| Dosidicus gigas is a large, epipelagic squid known to vertically migrate, spending night on the surface, and descending during the day into the oxygen minimum layer (OML). This dissertation seeks to examine physiological and behavioral adaptations of D. gigas to the environment in which it dwells.;Life in the open ocean is unique in that there is little physical refuge. In order to capture prey in this environment, many pelagic fishes engage at high relative swimming speeds attempting to strike before being detected. This requires high metabolic rates and increasing anaerobic potential with increasing body size to overcome drag. I hypothesized that the activity of anaerobically poised enzymes would be high and increase with size. In contrast, I demonstrate that anaerobic metabolic capacity in D. gigas is lower than high performance fishes and scales negatively with body mass.;I developed a novel ship-board swim tunnel respirometer to measure aerobic metabolic rates in conditions of the OML and surface waters. I found that D. gigas has one of the highest aerobic metabolic rates of any organism in the ocean. There was a marked decrease of metabolism with decreased temperature, but oxygen consumption still out paced available environmental oxygen. The critical partial pressure was similar to other cephalopods from the OML, but higher than the oxygen partial pressure in the OML. I observed that D. gigas was able to survive prolonged periods of anoxia (1-2 h) in a lethargic state. Our data suggests that D. gigas survives in the OML by suppressing metabolism. Preliminary cost of transport (COT) values were high, which is likely drives the high routine aerobic metabolic rate observed.;Cephalopods have the ability to rapidly alter their external appearance by using chromatophores and body postures. Work describing these behaviors has focused on shallow, nearshore species dwelling in complex environments. This has led to the hypothesis that species from less complex environments will have a limited body pattern repertoire. Here I test this hypothesis by creating an ethogram for D. gigas, a cephalopod from a simple environment. I found this species has a catalog of components comparable in diversity, if not complexity, to cephalopods from the nearshore. |
