The Ecology of Euphausiids using Lipid Biomarkers: Regional Comparisons

Abstract

Four species of euphausiids were collected from temperate (Northeast Pacific) and high-latitude (Antarctic) ocean to compare their ecology (i.e. feeding, reproduction) using lipid biomarkers. In the Northeast Pacific, Euphausia pacifica and Thysanoessa spinifera collected as part of the NEP GLOBEC program. In the Southern Ocean, Euphausia superba and E. crystallorophias, were collected in austral winter and fall as part fo the Southern GLOBEC program. For each collection, total lipid, lipid classes, and individual lipid biomarkers were examined in adults, juveniles and larvae. Antarctic krill were found to have much higher lipid content than their temperate relatives (10 ~ 50 and 5 ~ 20% of dry mass, respectively) with significant seasonal variations. Although the storage lipids (wax esters and triacylglycerols for E. crystallorophias and E. superba, respectively) were abundant in Antarctic species, phospholipids were the dominant lipid class in all species. Interestingly, phospholipids, generally known as structural lipids, were elevated with increasing total lipid content, suggesting as another energy reserves for over-wintering and reproduction in euphausiids. The fatty acids 16:0, 18:1(n-9), 20:5(n-3) were major components with minor differences between species and seasons in all species. 22:6(n-3) was absent from Antarctic species, but present in temperate species. Sterol profiles showed that cholesterol was the most abundant sterol in all krill species, with significant amounts of desmosterol found in Antarctic species and abundant in sea-ice algae. Based on lipid profiles, krill alter their diets with life stage and season. For instance, larvae of E. superba actively feed on sea-ice associated organisms while juveniles and adults feed on seston and copepods in the water column during austral winter. Individual lipid profiles suggest krill alter their diets dependent upon life stage and season. Particularly, larval stages not only occupy differe