Towards an energy budget for krill: The physiology and biochemistry of Euphausia superba Dana

Published data on the oxygen consumption, nitrogen excretion, feeding, growth and moulting physiology of the Antarctic krill, Euphausia superba, are reviewed with particular reference to experimental methodology and the value of the data for the construction of an energy budget. It is concluded that the relationship between basal oxygen consumption (QO2, in ml h-1) and wet weight (W, in grams) can be described by the relationship QO2=0.0813 W0.88, that filtration rates in krill are high (but possibly reduced in dense swarms), and growth of adult krill in summer is about 2 mm per week. Using these data a preliminary energy budget has been constructed for adult krill at South Georgia in summer. This budget highlights the lack of data on the energetic costs of swimming and feeding in krill, and also the environmental and behavioural data necessary for the extrapolation of an individual energy budget to a swarm or whole population. This preliminary budget suggests a daily energy intake for male krill in summer of about 5% body weight per day. A minimal estimate of the cost of reproduction in female krill from the energy content of the ovary suggests that in a maturing female energy intake can be in excess of 6% body weight per day.