Stable isotope analysis of macroinvertebrates and their food sources in a glacier stream

Abstract

1. Food sources and trophic structure of the macroinvertebrate community along a longitudinal gradient were examined in a glacier stream of the Swiss Alps (Val Roseg). Analysis of multiple stable isotopes (δ13C and δ15N) and measurement of C : N ratios were used to differentiate between allochthonous and autochthonous organic matter. 2. Although isotopic signatures of algae varied widely among sites and dates, it was possible to discriminate between allochthonous and autochthonous food sources using a site‐specific approach. 3. Dominant food sources of herbivorous invertebrates in all main channel sites were epilithic diatoms and the filamentous gold alga Hydrurus foetidus. Allochthonous organic matter was of some importance only in a groundwater‐fed stream close to the floodplain margin. 4. Seasonal changes in the δ13C signature of the macroinvertebrates corresponded with seasonal changes in δ13C of the gold alga H. foetidus. This indicated that the energy base remains autochthonous throughout the year. 5. Because of limited food sources, feeding plasticity of the invertebrate community was high. Both grazers and shredders fed predominantly on algae, whereas gatherer‐collectors seemed to be omnivorous. 6. The overall enrichment of δ15N was 2.25‰ (r2=0.99) per trophic level. On a gradient from the glacier site to a downstream forested site trophic enrichment was constant but variation in δ15N within trophic levels decreased.

The distribution of littoral chironomids along an altitudinal gradient in High Tatra Mountain lakes: Could they be used as indicators of climate change?

“…However, identification of the trophic status of some species is often problematic due to considerable feeding mode flexibility and may lead to misinterpretations. Furthermore, Zah et al (2001) claimed that aquatic invertebrates are more plastic in utilizing food resources in extreme environmental conditions (e.g. alpine and arctic streams and lakes).…”

Trophic importance of benthic microalgae to macrozoobenthos in coastal bay systems in Korea: dual stable C and N isotope analyses

“…Indeed, seasonal changes in δ 13 C of primary producers are often rapidly reflected in the δ 13 C of invertebrates due to a high turnover rate for the assimilated carbon by the animals (Fry & Arnold 1982, Gleason 1986, Georing et al 1990, Riera & Richard 1997, Zah et al 2001. The rapidity of change and turnover of stable isotopes in animal tissues has been found even for fish and birds (Hobson & Clark 1992, Hesslein et al 1993.…”

Functional measures and food webs of high elevation springs in the Swiss alps

“…In the Alps, a large number of springs surface above treeline where the potential for autochthonous production is high (Zah et al, 2001;Füreder et al, 2003). Whether these ecosystems act as detritus-based systems as would be expected for springs below treeline is unknown (sensu Cross et al, 2003).…”

“…The grasses and herbs adjacent to alpine springs could be an important allochthonous source of organic matter and cause these systems to also rely strongly on detritus as a basal resource. In comparison, Zah et al (2001) found invertebrate herbivores in glacier streams above treeline to be reliant on autochthonous resources such as diatoms and the common gold alga Hydrurus foetidus, whereas allochthonous organic matter was an important basal resource in a nearby groundwater-fed stream (also see Füreder et al, 2003). Measures of ecosystem metabolism and stable isotope analysis of the food web would provide important information on the heterotrophic nature of alpine springs.…”