Food, substrate or both? Decomposition of reed leaves (Phragmites australis) by aquatic macroinvertebrates in a large shallow lake (Lake Balaton, Hungary)

The aim of this study was to investigate the use and decomposition of reed leaves (Phragmites australis) by aquatic macroinvertebrates in a lake environment (Lake Balaton, Hungary). Natural and artificial leaves were exposed to separate the use of leaves as substrate and as food at different vertical positions. Although we recorded a low density of macroinvertebrates, mixed-effect models showed that natural leaves were colonized by a higher number of taxa and individuals than artificial leaves. Moreover, indicator species analysis identified two detritivorous species (Dikerogammarus villosus and Asellus aquaticus) as indicators of natural leaves. The obtained results suggest that macroinvertebrates use the leaves of reed not only as substrate but also as food. Leaf decay experiment showed that macroinvertebrates contribute to 87.5% of the total leaf litter decay. Leaf bags positioned at the surface were found to host less individuals but the decay rate was faster. The vertical position did not have an impact on the number of taxa or taxa composition. According to these results, macroinvertebrates represent an important component of detritus-based food webs in reed-vegetated littoral areas of the lake.