Annual migrations of anadromous salmon are an important source of nutrients for many coastal streams. Much of the current research on salmon-derived nutrients has focused on nutrient retention via carcass consumption by mammals, birds, and macroinvertebrates, whereas retention and transfer of nutrients by microbiota has received less attention. Our research objective was to investigate nutrient movement from decomposing salmon tissue into periphyton, bryophytes, leaf-pack microbiota, and amphipods in laboratory mesocosm streams. We measured δ¹⁵N of microbiota growing on unglazed tiles (periphyton), microbiota growing on leaf packs, bryophytes on partially submerged stones, and amphipods; C:N and C:P ratios of microbiota and bryophytes; and periphyton biomass (ash-free dry mass and chlorophyll a) in channels with and without decomposing salmon tissue. Periphyton, bryophytes, and leaf-pack microbiota had lower C:N ratios and leaf-pack microbiota had lower C:P ratios in salmon channels than in reference channels. These results indicate increased nutrient quality in salmon channels. Periphyton ash-free dry mass and chlorophyll a were greater in salmon channels than in reference channels. δ¹⁵N values for periphyton, leaf-pack microbiota, and bryophytes were more enriched in salmon channels than in reference channels, a result that demonstrates that salmon-derived nutrients can be retained in streams through multiple mechanisms. Transfer of salmon-derived nutrients through leaf-pack microbiota to a higher trophic level was evidenced by higher δ¹⁵N in amphipods from salmon channels than from reference channels. Last, higher P concentrations (as much as 90% higher) in biota from salmon channels than from reference channels indicate uptake of salmon-derived P in salmon channels. These results suggest that periphyton, leaf-pack microbiota, and bryophytes might play a critical role in capturing salmon-derived nutrients.