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.

Keywords

• anadromous fish
• Atlantic salmon
• biofilm
• Eastern Canada
• fatty acids
• food web dynamics