Ecological status of a Margaritifera margaritifera (Linnaeus, 1758) population at the southern edge of its distribution (River Paiva, Portugal)

Current and Future Ecological Status Assessment: A New Holistic Approach for Watershed Management

The Paiva River catchment, located in Portugal, integrates the Natura 2000 network of European Union nature protection areas. Resorting to topography, climate and land-use data, a semi-distributed hydrological model (Hydrological Simulation Program–FORTRAN) was run in order to simulate the hydrological cycle of the river and its tributaries. The model was calibrated over a 25-year period and validated within a 31-year period. Its performance was verified by comparing the recorded and simulated daily flows. The values of the Nash–Sutcliffe coefficient of efficiency of 0.95 and 0.76, and coefficient of determination of 0.95 and 0.82, were achieved for calibration and validation, respectively, thus showing a quite satisfactory model performance. Subsequently, the climate change impacts on temperature and precipitation, as well as their extremes, and on the flowrates were also assessed for a future period (2041–2070) under two anthropogenic forcing scenarios (representative concentration pathways 4.5 and 8.5). A procedure for selecting the most relevant metrics for assessing the ecological condition of the Paiva River was developed based upon a set of 52 invertebrate families sampled. Correspondence analyses were carried out for biological datasets (traits/metrics) with physicochemical and land use/land cover matrices separately. Out of all variables, water quality and flow and agriculture land use explained most of the variance observed. The integrated analysis undertaken in the present study is an important advance when compared to previous studies and it provides key information to stakeholders and decision-makers, particularly when planning suitable adaptation measures to cope with changing climates in the forthcoming decades.

A tale of shells and claws: The signal crayfish as a threat to the pearl mussel Margaritifera margaritifera in Europe

The freshwater pearl mussel Margaritifera margaritifera is a highly threatened species in Europe. Several mechanisms may be responsible for the decline in distribution and abundance of European pearl mussel populations, but almost no quantitative data exists about the possible negative impacts of invasive alien species (IAS). In this study, we clearly demonstrate that the invasive signal crayfish Pacifastacus leniusculus predates pearl mussels, using a laboratorial experiment followed by in situ validation in four rivers in the North of Portugal (Mente, Rabaçal, Tuela and Baceiro Rivers; Douro Basin). In the laboratory, the crayfish had a clear preference for small-sized pearl mussels but no differences in predation were found in mesocosms with and without sediment. In addition, we clearly demonstrated that the signal crayfish predates pearl mussels in natural conditions and detected a significant density dependent effect (i.e., sites with more crayfish presented higher number of pearl mussel shells with marks of predation). Given the recent introduction of the signal crayfish and the potential negative impacts on pearl mussel populations we also investigated its autoecology (distribution, abundance, size structure and sex-ratio) in the four studied rivers. Significant differences in average abundance and size of the crayfish were detected between sites and the sex-ratio was highly skewed to females. In view of the widespread distribution of signal crayfish (and other invasive crayfish species) in Europe, future management actions devoted to the conservation of pearl mussels should take in consideration the possible negative effects of these predators, especially on juveniles.

The role of calcium concentration in the invasive capacity of Corbicula fluminea in crystalline basins

The natural variation of environmental factors in freshwater basins determines their biodiversity. Among them, calcium is a key physiological compound for freshwater invertebrates. It is required for shell formation, muscle contraction, it mediates gene expression and allows counteracting acidosis during stress periods, among other functions. Although the distribution of different freshwater species has been suggested to be linked with the environmental calcium concentration, as yet, no research studies have confirmed this. Identifying whether environmental calcium concentrations might determine the invasion success of alien species would be critical in developing and implementing effective management strategies to control them. Here, a multidisciplinary approach integrating field surveys, analytical chemistry techniques, molecular biology analyses and a lab-scale experiment was taken to decipher whether the environmental calcium concentration might hamper the establishment of Corbicula fluminea in northwestern Iberian rivers. A Principal Component Analysis on water chemistry variables from 13 water bodies identified environmental calcium concentration, among others, as one key factor that best characterized the distribution area of C. fluminea. The calcium content in animals' bodies from two representative rivers was dependent on the environmental calcium concentration of freshwater basins; the lower the concentration, the lower the body's content. The expression of stress- and calcium homeostasis-related genes was higher in C. fluminea from low calcium concentration environments than in those from calcium-rich freshwater basins. Finally, under experimental conditions, lower water calcium concentrations decreased C. fluminea growth rates. The present data suggest, for the first time, that environmental calcium concentration may act as a determinant factor on the invasion success of C. fluminea in freshwater environments. Our results provide new clues for the identification of basins with increased risk of potential invasion by C. fluminea based on environmental calcium levels.

Impacts of climate change and land-use scenarios on Margaritifera margaritifera, an environmental indicator and endangered species

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.