The chemical composition, metabolism, and feeding ecology of the cydippid ctenophore Callianira antarctica (Chun 1897) were investigated during autumn and winter 2001 and 2002 in the vicinity of Marguerite Bay, an embayment on the western Antarctic Peninsula shelf. C. an tarctica had relatively high carbon (C) and nitrogen (N) values (average: 8.4% C and 1.8% N [% dry weight, DW]), further suggesting that polar ctenophores are more C-rich than tropical species. Winter oxygen consumption and ammonium excretion rates ranged from 0.059 to 0.411 mu l O-2 mg(-1) DW h(-1) and 0.043 to 2.22 nmol N mg(-1) DW h(-1), respectively, at 0 degrees C. Calanoid copepods, larval and juvenile Antarctic krill Euphausia superba and a mixture of prey were offered to ctenophores during feeding incubations. Ingestion rates based on preliminary feeding experiments were linearly related to prey densities, with rates ranging from 9 to 39 prey ind.(-1) d(-1) and from 3.5 to 4.0 prey ind.(-1) d(-1) for 1 larger and I smaller C. antarctica, respectively. Daily rations varied between 22 and 136% of body C for the larger ctenophore and 6 to 22 % of body C for the smaller individual. Digestion time (median: 11.5 h) was dependent on prey elemental content and prey number, and was independent of ctenophore size. Gut content analyses indicated that C. antarctica preyed predominantly on larval euphausiids and copepods. Diver observations, net collections, and diet analyses suggest that this species is an opportunistic predator that feeds both during the day and night, and appears to be well adapted to the prey patchiness found in Antarctic waters.