Metabolic rates and elemental and biochemical composition of Furcilia IV (FIV) larvae of Euphausia superba were studied during 12 d of starvation at the onset of winter in the Bellingshausen Sea. This time of the year may be a critical period in the krill life cycle because their larvae must switch from feeding on summer phytoplankton blooms to winter ice algae. FIV utilized mainly lipids overall, but also protein during the second half of the 12 d period. After 6 d of starvation most of the larvae lost half of their body C. Body lipid content decreased from 12.7 to 1.5% of dry mass (DM), whereas protein fell from 32.7 to 25.8% of DM. Respiration rates decreased from 1.3 to 0.7-0.8 μl O2 (mg DM)-1 h-1 in the first 3 d, after which they remained roughly constant. These rates correspond to C losses of 2.7 and 2.0% body C d-1 respectively. Excretion rates decreased from 0.04 to 0.02 μg NH4 (mg DM)-1 h-1 until the middle of the starvation period and then rose to 0.05 μg NH4 (mg DM) -1 h-1 by the end, which is probably related to the increase in protein breakdown. Based on these losses of body C and lipid, the FIV larvae may pass their point of no return, where they lose their ability to recover from nutritional stress, after 6 d. © Inter-Research 2005.