Lipids as markers of nutritional condition and diet in the Antarctic krill Euphausia superba and Euphausia crystallorophias during austral winter
Se-Jong Ju and H. Rodger Harvey
To understand the nutritional condition and feeding history of Antarctic krill during winter, two species of krill, Euphausia superba and E. crystallorophias, were collected by MOCNESS during July-August 2001 in Marguerite Bay southeast of Adelaide Island. Total lipid, lipid classes, fatty acids, fatty alcohols and sterols were analyzed in animals among several life stages. Lipids in seston and major copepods collected from the water column and representing potential diets were also quantified and compared to krill. Stomach contents of adult krill were also examined in select animals to provide a visual snapshot of ingested material and allow comparison with lipid biomarkers. Total lipids in adult E. crystallorophias were significantly higher than adult E. superba (30.0 and 20.2% of dry weight, respectively). Wax esters were the major storage lipid in E. crystallorophias, accounting for over half (mean of 55.9%) of the total lipid in adult animals. In contrast, E. superba contained triacylglycerols as the dominant storage lipid in adults (mean of 45.5% of total lipid). Results for lipid classes and individual lipids suggest that E. superba is less dependent on stored lipid for overwintering than E. crystallorophias. Individual lipid profiles and stomach content of furcilia and adult E. superba find that animals vary their diets over time, with copepods representing a significant dietary source for adult animals in winter. Furciliae appears to feed largely on detritus and diatom dominated ice algae with lower levels of lipid storage.