Tamar. A recent detailed survey (commissioned by ERCCIS, funded by the Environment Agency) found no evidence that M. margaritifera still occurs in the River Tamar, so it is probably now extinct in Cornwall.
Habitat & Ecology
A filter feeder that lives wedged or partly buried in gravel and cobbles on the beds of fastflowing, soft-water rivers.
Not applicable because locally extinct.
Listed as Vulnerable by the IUCN on the global Red List; listed in Annexes II and IV of the EC Habitats Directive and Appendix II of the Bern Convention; fully protected under Schedule 5 of the WCA 1981 (for killing and injuring only); UK Biodiversity Action Plan priority species.
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.