Voyage of the argonauts in the pelagic realm: Physiological and behavioural ecology of the rare paper nautilus, Argonauta nouryi

Abstract

The metabolic demands of a rare paper nautilus, Argonauta nouryi, in the eastern tropical Pacific (ETP) are evaluated. After adjusting for temperature and size, the rates of oxygen consumption and of aerobic and anaerobic metabolic potential (as evidenced by citrate synthase and octopine dehydrogenase activities, respectively) of A. nouryi were much higher than those in holopelagic octopods that exhibit float-and-wait predation strategies. In fact, the rates were similar to those found in small epipelagic squids and benthic octopods. The critical oxygen partial pressure was 4.9 kPa at 20°C, suggesting that the strong oxygen minimum layer found at intermediate depths in the ETP may constrain the vertical distribution of A. nouryi to the upper few metres of the water column. We also report the occurrence of a chain of shelled females at the surface, in which each animal was attached, as if on the benthos, to the next individual in the chain. Although it may constitute an effective strategy to increase the rates of mate encounter in the vast open ocean, there may be an important ecological trade-off for such behaviour, namely the increase in visibility at the surface with concomitant attraction of predators. © 2010 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.