Life history of Gonatus onyx (Cephalopoda : Teuthoidea): ontogenetic changes in habitat, behavior and physiology

In the present study 670 individuals of Gonatus onyx (Cephalopoda: Teuthoid ea) were observed in Monterey Bay, California from a remotely operated vehi cle. The vertical distribution of this species was bimodal, with peaks at 4 00 and 800 m depth during the day and 300 and 500 m during the night. The b imodal distribution reflects a life stage shift between younger, schooling juveniles living in shallower water and older, solitary adults which live d eeper. Ontogenetic changes in behavior associated with this life stage shif t are reflected in the physiology of the organisms as well. Both aerobic an d anaerobic metabolism, as estimated using mitochondrial and glycolytic enz ymes, decline with increasing body mass, suggesting reduced locomotory capa city in deeper-living adults. Oxygen consumption rates were also determined in relation to oxygen partial pressure. Oxygen consumption regulation was similar between juvenile and adult squids. The critical oxygen partial pres sures (29 to 30 mmHg) correspond precisely to the oxygen concentrations fou nd at the depth of maximal abundance for day and night populations of juven iles and adults, respectively. Behavioral and physiological changes with on togeny of G. onyx are believed to result from reduced visual predator/prey interactions in the light-limited deep sea.