Collapse of native freshwater mussel populations: Prospects of a long-term study

Freshwater biodiversity is under threat, but long-term quantitative studies showing major demographic declines in invertebrate species are still scarce. Here we focus on a long-term study (2004 to 2019) using four native freshwater mussel species (Order Unionida) colonizing two canals of the Ebro River (Spain). Special attention was given to Pseudunio auricularius (Spengler, 1793), a critically endangered species. Generalized linear mixed models results showed significant temporal effects on mussel densities, with a continuous decline in all species present, being Anodonta anatina, Potomida littoralis and Unio mancus now considered locally extinct. Pseudunio auricularius is still present in the studied canals, but at very low densities (0.01 ind/m2). Capture-recapture data on P. auricularius show a progressive decline in its survival probability, down to 0.15 in 2020 in the Canal Imperial de Arag ' on, although in the Canal de Tauste it remains close to 1. Based on these results, we discuss several hypotheses that may explain this rapid collapse of unionid populations. Given the precarious conser-vation status of freshwater mussels in both canals, effective management measures should be urgently applied, including habitat restoration and captive breeding.

Automated summary

Freshwater biodiversity is at risk, and the decline of invertebrate species is not well-documented. This long-term study in Spain examined four native freshwater mussel species and found significant declines in mussel densities, with three species locally extinct. The critically endangered species, Pseudunio auricularius, showed a decline in survival probability, highlighting the urgent need for conservation measures.