The Freshwater Pearl Mussel: A Costly Stowaway or an Important Habitat Engineer?

The freshwater pearl mussel (FPM) (Margaritifera margaritifera) has a fascinating lifecycle that includes a parasitic life stage on host fish; the brown trout (Salmo trutta) and/or the Atlantic salmon (Salmo salar) (Geist et al., Aq Conser: Mar Freshw Ecosystems. 16:251–266, 2006) in order to successfully reproduce. Freshwater mussels, including the FPM, have large effects on ecosystem functions in streams and rivers. The FPM is thus an important habitat engineer and keystone species where healthy populations indicate a well-functioning ecosystem (Geist, Hydrobiol 644: 69–88, 2010). In this chapter, our aim is to provide a general overview of the present knowledge regarding the FPM and (1) the interaction with its host fish (2) its habitat requirements, (3) the threats to the mussel, and (4) successful restoration measures.