Lipid turnover reflects life-cycle strategies of small-sized Arctic copepods

Abstract

This study aimed at understanding how life-cycle strategies of the primarily herbivorous Pseudocalanus minutus and the omnivorous Oithona similis are reflected by their lipid carbon turnover capacities. The copepods were collected in Billefjorden, Svalbard, and fed with 13C labeled flagellates and diatoms during 3 weeks. Fatty acid (FA) and fatty alcohol compositions were determined by gas chromatography, 13C incorporation was monitored using isotope ratio mass spectrometry. Maximum lipid turnover occurred in P. minutus, which exchanged 54.4% of total lipid, whereas 9.4% were exchanged in O. similis. In P. minutus, the diatom markers 16:1(n-7), 16:2(n-4) and 16:3(n-4) were almost completely renewed from the diet within 21 days, while 15% of the flagellate markers 18:2(n-6), 18:3(n-3) and 18:4(n-3) were exchanged. In O. similis, 15% of both flagellate and diatom markers were renewed. P. minutus exhibited typical physiological adaptations of herbivorous copepod species, with a very high lipid turnover rate and the ability to integrate FAs more rapidly from diatoms than from flagellates. O. similis depended much less on lipid reserves and had a lower lipid turnover rate, but was able to ingest and/or assimilate lipids with the same intensity from various food sources, to sustain shorter periods of food shortage.