Do invertebrates matter? Detrital processing in the River Swale–Ouse

A litter bag experiment was used to examine the role of macroinvertebrate communities in the processing of terrestrially derived (allochthonous) organic material at headwater, mid-reach and lower reach sites on the River Swale–Ouse system, North Yorkshire, UK. Data from the study indicates that the role of macroinvertebrates in leaf litter processing within the River Swale–Ouse system is minimal, and not measurable by the technique used. Thus it is unlikely that in this river system macroinvertebrates have a significant effect on either the size of the resident detrital pool or the rate of production of fine particulate organic matter. Highest numbers of both total invertebrates and shredder species were recorded in bags at the mid-reach site. This pattern conflicts with the river continuum concept model which presumes the greatest abundance and role of shredder invertebrates in headwater streams.