Overview

This European Standard provides guidance on monitoring populations of freshwater pearl mussel Margaritifera margaritifera and the environmental features on which this species depends. Pearl mussels are endangered throughout their Holarctic range as a result of intensive land-use, pollution, river engineering, abstraction, declining populations of host fish, and exploitation by pearl fishers. Throughout this document, use of the term Margaritifera refers only to the species Margaritifera margaritifera (Linnaeus, 1758). Within the EU, Margaritifera is protected under national legislation as well as by the EC Habitats Directive (Council Directive 92/43/EEC) which requires Special Areas of Conservation to be designated to safeguard this species. The presence of a population of Margaritifera with full juvenile recruitment is the sign of a healthy functioning river. Margaritifera has a well-documented but complicated life history, with a larval glochidial stage dependent on a salmonid host. The larvae encyst within the host fish gills following release of glochidia in summer or early autumn. There they overwinter and grow before dropping off in the following spring or early summer. The few that survive initially remain buried in the river-bed substrate for several years where they interact with interstitial water. Older mussels typically have their siphons exposed to filter within the open water. The glochidial and juvenile stages are more demanding of a high-quality environment than adult mussels, emphasizing the importance of defining and maintaining appropriate ecological conditions for the young stages. Margaritifera lives for an unusually long time - over 100 years in much of its range - but life spans can be much shorter at the southern extreme of its range and much longer at the northern extreme. A lack of recruitment of young mussels leads to populations becoming unsustainable, but these problems can be masked by the continued survival of older mussels for many years long after successful recruitment has ended. The requirement for a host salmonid fish to carry the mussel larval stage presents an added challenge in maintaining the condition of freshwater pearl mussel populations. Although Margaritifera is highly demanding in river substrate and water quality, it occurs in a wide range of catchments from small, siliceous, oligotrophic rivers, often with a lake upstream, to large lowland mineral systems. This draft standard strives to encompass the range of latitudinal and geological factors that affect Margaritifera across its range. It is essential to take into consideration the unique pressures on each individual population when setting priorities for monitoring. A limited number of key references are given in the Bibliography. A comprehensive list can be consulted by using the following link to the website of the Freshwater Biological Association - http://www.fba.org.uk/cen-pearl-mussel-standard-development-reference-list. The applications of the standard include the provision of site-level data that will contribute to reporting under the Habitats Directive (Article 17, http://bd.eionet.europa.eu/article17/reference portal), undertaking environmental impact assessment, and restoring pearl mussel populations. The preparatory work has been carried out by Working Group "Biological processes" (WG 2) of CEN/TC 230, under the direction of BSI (secretariat: United Kingdom).

Responsible national committee

NA 119-01-03-05-06 AK - Biological-ecological water examination  

Responsible european committee

CEN/TC 230/WG 2 - Biological methods co-ordination group