In this study, we assess the impacts of future climate and land-use in the Beça River (northern Portugal) under different scenarios and how this will translate into the conservation status of the endangered pearl mussel Margaritifera margaritifera (Linnaeus, 1758). This species is currently present in several stretches of the Beça River that still hold adequate ecological conditions. However, the species is threatened by projected declines in precipitation for the 21st century, with implication on the river flows and water depths that might decrease below the species requisites. This situation could be especially critical during summer conditions since the ecological flows may not be assured and several river stretches may be converted into stagnant isolated pools. The habitat connectivity will also be affected with reverberating effects on the mobility of Salmo trutta, the host of M. margaritifera, with consequences in the reproduction and recruitment of pearl mussels. In addition, human-related threats mostly associated with the presence of dams and an predicted increases in wildfires in the future. While the presence of dams may decrease even further the connectivity and river flow, with wildfires the major threat will be related to the wash out of burned areas during storms, eventually causing the disappearance of the mussels, especially the juveniles. In view of future climate and land-use change scenarios, conservation strategies are proposed, including the negotiation of ecological flows with the dam promoters, the replanting of riparian vegetation along the water course and the reintroduction of native tree species throughout the catchment.

The winter of 2009/2010 was particularly severe in Northern Portugal resulting in higher river flow levels. A study was undertaken to assess the impact of this situation on several populations of freshwater bivalves (e.g., Anodonta anatina, Corbicula fluminea, Margaritifera margaritifera, Potomida littoralis and Unio delphinus) in the catchments of the Rivers Minho, Douro, Tâmega, Tua and Sabor. Massive die-offs occurred for all species in all rivers, resulting in the removal of great numbers and biomass from the riverbed to the adjacent riverbanks, reaching maximum values of 2280 individuals.m−2 and 10 225 g wet weight.m−2, respectively. The invasive Asian clam C. fluminea had both highest density and biomass (however, this invasive bivalve is not dominant in several surveyed sites, and some rivers are still not colonized by this species). Results show that the quantitative and qualitative importance of this carrion transfer to the riverbank should be incorporated in future studies on the assessment of ecosystem function, contributing to a better understanding of the role of freshwater bivalves as resource pulses in adjacent terrestrial habitats. Some of the affected species have conservational importance and these extreme climatic events are predicted to increase in the future. These massive die-off events should be incorporated into management plans and selected restoration measures such as rapid relocation of endangered native mussels back to the riverbed can be easily applied to lessen possible impacts.