Depositional zones in headwater streams are colonized by a diverse community of benthic macroinvertebrates. These habitats have unique physical features that promote the emergence of a complex food wed. A strong seasonal variability was found for communities in the depositional zones of streams in the Montagne Noire region. The ecological functioning of these habitats was studied by focusing on litter breakdown and bioturbation. The intensity of these two processes is regulated by assemblages of specialized invertebrates : shredders and reworkers. We developed a method to quantify surface sediment reworking in order to assess this process in headwater streams. The capacity and mode of bioturbation differ substantially among stream reworkers. This work provides new empirical evidence on the biotic control of ecological functioning in streams.
