Multiple pathways of C and N incorporation by consumers across an experimental gradient of salmon carcasses

Abstract

Abstract. Numerous studies link resource subsidies to consumers, yet manipulations of subsidy gradients are rare, limiting our ability to predict their effects. We measured natural abundance levels of the stable isotopes of carbon (d 13 C) and nitrogen (d 15 N) in consumers representing two taxonomic (invertebrates, fish) and multiple trophic groups (primary, secondary, and tertiary consumers) exposed to a gradient of Pacific salmon carcasses (0-4 kg/m 2 , eight treatment levels) in 16 experimental streams from September to December. We hypothesized (1) that consumer among invertebrates. The only fish that responded positively to carcasses was a small benthic, secondary consumer, and only for d 13 C. Overall, benthic invertebrate primary consumers were the dominant pathway by which salmon organic matter entered the trophic system, followed by benthic secondary consumers, and then tertiary consumers (juvenile coho salmon and cutthroat trout) that occupy the water column. The attenuating response to subsidies at higher trophic levels was possibly due to a combination of low decomposition and metabolic rates during fall and winter, composition of the subsidy, and habitat use. Our results demonstrate that decomposing salmon carcasses provide variable but potentially important sources of C (range:~0-60%) and N (range:~0-35%) supporting benthic consumers during fall and winter, when environmental conditions constrain primary productivity, with some evidence of saturation at carcass loadings >0.1-0.6 kg/m 2 . Furthermore, stable isotope analysis showed that consumers exploited salmon organic matter in different ways, potentially alleviating competition and allowing for a more efficient processing of this resource subsidy.

Influence of riparian thinning on trophic pathways supporting stream food webs in forested watersheds

“…Wootton (2012) documented similar shifts in stream periphyton carbon signatures in response to canopy treatments of similar magnitude on the Olympic Peninsula in Washington, but this shift in carbon propagated up to the top consumer in the system-juvenile coho salmon. Kiffney et al (2018) observed responses similar to ours, where the experimental addition of salmon carcasses in western Washington streams shifted carbon and nitrogen isotope signatures of lower trophic levels, but not top predators. In contrast, McIntyre et al (2018) observed no change in stream periphyton stable isotope signatures or biomass in response to a range of riparian buffer treatments in Washington streams.…”

Colonization of a temperate river by mobile fish following habitat reconnection

“…Migratory anadromous Pacific salmon are considered strongly interacting species whose presence leads to significant ecological change, including altering species composition and energy flow (Kiffney et al, 2014;Lundberg & Moberg, 2003;Soulé et al, 2003). Although the number of adult coho salmon spawning above Landsburg Dam following restoration is relatively small compared with watersheds with healthy populations (Bradford et al, 1997(Bradford et al, , 2000Kiffney, Naman, et al, 2018;Moravek et al, 2021), we observed marked changes in the summer-time salmonid assemblage including a doubling in total biomass and increasing assemblage dissimilarity. These changes were primarily due to population-level changes in juvenile coho salmon and secondarily by mountain whitefish.…”

Anthropogenic Carrion Subsidy and Herbicide Glyphosate Depressed Leaf-Litter Breakdown: Effects on Environmental Health in Streams

“…The studies focused on the salmon carcasses have found that the input of carcasses can affect individuals and communities of macroinvertebrates and microbes (Chaloner et al, 2007;Verspoor et al, 2011). A considerable number of macroinvertebrates including caddisflies, mayflies, chironomids, and chloroperlids may benefit (e.g., increased growth rate and larger population biomass) from carrion subsidy via various pathways such as direct consumption of carrion tissue, grazing on microbes colonized on decaying carrion, shredding on enhanced quality of leaf-litter, feeding on small particle organic matter detached from decomposing carrion, and by preying on other invertebrates attracted by carrion (Minakawa et al, 2002;Fenoglio et al, 2005;Kiffney et al, 2018). Decaying carrion subsidy also provide nutrient-rich food resources for microbes including both fungi and bacteria, because macronutrients (e.g., N and P), micronutrients (e.g., Ca and K), fats, and proteins leached from carcasses can stimulate the growth of microbes (Wipfli et al, 1998;Fenoglio et al, 2010;Currier et al, 2020).…”