Abstract
AbstractTrophic transfer and retention of dietary compounds are vital for somatic development, reproduction, and survival of aquatic consumers. In this field study, stable carbon and nitrogen isotopes, and fatty acids (FA) contents in invertebrates and fishes of pre‐alpine Lake Lunz, Austria, were used to (1) identify the resource use and trophic level of Arctic charr (Salvelinus alpinus), pike (Esox lucius), perch (Perca fluviatilis), brown trout (Salmo trutta), roach (Rutilus rutilus), and minnow (Phoxinus phoxinus) and (2) examine how polyunsaturated fatty acids (PUFA; i.e., omega‐3 and ‐6PUFA) are related to total lipid status, littoral–pelagic reliance, and trophic position. Stable isotope data suggest that pike, perch, and minnow derived most of their energy from littoral resources, but minnows differed from pike and perch in their trophic position andPUFAcomposition. The co‐occurrence of cyprinids, percids, and pike segregated these fishes into more lipid‐rich (roach, minnow) and lipid‐poor (pike, percids) species. Although the relatively lipid‐poor pike and percids occupied a higher trophic position than cyprinids, there was a concurrent, total lipid‐dependent decline in omega‐3 and ‐6PUFAin these predatory fishes. Results of this lake food‐web study demonstrated that total lipids in fish community, littoral–pelagic reliance, and trophic position explained omega‐3 and ‐6PUFAin dorsal muscle tissues. Omega‐3 and ‐6PUFAin these fishes decreased with increasing trophic position, demonstrating that these essential FAs did not biomagnify with increasing trophic level. Finally, this lake food‐web study provides evidence of fish community‐level relationship between total lipid status andPUFAor stable isotope ratios, whereas the strength of such relationships was less strong at the species level.
Highlights
Essential dietary nutrients, including omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFA), must be supplied to consumers to support their somatic growth, reproduction, and survival (Parrish 2009)
Results of this lake food-web study demonstrate that total lipids in fish, independent of their taxa, littoral–pelagic reliance, or trophic level, predicted the n-3 and n-6 PUFA mass fractions in their dorsal muscle tissues and confirm our alternative hypothesis that fishes adjust their PUFA according to their total lipid status
N-3 and n-6 PUFA in these freshwater fishes decrease with increasing trophic position, implying that these essential FA do not accumulate with increasing trophic level
Summary
Essential dietary nutrients, including omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFA), must be supplied to consumers to support their somatic growth, reproduction, and survival (Parrish 2009). Understanding trophic dynamics of such essential dietary nutrients in aquatic food webs is an essential component of community ecology. In the pelagic component of the food web, phytoplankton are the key resource for zooplankton that are foraged on by planktivorous fishes and piscivores. Many fish species obtain their dietary energy from one particular diet source, but via highly dynamic feeding strategies and the use of multiple feeding grounds (“linked food chains”; Post et al 2000; e.g., Schindler and Scheuerell 2002, Vander Zanden and Vadeboncoeur 2002, Hayden et al 2014a). Vander Zanden et al (2006) investigated lake trophic dynamics in a subalpine lake and showed that fish retrieved their dietary energy from both benthic and pelagic habitats, but demonstrated that fish production was circa five times more supported by benthic than by pelagic resources. The recognition of different energy pathways to lake fishes has important implication for assessing the availability and retention of dietary energy and its nutritional quality
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