Synopsis of the European Freshwater Mussels: Pseudunio auricularius (Spengler, 1793), the Giant Freshwater Pearl Mussel

Here, we present a synthesis of the available knowledge on the Giant Freshwater Pearl Mussel Pseudunio auricularius (= Margaritifera auricularia) (Spengler, 1793). We also identify critical knowledge gaps that require attention for effective conservation guidance and species recovery. Pseudunio auricularius is one of Europe’s most endangered invertebrate species, with its range having been reduced by over 90% in the last two centuries. Long thought to be extinct, it was rediscovered in Spain and France in the 1990s–2000s, but these populations are in a very critical situation. Pseudunio auricularius lives in gravelly, stable and well-oxygenated sediments. Larvae (glochidia) attach to fish gills to complete their life cycle. The primary host fish, the Atlantic sturgeon Acipenser sturio, now extinct in European rivers, Salaria fluviatilis in Spain and Petromyzon marinus in France, are threatened. Other stressors are the deterioration of mussel habitats and water quality, climate change and invasive species such as Corbicula spp. The earliest life stages are most vulnerable, further ecological studies are urgently needed. Monitoring and conservation measures such as captive breeding will continue in both countries. Catchment-wide restoration of river morphodynamics and water quality is needed to allow the re-establishment of this emblematic species and its host fishes.