Flow intermittency negatively affects three phylogenetically related shredder stoneflies by reducing CPOM availability in recently intermittent Alpine streams in SW-Italian Alps

Abstract

Several Alpine streams are currently facing recurrent summer drying events with detrimental consequences on stream detritivores, i.e., shredders, due to negative effects via changes the organic matter (CPOM) availability. We examined the ecological requirements of three phylogenetically related shredder genera belonging to the family of Nemouridae (Plecoptera), namely Nemoura, Protonemura and Amphinemura, in 14 Alpine streams recently facing recurrent summer flow intermittency events. We evaluated the overlap among their ecological niches measured in terms of hydraulic stress, substrate composition, changes in CPOM availability and competition with other shredder taxa (i.e., presence of individuals of other shredders) and we examined potential changes in their ecological niches between permanent and intermittent sites. The ecological niches of Protonemura and Amphinemura overlap broadly, but not with Nemoura, suggesting only partial potential competition. The reduced CPOM availability decreased the individual abundance of the three genera in intermittent sites, where they consistently preferred microhabitats with high CPOM availability and low competition with other shredder taxa, possibly due to food limitation. Overall, our results emphasize how the negative effect of flow intermittency on shredders in Alpine streams is mainly due to the decrease in CPOM availability, with consequent potential bottom up effects on stream ecosystem functionality.

Seasonal and functional variation in the trophic base of intermittent Alpine streams

“…Here, it is interesting to note that Nemouridae have no results in highly intermittent streams in summer and autumn, perhaps reflecting a complete exclusion from drying sites due to their high degree of rheophily (Tachet et al 2010). Nemouridae are also often described as shredders (Piano et al 2020), although the high degree of reliance on periphyton we estimated (> 50% in spring) suggests that the high‐altitude species sampled here are facultative rather than obligate consumers of terrestrial organic matter. Nemouridae may therefore feed on algae in spring when competition with other rheophilic grazers (i.e., Ephemeroptera) is low, switching to leaf litter during peak abscission periods in autumn.…”

Long-lasting effects of experimental flow intermittency on alpine stream macroinvertebrates (Val Roseg, Switzerland)

“…Functional feeding traits could explain some of the shifts we observed in macroinvertebrate assemblages: shredder (Limnephilidae) and scraper (Heptageniidae) densities were lower and generalist collector gatherer (Chironomidae) densities were higher in the RC compared to the MC. Studies from other flow experiments in alpine intermittent streams found similar results (Piano et al, 2019(Piano et al, , 2020Siebers et al, 2020). The change in feeding mode could be mediated by a shift in basal resource quality in stream food webs; e.g., reduced microbial conditioning of terrestrial organic matter in drying alpine streams could lead to lowered lability for stream macroinvertebrates, or drying could reduce the productivity of algae in biofilms (Niedrist & Füreder, 2017;Siebers et al, 2019).…”

Effects of antecedent drying events on structure, composition and functional traits of invertebrate assemblages and leaf‐litter breakdown in a former perennial river of Central Apennines (Aterno River, Abruzzo, Central Italy)

“…Similar results were obtained by Piano et al (Piano, Doretto, Falasco, Fenoglio, et al, 2019; Piano, Doretto, Falasco, Gruppuso, et al, 2019) in Alpine streams and Datry et al (2011) in French Mediterranean rivers. In addition, Piano, Doretto, Falasco, et al (2020) demonstrated that in Alpine streams, recurrent seasonal droughts significantly altered CPOM availability, reduced shredder biodiversity and induced a shift in the ecological niche of some shredder species with consistent bottom‐up effect on the whole stream functionality. Although we did not directly assess the quantity of CPOM at P S and II S , we can reasonably assume that during the period of investigation a similar input of foliar material characterized both sites.…”