Potential use of beaver Castor fiber L., 1758 dams by the thick-shelled river mussel Unio crassus Philipsson, 1788

ABSTRACT

The objective of this paper is to draw attention to a previously unrecognised habitat for Unio crassus Philipsson, 1788 (Bivalvia: Unionidae), namely beaver dam-and-pond complexes. The construction of beaver ponds will allow the colonisation of high energy streams by providing flow refuges during periods of high near-bed shear stress. The absence of freshwater mussels (Unionidae) in mountain streams may result from steep slopes, shear stress during floods, lack of food suspended in the water column (seston), and unfavourable conditions for the settlement and growth of juvenile mussels. Transportation of parasitic larvae on host fish is the main dispersal mechanism for the mussels. A possible constraint on the colonisation of beaver complexes by freshwater mussels is that beaver dams may hinder the upstream movement of their minnow hosts. In the surveyed beaver ponds, the first specimens of U. crassus were found in 2008. Single mussels were also found in subsequent years. It is uncertain whether the occurrence of U. crassus depends on the periodic support of the population from the main river, but the presence of beaver ponds is certain to have given it the opportunity of colonising new areas.

KEYWORDS:

• Beaver dam-and-pond complex
• endangered species
• freshwater bivalves
• mountain stream
• river
• Unionidae

Acknowledgements

We would like to thank the editors and two anonymous reviewers for their constructive comments and suggestions which helped us improve the paper. We are grateful to A. Wojton, S. Tabasz and our students for their help in part of the field work. Funding of this work was partially provided by a grant from the Ministry of Science and Higher Education of Poland (No. N/N304/1163/33).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Funding of this work was partially provided by a grant from the Ministry of Science and Higher Education of Poland; Komitet Badań Naukowych (No. N/N304/1163/33).