Respiration rate and cost of swimming for Antarctic krill, Euphausia superba, in large groups in the laboratory

Constructing realistic energy budgets for Antarctic krill, Euphausia superba, is hampered by the lack of data on the metabolic costs associated with swimming. In this study respiration rates and pleopod beating rates were measured at six current speeds. Pleopod beating rates increased linearly with current speed, reaching a maximum of 6 beats s(-1) at 17 cm s(-1). There was a concomitant linear increase in respiration rate, from 1.8 mg O-2 g(D)(-1) h(-1) at 3 cm s(-1) to 8.0 mg O-2 g(D)(-1) h(-1) at 17 cm s(-1). The size of the group tested ( 50, 100 and 300 krill) did not have a significant effect on pleopod beating rates or oxygen consumption (ANCOVA, F= 0.264; P> 0.05). The cost of transport reached a maximum of 75 J g(-1) km(-1) at 5 cm s(-1), and then decreased with increasing current speed to 29 J g(-1) km(-1). When considered in light of energy budgets for E. superba, these data indicate that the cost of swimming could account for up to 73% of total daily metabolic expenditure during early summer.