title: Distinctive lipid composition of the copepod Limnocalanus macrurus with a high abundance of polyunsaturated fatty acids.
abstract: We studied the copepod Limnocalanus macrurus for seasonal variation in the composition of fatty acids, wax esters and sterols in large boreal lakes, where it occurs as a glacial-relict. Vast wax ester reserves of Limnocalanus were accumulated in a period of only two months, and comprised mono- and polyunsaturated fatty acids (PUFA) and saturated fatty alcohols. In winter, the mobilization of wax esters was selective, and the proportion of long-chain polyunsaturated wax esters declined first. PUFA accounted for >50% of all fatty acids throughout the year reaching up to ca. 65% during late summer and fall. Long-chain PUFA 20:5n-3 and 22:6n-3 together comprised 17-40% of all fatty acids. The rarely reported C24 and C26 very-long-chain PUFA (VLC-PUFA) comprised 6.2 ± 3.4 % of all fatty acids in August and 2.1 ± 1.7% in September. The VLC-PUFA are presumably synthesized by Limnocalanus from shorter chain-length precursors because they were not found in the potential food sources. We hypothesize that these VLC-PUFA help Limnocalanus to maximize lipid reserves when food is abundant. Sterol content of Limnocalanus, consisting ca. 90% of cholesterol, did not show great seasonal variation. As a lipid-rich copepod with high abundance of PUFA, Limnocalanus is excellent quality food for fish. The VLC-PUFA were also detected in planktivorous fish, suggesting that these compounds can be used as a trophic marker indicating feeding on Limnocalanus.
authors.affiliation: Department of Biology, University of Eastern Finland, P.O. Box 111, 80101, Joensuu, Finland, minna.hiltunen@uef.fi.
authors.forename: Minna
authors.initials: M
authors.lastname: Hiltunen
authors.forename: Ursula
authors.initials: U
authors.lastname: Strandberg
authors.forename: Markku
authors.initials: M
authors.lastname: Keinänen
authors.forename: Sami
authors.initials: S
authors.lastname: Taipale
authors.forename: Paula
authors.initials: P
authors.lastname: Kankaala
mesh_terms: D000818:Animals; D002849:Chromatography, Gas; D033342:Copepoda / Q000737:chemistry* / Q000378:metabolism*; D017753:Ecosystem; D004952:Esters / Q000032:analysis; D005227:Fatty Acids / Q000032:analysis / Q000737:chemistry; D005231:Fatty Acids, Unsaturated / Q000032:analysis*; D005387:Finland; D060106:Lakes; D008055:Lipids / Q000032:analysis* / Q000737:chemistry*; D012621:Seasons; D013261:Sterols / Q000032:analysis; D015048:Zooplankton
chemical_list: D004952:Esters; D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D008055:Lipids; D013261:Sterols
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