Freshwater pearl mussels are critically endangered ecosystem engineers that require pristine, fast-flowing rivers with salmon or trout hosts for their larval development.
Freshwater pearl mussel populations that fail to reproduce because salmon hosts are absent face localised extinction as long-lived adults gradually die. The narrow habitat requirements make them highly sensitive to any catchment change. While mussel sentience is uncertain, the ecosystem engineering role they play directly benefits fish, otters and waterbirds whose welfare depends on clear, oxygenated rivers.