Effects of spawning Atlantic salmon (Salmo salar) on total lipid content and fatty acid composition of river food webs

Abstract

Abstract. Returning Atlantic salmon subsidize rivers with marine-derived nutrients (MDNs), potentially altering food web dynamics, shifting to reliance on marine-derived resources. Stream channels designed to simulate natural river systems, one with MDNs from spawning Atlantic salmon (Salmo salar) and one without marine-nutrient subsidies (control), were used to determine whether fatty acids (FAs) delivered to rivers and streams by spawning Atlantic salmon are incorporated by freshwater biota. Changes in FA profiles between stream channels with and without MDN inputs for biofilm, macroinvertebrates, and Atlantic salmon parr were used to characterize temporal dynamics of MDN incorporation during pre-spawning, spawning, and post-spawning periods. There were no differences between control and treatment stream channels prior to the addition of Atlantic salmon. Spawning Atlantic salmon had a positive effect on total lipid content in all trophic levels (biofilm, 4.33%; macroinvertebrates, 7.54%; salmon parr, 2.59%), relative to controls. Fatty acid profiles between the MDN treatment and control stream channels were similar for each biotic group prior to the introduction of adult Atlantic salmon; however, following adult salmon introductions, the FA profiles of the biofilm, invertebrates, and salmon parr differed by as much as 36.7%, 30.3%, and 22.9%, respectively, between the MDN treatment stream channels and the controls. Fatty acid profiles of the invertebrates and salmon parr from the MDN treatment stream channels tracked the FA profile of the salmon eggs. Proportions of docosahexaenoic acid and eicosapentaenoic acid varied with diet in a predictable manner related to dietary FA proportions. These responses demonstrate a change in the food web structure resulting from the establishment of this new, marine-based, basal resource. The positive effects of MDNs increasing freshwater productivity are complimented by marine-based lipids that represent surplus energy and an increase in the quality of resources, thereby contributing to the diversity and health of freshwater ecosystems.

The diadromous watersheds-ocean continuum: Managing diadromous fish as a community for ecosystem resilience

“…Sea lamprey is hypothesized to condition habitats, making them more attractive and productive for salmon spawning (Saunders et al, 2006), although we do not have the empirical data to demonstrate this. Studies have shown that increased MDN benefits juvenile salmon growth (Guyette et al, 2013;Samways et al, 2017); however, we do not know whether these benefits result in increased survival and overall productivity. We also need to understand how diadromous fishes interact with other species, such as freshwater mussels, which are also at risk of extinction across most of their range and can improve fish habitat quality by biofiltration (Galbraith et al, 2018;Kreeger et al, 2018).…”

“…Northwestern Atlantic freshwater ecosystems are generally nutrient-poor, and there is relatively little information describing MDN dynamics for these systems. However, recent field studies have demonstrated that when rivers are enriched with MDN from diadromous fishes, the impacts include: changes in biofilm standing stock and productivity (Walters et al, 2009;Weaver et al, 2017), increased macroinvertebrates composition and abundance Samways et al, 2017;Weaver et al, 2018a), and increased juvenile fish growth (Guyette et al, 2013;Weaver et al, 2016Weaver et al, , 2018bSamways et al, 2017). MDN have also been shown to directly (consumption of diadromous fishes) and indirectly (consumption of prey that consumed diadromous fishes) benefit various avian species (Dalton et al, 2009;Call, 2015).…”

The effects of taxonomy, diet, and ecology on the microbiota of riverine macroinvertebrates

“…Bacterial communities in streams vary over time. Specifically, biofilms—which are collections of bacterial organisms that often adhere to surfaces such as rocks, small woody debris, and leaves—can differ in the abundances of Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria among seasons (Olapade & Leff, 2005); temporal differences in dissolved organic materials and inorganic nutrients likely drive differences among biofilms (Olapade & Leff, 2005; Samways et al., 2017, 2018). Temporal differences in alpha and beta diversity have also been found in free‐floating communities of bacterioplankton in freshwater streams that appeared to be driven by changes in stream water biogeochemistry (Portillo et al., 2012).…”

Atlantic salmon in regulated rivers: Understanding river management through the ecosystem services lens

“…Atlantic salmon are iteroparous, but between 20% and 100% of the adults nevertheless die after spawning (Nyqvist, 2016), and their carcasses may constitute a relevant nutrient addition for many rivers (McLennan et al, 2019). Moreover, during and after spawning, Atlantic salmon gametes are eaten by riverine organisms (Samways et al, 2017), also contributing to the linkage between the marine and freshwater ecosystems.…”