The loss of subsidies delivered by anadromous fish to inland stream ecosystems may have profound influences on stream food webs. However, studies have focused on food web responses in ecosystems where the fish assemblage is dominated by salmonids. We evaluated food web responses to carcass additions in three locations of an interior Columbia River Basin stream with varying native fish assemblages. Periphyton biomass responses were mixed with increases in treatment compared to control reaches of the middle and downstream pairs, but not in the upstream pair where scavenging by bears removed the majority of carcasses. Stable isotope analysis revealed marine-derived nutrient (MDN) enrichment of periphyton and invertebrate functional feeding groups in the middle and downstream pairs (up to 12% MDN derived), but not in the upstream pair. Non-salmonid fish exhibited limited MDN assimilation (~ 5 and 10% MDN derived), with isotopic enrichment patterns similar to lower trophic levels and little evidence of eggs and carcass material consumption, suggesting bottom-up transfer of MDN to non-salmonid fishes. In contrast, across the three study pairs, juvenile Chinook Salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss) assimilated MDN rapidly, obtaining up to 25% and 57% of their nitrogen from carcasses, respectively. Diet analysis and isotopic enrichment patterns indicated that juvenile salmonid assimilation occurred primarily through direct consumption of eggs and carcass tissue. Our findings suggest that salmonids in this region may experience more benefit from carcass additions containing eggs, while non-salmonids are likely to experience minimal MDN incorporation whether or not eggs are present.
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We thank C. Hayes, J. Dowdy, the ODFW Early Life History crew, and the Bureau of Reclamation summer interns for their assistance in field work. J. Dowdy, A. Dutterer, S. Favrot, W. Morton, A. Simpson, and staff of the Grande Ronde Model Watershed provided logistical assistance. B. Bilby, A. Kohler, and S. Collins provided feedback on initial experimental design. S. Johnson, W. Gerth, and I. Arismendi provided laboratory space and assistance. Ruth Bowman provided access to sites located on private property. This research was supported by the Bonneville Power Administration as part of the Columbia Basin Fish Accords Agreement (Project # 2009-004-00), an Oregon Watershed Enhancement Board (OWEB) Focused Investment Partnership (Project # 216-8205-15449), and a National Science Foundation Graduate Research Fellowship (Grant No. 1314109-DGE). The data that support the findings of this study are available from the corresponding author upon reasonable request.
MJK contributed to the study design, conducted research, analyzed data, and wrote the manuscript. SMW and DRW contributed to the study design, conducted research, and wrote the manuscript. ERS contributed to the study design and conducted research. AMS conducted research and wrote the manuscript.
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Kaylor, M.J., White, S.M., Sedell, E.R. et al. Carcass Additions Influence Food Webs Through Bottom-Up and Direct Consumption Pathways Along a Fish Species Assemblage Gradient. Ecosystems 24, 168–184 (2021). https://doi.org/10.1007/s10021-020-00510-x
- Food webs
- Salmon subsidies
- Columbia River Basin
- Stable isotopes
- Fish diets
- Marine-derived nutrients