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 stream ecosystems and their response to natural and anthropogenic disturbance. Leaf-bags have been widely employed to assess stream ecosystem processes and the degree of leaf mass consumption has been proposed as one of the most useful functional descriptor in aquatic environments. However, the breakdown rate of leaves has been compared with structural indicators of macroinvertebrate assemblages derived from leaf-bags or from benthic samples, without any direct comparison on the characteristics of communities sampled with the two methods. The main objective of the paper is to conduct a comparative analysis of the structure, functional organization and biological traits of macroinvertebrate assemblages from 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 attitude to colonize leaf-bags, while 6 rare taxa were exclusively sampled in artificial leaf packs. Both assemblages were 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. comprised 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 a lower richness and a lower number of Ephemeroptera, Trichoptera and Plecoptera (EPT) taxa; significant differences also emerged in assemblage composition. Contrary to what expected, artificial leaf packs resulted not particularly attractive for shredder organisms and were mainly colonized by collectors. Also the biological trait profiles of the leaf-bag community were significantly different from those shared by resident benthic taxa. Our findings could have profound implications in the assessment of the structural and functional integrity 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 and not alternative. (C) 2014 Elsevier Ltd. All rights reserved.