Led by the scientist Manuel Lopes Lima, of the Centre of Investigation in Biodiversity and Genetic Resources (BIOPOLIS-CIBIO), of Porto University and the Mértola Biological Station, the study was made in collaboration with members of five other research centres (CBMA, CIMO, CIIMAR, CITAB and MARE), representing six Portuguese academic institutions – Bragança Polytechnic and the universities of Porto, Minho, Trás-os-Montes and Upper Douro, of Lisbon, and of Évora.

Freshwater mussels, a group of bivalves with over 900 species, can be found in rivers and lakes on all continents, where they were abundant and carried out an important role in the ecosystem, improving the water and substrate quality, providing a fundamental habitat for other species.

Until now, there wasn’t any data on the populational tendencies of these animals in Portugal, but through a thorough survey of freshwater mussel populations in 132 locations spread over 15 distinct drainage basins, it was discovered that the data is “dramatic and extremely concerning.”

The study shows “a general decline of 60% in a number of locations and an impressive decrease of 67% in the total abundance of freshwater mussels in Portugal over the last two decades.”

These results are in line with the observations made during the EdgeOmics project, financed by the Foundation for Science and Technology, whose objective is to evaluate and foresee the impact of climate change on these mussels.

Manuel Lopes Lima shared with Lusa that “all freshwater mussel species are in rapid decline and risk extinction in Portugal, the information is already included in the making of the most recent Red Book of Portuguese Invertebrates, where all species classified as threatened or protected are catalogued.”

Freshwater mussels generally have a long life and are “highly sensitive” to habitat unrest, thus being good indicators of the ecological integrity of freshwater ecosystems.

The investigation points to the increase of prolonged droughts, the changing of the river habitat by dams and the introduction of exotic species, such as the Asian clam, as the main courses behind the mussels’ decline.

According to the researchers, the protected freshwater mussel species in the EU are “inadequately monitored.”

“Even the species classified as common should receive more attention, as they could be improperly evaluated, as was shown in this study. This subject is particularly alarming in the Mediterranean region, where species endemism is high and freshwater habitats are severely affected by water shortage,” they stress.

To revert the “alarming populational tendency of decline,” the study emphasises “the urgent need for efficient use of water, of the implementation of restrictions on irrigation in vital biodiversity areas, of the mitigation of hydrological changes and of restoring the lost connectivity of aquatic habitats due to past physical alterations, such as dams.”

On the other hand, the study’s authors underline that “to prevent the extinction of the most critically endangered species, including Margaritifera margaritifera (Freshwater pearl mussel), Potomida littoralis (Náiade-negra) and Unio tumidiformis (Náiade-do-Guadiana), whose populations fell to almost residual levels, it’s imperative that we act with urgent conservation actions, like the establishment of reproduction programs in captivity, strict protection for the remaining populations and the large-scale restoration of habitats.”

This study was recently published in the Biological Conservation magazine.