Selective transfer of polyunsaturated fatty acids from phytoplankton to planktivorous fish in large boreal lakes.
Lake size influences various hydrological parameters, such as water retention time, circulation patterns and thermal stratification that can consequently affect the plankton community composition, benthic-pelagic coupling and the function of aquatic food webs. Although the socio-economical (particularly commercial fisheries) and ecological importance of large lakes has been widely acknowledged, little is known about the availability and trophic transfer of polyunsaturated fatty (PUFA) in large lakes. The objective of this study was to investigate trophic trajectories of PUFA in the pelagic food web (seston, zooplankton, and planktivorous fish) of six large boreal lakes in the Finnish Lake District. Docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and α-linolenic acid (ALA) were the most abundant PUFA in pelagic organisms, particularly in the zooplanktivorous fish. Our results show that PUFA from the n-3 family (PUFAn-3), often associated with marine food webs, are also abundant in large lakes. The proportion of DHA increased from ~4±3% in seston to ~32±6% in vendace (Coregonus albula) and smelt (Osmerus eperlanus), whereas ALA showed the opposite trophic transfer pattern with the highest values observed in seston (~11±2%) and the lowest in the opossum shrimp (Mysis relicta) and fish (~2±1%). The dominance of diatoms and cryptophytes at the base of the food web in the study lakes accounted for the high amount of PUFAn-3 in the planktonic consumers. Furthermore, the abundance of copepods in the large lakes explains the effective transfer of DHA to planktivorous fish. The plankton community composition in these lakes supports a fishery resource (vendace) that is very high nutritional quality (in terms of EPA and DHA contents) to humans.
Department of Biology, University of Eastern Finland, Box 111, FI-80101 Joensuu, Finland.
Ursula
U
Strandberg
Department of Biology, University of Eastern Finland, Box 111, FI-80101 Joensuu, Finland.
Minna
M
Hiltunen
Department of Biology, University of Eastern Finland, Box 111, FI-80101 Joensuu, Finland.
Elli
E
Jelkänen
Department of Biology, University of Eastern Finland, Box 111, FI-80101 Joensuu, Finland.
Sami J
SJ
Taipale
WasserCluster, Biological Station Lunz, Dr. Carl Kupelwieser Prom. 5, A-3293 Lunz am See, Austria.
Martin J
MJ
Kainz
Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195, USA.
Michael T
MT
Brett
Department of Biology, University of Eastern Finland, Box 111, FI-80101 Joensuu, Finland.
Paula
P
Kankaala
D000818:Animals; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D005399:Fishes / Q000378:metabolism*; D020387:Food Chain; D060106:Lakes; D010839:Phytoplankton / Q000378:metabolism*
D005231:Fatty Acids, Unsaturated
Boreal lake; Cladocerans; Copepods; Coregonus albula; Osmerus eperlanus; Phytoplankton; Planktivorous fish; Zooplankton