• aquatic macrophyte;
  • ecological stoichiometry;
  • organic carbon;
  • shredder;
  • stable isotope

Abstract  Human induced alterations to rivers and steams have resulted in significant changes to the structure and diversity of riparian and aquatic plant communities. These changes will impact on the dynamics of riverine carbon cycles and food web structure and function. Here we investigate the principal sources of organic carbon supporting local shredder communities across a gradient in different levels of anthropogenic development along riverine reaches, in South Australia. In forested/wooded reaches with minimum to limited development, semi-emergent macrophytes were the principal sources of organic carbon supporting the local shredder communities. However, in developed reaches, course particulate organic matter and filamentous algae were the principal food sources. The C:N ratios of the food sources in developed reaches were higher than those of their consumers indicating a stoichiometric mismatch. This imbalanced consumer-resource nutrient ratio in those developed reaches is likely to impose constraints on the growth and reproduction of their aquatic shredder communities with probable knock-on effects to higher trophic levels.