Application of liposome and stable isotope tracer techniques to study polyunsaturated fatty acid biosynthesis in marine zooplankton

We investigated the ability of four species of marine zooplankton to synthesize polyunsaturated fatty acids (PUFAs) during pulse-chase tracer experiments. Liposomes containing a deuterium labelled precursor fatty acid, D5-18:3n-3, were fed to female Calanus finmarchicus, Calanoides acutus, Drepanopus forcipatus and calyptopus larvae of Euphausia superba during ship-board experiments. Although all species of zooplankton readily ingested the liposomes and incorporated the D5-18:3n-3 tracer into their somatic lipid pool, only negligible products of elongation and desaturation; D5-18:4n-3, D5-20:5n-3 and D5-22:6n-3 were detected after 96 h incubations. We conclude that the four species of marine zooplankton examined here are unable to synthesize PUFA at ecologically significant rates and certainly not in amounts sufficient to support growth and reproductive processes.