Fatty acid composition as an indicator of carnivory in Antarctic krill, Euphausia superba

In a previous study at South Georgia, carnivory was invoked as a cause of high polyunsaturated fatty acid (PUFA) content of Antarctic krill, Euphausia superba. To examine this, krill were sampled and fed for 16 days exclusively on the locally abundant copepod Drepanopus forcipatus. After 16 days, the krill had increased their PUFA content from 28 to 54% of the total fatty acids. Concurrently, monounsaturated fatty acids (MUFAs) and saturated fatty acids (SFAs) decreased from 41 to 27%. Thus, the krill appeared to accumulate PUFAs as reflected in their diet of D. forcipatus, which also had a relatively high PUFA content (50%). Overall, the results support omnivorous feeding by krill at South Georgia during nonbloom periods. We propose that the ratio of PUFA to SFA content may be used to detect carnivory in the recent feeding history of krill and suggest that this may be an index which could be applied to other zooplankton.