Cross-ecosystem fluxes: Export of polyunsaturated fatty acids from aquatic to terrestrial ecosystems via emerging insects.
Cross-ecosystem fluxes can crucially influence the productivity of adjacent habitats. Emerging aquatic insects represent one important pathway through which freshwater-derived organic matter can enter terrestrial food webs. Aquatic insects may be of superior food quality for terrestrial consumers because they contain high concentrations of essential polyunsaturated fatty acids (PUFA). We quantified the export of PUFA via emerging insects from a midsize, mesotrophic lake. Insects were collected using emergence traps installed above different water depths and subjected to fatty acid analyses. Insect emergence from different depth zones and seasonal mean fatty acid concentrations in different insect groups were used to estimate PUFA fluxes. In total, 80.5mg PUFA m-2yr-1were exported, of which 32.8mgm-2yr-1were eicosapentaenoic acid (EPA), 7.8mgm-2yr-1were arachidonic acid (ARA), and 2.6mgm-2yr-1were docosahexaenoic acid (DHA). While Chironomidae contributed most to insect biomass and total PUFA export, Chaoborus flavicans contributed most to the export of EPA, ARA, and especially DHA. The export of total insect biomass from one square meter declined with depth and the timing at which 50% of total insect biomass emerged was correlated with the water depths over which the traps were installed, suggesting that insect-mediated PUFA fluxes are strongly affected by lake morphometry. Applying a conceptual model developed to assess insect deposition rates on land to our insect-mediated PUFA export data revealed an average total PUFA deposition rate of 150mgm-2yr-1within 100m inland from the shore. We propose that PUFA export can be reliably estimated using taxon-specific information on emergent insect biomass and seasonal mean body PUFA concentrations of adult insects provided here. Our data indicate that insect-mediated PUFA fluxes from lakes are substantial, implying that freshwater-derived PUFA can crucially influence food web processes in adjacent terrestrial habitats.
Limnological Institute, University of Konstanz, Mainaustrasse 252, 78464 Konstanz, Germany. Electronic address: Dominik.Martin-Creuzburg@uni-konstanz.de.
Dominik
D
Martin-Creuzburg
Limnological Institute, University of Konstanz, Mainaustrasse 252, 78464 Konstanz, Germany. Electronic address: Carmen.Kowarik@uni-konstanz.de.
Carmen
C
Kowarik
Limnological Institute, University of Konstanz, Mainaustrasse 252, 78464 Konstanz, Germany. Electronic address: Dietmar.Straile@uni-konstanz.de.
Dietmar
D
Straile
D000818:Animals; D017753:Ecosystem; D005231:Fatty Acids, Unsaturated / Q000032:analysis*; D020387:Food Chain; D007313:Insecta; D060106:Lakes; D012621:Seasons
D005231:Fatty Acids, Unsaturated
Aquatic-terrestrial coupling; Chaoborus; Chironomidae; Docosahexaenoic acid; Eicosapentaenoic acid; Insect emergence; Resource subsidies