Ecological role of salmon on stream benthic macro-invertebrate populations in coastal ecosystems

Background/Question/Methods

Species that cross habitat boundaries can provide nutrient subsidies and engineer ecosystems through disturbance, which can alter local community structure.  Annual migrations of anadromous Pacific salmon (Oncorhynchus spp.) import marine-derived nutrients to oligotrophic freshwater streams but they can also disturb large portions of the stream bed when digging their nests.  The net effect of these two processes on stream consumers remains unclear.  Using mixed-effects modelling, we examined the dual role of spawning salmon on stream invertebrate community structure and diversity in the spring and fall, across a gradient of salmon density and habitat in coastal British Columbia, Canada.  

Results/Conclusions

Invertebrate density increased with stream temperature but decreased with salmon density and this was consistent for both spring and fall. In contrast, ∂₁₅N signatures in invertebrates increased with salmon density with elevated signatures in the fall compared to the spring.  Taken together, these results suggest that salmon-derived nutrients persist in these invertebrate communities months after salmon spawn; however this nutrient subsidy does not support higher invertebrate density.