Stable isotope analysis of food webs in low Arctic lakes and streams and the structuring role of fish
MSc defence, Marie Buchardt
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AU-Silkeborg, Vejlsøvej 25, 8000 Silkeborg, D2.04
Little is known about Greenland freshwater food webs and how these are structured. It is known that fish can structure food webs by, for instance, performing top-down control. Fish have also been shown to couple different lake habitats due to their high mobility allowing them to feed in different habitats
Using stable isotope analysis, we investigated the structuring role of fish (particularly Arctic charr, Salvelinus alpinus, but also Gasterosteus aculeatus) in two fish-containing low Arctic lakes, deep Lake Badesø and shallow Lake Langesø, and 7 fishless and 7 fish-containing streams in the Kobbefjord area near Nuuk, Greenland. In addition, a stomach analysis was performed on Artic charr to verify the trophic position determined by the isotope analysis.
Isotope data revealed that Arctic charr occupied two trophic levels of the lake food webs and that it changes trophic position at a fork length of app. 20 cm. Arctic charr > 20 cm exploited the same carbon sources despite being caught in different habitats of the lake. The smaller Arctic charr (< 20 cm) fed on similar resources in shallow Langesø, but in the deeper Badesø there was a difference in food sources between lake zones. Use of Layman metrics on the isotope data from 14 streams, showed that the invertebrates in the fishless streams exploited a greater range of the food sources present and were more differentiated in their isotopic niche.
In conclusion, large Arctic charr were able to couple different lake habitats in the two investigated Greenland lakes, however smaller Arctic charr were only able to couple habitats in the shallow and smallest lake. In the streams, we also found that the presence of fish narrowed the invertebrate food webs due to top-down control, which led to a behavioural change of invertebrates to avoid predators.