Structure, functional organization and biological traits of macroinvertebrate assemblages from leaf-bags and benthic samples in a third-order stream of Central Apennines (Italy)

Information on both structure and functions is essential to evaluate the ecological integrity of streamecosystems and their response to natural and anthropogenic disturbance. Leaf-bags have been widelyemployed to assess stream ecosystem processes and the degree of leaf mass consumption has been pro-posed as one of the most useful functional descriptor in aquatic environments. However, the breakdownrate of leaves has been compared with structural indicators of macroinvertebrate assemblages derivedfrom leaf-bags or from benthic samples, without any direct comparison on the characteristics of com-munities sampled with the two methods. The main objective of the paper is to conduct a comparativeanalysis of the structure, functional organization and biological traits of macroinvertebrate assemblagesfrom artificial leaf packs and from benthic samples of a third-order stream in the Central Apennines(Italy).Of the 43 macroinvertebrate taxa globally found in our survey, 9 showed low ability or scarce attitudeto colonize leaf-bags, while 6 rare taxa were exclusively sampled in artificial leaf packs. Both assemblageswere characterized by the dominance of Chironomidae, though they were more abundant in leaf-bags(71% of total individuals collected) than in benthic samples (44%). Conversely, the mayfly Baetis sp. com-prised more than 17% of total individuals collected with Surber nets and only 5% of leaf-bag assemblages.We found that compared to benthic assemblages, leaf-bag communities were less diversified with alower richness and a lower number of Ephemeroptera, Trichoptera and Plecoptera (EPT) taxa; significantdifferences also emerged in assemblage composition.Contrary to what expected, artificial leaf packs resulted not particularly attractive for shredder orga-nisms and were mainly colonized by collectors. Also the biological trait profiles of the leaf-bag communitywere significantly different from those shared by resident benthic taxa.Our findings could have profound implications in the assessment of the structural and functionalintegrity of stream ecosystems and in studies on freshwater biodiversity and ecosystem functioning.In these studies, the two methods (leaf-bags and Surber nets) should be regarded as complementary andnot alternative.