Experiments on the feeding of the Moon jellyfish Aurelia aurita have shown that digestion time of zooplankton typically varies between 2.2 and 5.1 h depending on the body weight of the predator, diet composition, amount of food, and seawater temperature. The daily ration of a Moon jellyfish with a wet body mass of 1 g reached 0.025-2.845 mg zooplankton.ind(-1).day(-1) corresponding to a carbon-specific food uptake of 0.2-9.1% C day(-1) with a mean value around 0.5% C day(-1). Such mesozooplankton consumption rates are consistent with the ration values (around 0.9% C day(-1)) calculated from the feeding rate experiments of jellyfish at natural food concentrations. However, in both cases the amount of mesozooplankton was insufficient to compensate for the minimum food requirements, calculated from oxygen consumption (6.7 +/- 0.6% C day(-1)) of the jellyfish. On average, the metabolic expenses of A. aurita were about one order of magnitude greater than its ration supplied by mesozooplankton, indicating the important role of visually overlooked food components in the jellyfish diet.