The decomposition of organic matter (leaf litter) in streams and wetlands provides nutrients and energy for aquatic food webs, as well as for global carbon processing. Decomposition rates are influenced by abiotic factors as well as the feeding activity of shredding or grazing macroinvertebrates. Sunlight can stimulate algal growth in the biofilms that produce labile C and stimulate bacteria and fungi growth. Algae-rich biofilms may also be more nutritious for detritivores, affecting their feeding rates. This "priming effect" of algae in biofilms is hypothesized to influence the fate of organic C and nutrients in aquatic ecosystems. We imposed sun and shade treatments on leaf litter bags in a local waterbody to assess the effect of light on algal content of leaf biofilms, detritivore feeding activity and leaf decomposition rates. Coarse mesh litterbags (0.5 cm) filled with tulip poplar (Liriodendron tulipifera) leaves were immersed in floating plastic baskets underneath hardware cloth (high light), shade cloth (medium light) or solid plastic weed barrier fabric (heavy shade) for 8 weeks. Leaf discs (1.4 cm2) extracted in 90% acetone confirmed that biofilms of medium and heavily shaded litterbags contained less chlorophyll a than those exposed to sunlight. Early instar chironomid midges grew faster when fed leaf discs from sun-exposed litterbags than those from heavy shade. Their feeding activity accelerated leaf disc degradation in the lab but sun and shade treatments did not produce differences in decomposition in the field. More work is needed to better understand mechanisms of organic matter processing in heavily shaded, forest streams compared to open canopy stream-wetland complexes.