Invertebrate Assemblages Associated with Plant Debris in a Backwater of a Mountain Stream: Natural Leaf Packs vs. Debris Dam

ABSTRACT

The invertebrate assemblages associated with two types of plant-debris accumulations, a debris dam and natural leaf packs, were studied in a backwater of a low-order Austrian mountain stream, during the spring-summer snowmelt period of flooding. The two types of debris accumulations differed significantly mainly in the proportion of fine particulate matter (< 1 mm), with consistently higher amounts in the debris dam compared with natural leaf packs. Taxon richness was significantly higher in natural leaf packs than the debris dam. The two types of habitat patches supported considerably different invertebrate assemblages, with a dominance of macrobenthos in natural leaf packs and meiobenthos in the debris dam. The results obtained for functional feeding groups support the idea that lentic debris dams act mainly as retention devices and emphasize the importance of natural leaf packs as a food source and habitat for shredders (chiefly Plecoptera).