Taxonomic composition and lake bathymetry influence fatty acid export via emergent insects

Abstract

1. The ecological role of emergent aquatic insects from lakes in exporting dietary polyunsaturated fatty acids (PUFA) across the freshwater-land interface is still poorly understood.<br /><br />2. In this field study, we explored the seasonal biomass export of emergent insects from three subalpine lakes and investigated how lipids of emergent insects were related to lake bathymetry, lipids of organic matter in lake sediments (i.e., basal resources), and the taxonomic composition of insects.<br /><br />3. The total lipid and PUFA fluxes of emergent insects were strongly related to taxonomy and lake bathymetry, but weakly associated with the PUFA content of the uppermost lake sediment layers. PUFA flux estimates of the dominant taxon, Chironomidae, from the shallowest lake (3 m depth; 125 g PUFA m⁻² season⁻¹) were considerably higher than those from the deepest lake (33 m depth; 56 g PUFA m⁻² season⁻¹), due to the higher per area biomass of emergent insects from this shallow lake. Insect taxonomy also affected the composition of PUFA transfer to land: Chironomidae were richer in ω-6 PUFA, such as linoleic acid (18:2n-6) and arachidonic acid (20:4n-6), whereas Ephemeroptera and Trichoptera contained more ω-3 PUFA, especially α-linolenic acid (18:3n-3) and eicosapentaenoic acid (20:5n-3).<br /><br />4. Our findings suggest that taxon-specific differences in PUFA content and lake bathymetry jointly shape PUFA fluxes and thus the provisioning of emergent insects as dietary sources of physiologically important PUFA for riparian consumers.