Dataset of a flow intermittency study: Benthic communities of 13 alpine intermittent rivers.

In the last few decades, perennial mountain streams are becoming increasingly intermittent, due to global climate change and anthropogenic pressures. This phenomenon leads to negative effects on benthic communities' biodiversity and river ecosystems functionality. However, the impact of flow intermittency in previously perennial Alpine streams is still poorly investigated. This dataset consists of all the data collected during a spring sampling campaign performed in April-May 2017 along 13 mountain streams located in the SW Italian Alps. These watercourses have been selected because it was possible to identify two different sampling sites: one perennial, where water has always been flowing throughout the years, and one intermittent, which showed flowing water during the sampling campaign but, in the last decade, has experienced summer dry phases. All the sites have been characterized defining the microhabitats in which samples were retrieved, and physico-chemical data were collected at each site. Biological sampling included benthic macroinvertebrates and diatoms. Therefore, the present dataset offers various biological, ecological and physico-chemical information regarding Alpine streams which have recently become intermittent. Potentially, it could be used for comparisons with different benthic communities present in mountain rivers worldwide which are facing drying events too. The broad range of information present in this dataset offers the possibility to examine only the perennial sites themselves, as an example of good river functionality due to continuous flowing water, or only the intermittent ones, to better understand the effects of drying events on these peculiar ecosystems.

Diet and trophic niche of the invasive signal crayfish in the first invaded Italian stream ecosystem.

The occurrence of the signal crayfish Pacifastacus leniusculus in the Valla Stream was the first established population of this invasive species recorded in an Italian stream ecosystem. We evaluated the seasonality of diet and trophic niche of invasive signal crayfish in order to estimate the ecological role and effects on native communities of the stream ecosystem. We studied the differences in food source use between sexes, life stages and seasons using carbon and nitrogen stable isotope analyses. To supplement stable isotope analyses, we evaluated food source usage using traditional stomach content analysis. We tested the hypothesis that juveniles have a different diet, showing different trophic niches, compared to adults. Results indicated that signal crayfish adult and juvenile diets mainly rely on macroinvertebrates and periphyton in summer, shifting to mostly periphyton in autumn. Although the two age classes occupied an equivalent trophic niche, juveniles showed slightly different carbon isotope values, suggesting a somewhat ontogenetic shift consistent among seasons. No significant differences were found in adult and juvenile diets between summer and autumn seasons. Our findings suggest that signal crayfish juveniles and adults exhibited seasonal feeding habits, probably due to ecological behaviour rather than food resource availability, and that both are likely to impose similar effects on macroinvertebrate communities in this and similar stream ecosystems.