Effects of nutrient subsidies on trophic and population ecology of resident fish

Background/Question/Methods

The movements of organisms and nutrients across ecosystem boundaries can greatly affect the composition and dynamics of food webs. A pertinent example of these processes for coastal areas of the North Pacific is the linkage of marine and aquatic ecosystems through massive transfers of nutrient subsidies to freshwaters by annual spawning runs of Pacific salmon (Oncorhynchus spp.). Though this process has been well recognized, effects of these nutrient subsidies on dynamics of recipient foodwebs and consumer populations remain poorly understood. Key consumers in such recipient systems are freshwater sculpins (Cottus spp.), which are often the most abundant fish in coastal freshwaters. We use stable isotope analysis and population surveys in coastal watersheds on the Central Coast of British Columbia, Canada to determine how nutrients from salmon affect the trophic ecology of sculpins, and how this in turn scales up to population level impacts.  

Results/Conclusions

We show that both salmon-derived nutrients in sculpin diets and sculpin population densities are positively correlated with increasing availability of this resource across a gradient of salmon spawning densities. Our results also indicate that season, sculpin size, species, and physical habitat characteristics play roles in dictating the strength of these relationships.