Research article

Salmon-derived nitrogen in terrestrial invertebrates from coniferous forests of the Pacific Northwest

Morgan D Hocking and Thomas E Reimchen

Department of Biology, University of Victoria, PO Box 3020, Victoria, B.C. V8W 3NS, Canada

author email corresponding author email

BMC Ecology 2002, 2:4doi:10.1186/1472-6785-2-4

Published:	19 March 2002

Abstract

Background

Bi-directional flow of nutrients between marine and terrestrial ecosystems can provide essential resources that structure communities in transitional habitats. On the Pacific coast of North America, anadromous salmon (Oncorhynchus spp.) constitute a dominant nutrient subsidy to aquatic habitats and riparian vegetation, although the contribution to terrestrial habitats is not well established. We use a dual isotope approach of δ¹⁵N and δ¹³C to test for the contribution of salmon nutrients to multiple trophic levels of litter-based terrestrial invertebrates below and above waterfalls that act as a barrier to salmon migration on two watersheds in coastal British Columbia.

Results

Invertebrates varied predictably in δ¹⁵N with enrichment of 3–8‰ below the falls compared with above the falls in all trophic groups on both watersheds. We observed increasing δ¹⁵N levels in our invertebrate groups with increasing consumption of dietary protein. Invertebrates varied in δ¹³C but did not always vary predictably with trophic level or habitat. From 19.4 to 71.5% of invertebrate total nitrogen was originally derived from salmon depending on taxa, watershed, and degree of fractionation from the source.

Conclusions

Enrichment of δ¹⁵N in the invertebrate community below the falls in conjunction with the absence of δ¹³C enrichment suggests that enrichment in δ¹⁵N occurs primarily through salmon-derived nitrogen subsidies to litter, soil and vegetation N pools rather than from direct consumption of salmon tissue or salmon tissue consumers. Salmon nutrient subsidies to terrestrial habitats may result in shifts in invertebrate community structure, with subsequent implications for higher vertebrate consumers, particularly the passerines.