**4.3 Ecological impacts of declining Unionid populations**

Freshwater mussels are declining in both species richness and abundance, which can reduce their influence on ecosystem functioning and have multiple negative impacts on the ecosystem as a whole. If unioniddiversity declines but total abundance remains the same, these ecological functions should continue being performed if all mussel species perform these functions at equivalent rates (i.e. are functionally redundant). However, both common and rare species are in decline (Vaughn, 1997; Vaughn & Taylor, 1999), and it has been shown that some mussel species are more effective in carrying out the ecosystem functions described above (McCall et al., 1995; Vaughn et al., 2007). It is likely, therefore, that the ecological functions performed by freshwater mussels will continue to decline along with mussel populations, which can significantly impact the overall ecological functioning of freshwater systems (Vaughn, 2010).
