Trophic relations in a stream food web: importance of fatty acids for macroinvertebrate consumers

Abstract

Abstract Our study is a first attempt to characterize seasonal fatty acid (FA) profiles of foodweb components in a small forested stream. We measured FA content of autochthonous food sources (aquatic primary producers = periphyton, green algae, red algae, bryophytes), allochthonous food resources (terrestrial matter = benthic and transported organic matter [BOM and TOM, respectively]), and macroinvertebrate consumers (Hydropsyche spp., Ephemerella spp., isopods, oligochaetes). We examined whether FAs could be used as trophic markers and tried to identify which food sources best provided macroinvertebrates with essential FAs (EFA, ω3 and ω6 groups). Primary producers consistently had greater content of several EFAs (18:2ω6 and 18:3ω3 in green algae, 20:5ω3 in diatoms, 20:4ω6 in bryophytes) than did terrestrial matter. The ratio of Σω3/Σω6 FAs, a putative marker of the relative amount of autochthonous vs allochthonous matter, was greatest in macroinvertebrates, followed by algae, and was significantly corre...