Seasonal variation in body composition, metabolic activity, feeding, and growth of adult krill Euphausia superba in the Lazarev Sea

We investigated physiological parameters (elemental and biochemical composition, metabolic rates, feeding activity and growth) of adult Antarctic krill in the Lazarev Sea in late spring (December), mid autumn (April) and mid winter (July and August) to evaluate proposed hypotheses of overwintering mechanisms. Our major observations are: (1) respiration rates were reduced by 30 to 50% in autumn and winter, compared to values in late spring; (2) feeding activity was reduced by 80 to 86% in autumn and winter, compared to late spring, at similar food concentrations; (3) feeding was omnivorous during winter; (4) with each moult, krill grew by 0.5 to 3.8% in length; (5) body lipids and, to a small extent, body proteins were consumed during winter. Adult Euphausia superba thus adopt metabolic slowdown and omnivorous feeding activity at low rates to survive the winter season in the Lazarev Sea. By mid autumn, metabolic activity is reduced, most likely being influenced by the Antarctic light regime, which is accompanied by a reduction in feeding activity and growth. Although at a low level, the feeding activity during winter seems to provide an important energy input.