SPEED, JET PRESSURE AND OXYGEN CONSUMPTION RELATIONSHIPS IN FREE-SWIMMING NAUTILUS

ducers were attached to Nautilus pompilius L. to record mantle cavity pressures while the animals were induced to swim in a flume in response to food. 2. Synchronized videotapes and computer data files showed that jet pressures (p, Pa) increased linearly with swimming speed (M, ms"1), p=1565u-8. 3. Because of their stereotyped responses to food, Nautilus could be induced to produce similar pressures in 51 respirometers, where oxygen consumption (VOv ml kg"1) increased as a power function of pressure, KO2=3.85/?0'584. 4. Combining these equations gave an oxygen consumption-speed relation-ship, VO2=283H0'5 8 4. We used this equation to show that the cost of transport for Nautilus is dramatically lower than that for squid and, at speeds below 0.05 m s"1, even lower than that of an undulatory swimmer, the salmon. 5. Calculated power inputs and outputs suggest that squid have increased their power density (\Vkg~1) 100-fold over their ectocochleate ancestors, and that Nautilus is very efficient in its low-speed, low-energy environment. 6. These laboratory 'calibrations ' are a basis for field studies using telemetered pressure data to develop energy budgets for this unique living fossil as a reference for comparing the energetic requirements of ancient and modern seas