Dosidicus gigas (d'Orbigny, 1835) is a large, active squid that undergoes a diel vertical migration in the Eastern Tropical and Temperate Pacific. It is a voracious predator on zooplankton and micronekton and supports a large fishery. It is further preyed upon by large vertebrate predators, including whales. Its horizontal distribution is closely tied to productive upwelling regions that are characterized by strong oxygen minimum zones (OMZs). The apparent association with extreme hypoxia is surprising given its large size and high oxygen demand. As part of its daily vertical migration, D. gigas experiences daily temperature changes of 15–20°C, oxygen partial pressures ranging from near anoxia (< 0.8 kPa) to air-saturation (21 kPa) and pH changes from ∼8.1 to < 7.6 at depth. Oxygen minimum zones are believed to be expanding due to climate change, with minimum oxygen levels in the core of the OMZ declining and the low oxygen horizon shoaling. Simultaneously, surface waters are becoming more acidic and temperatures are rising. Here I review the extensive studies of this species that have been conducted over the past decade. D. gigas has a high affinity respiratory protein in the blood that supports a low critical oxygen partial pressure (3.8 kPa at 20 °C) and aerobic survival at night in the upper 200 meters of the water column. A pronounced pH- and temperature sensitivity of oxygen binding promotes oxygen transport across a depth range and in support of high rates of oxygen utilization but may impose constraints on high-temperature and CO2 tolerance. At its deeper, colder daytime habitat depth, D. gigas undergoes a pronounced metabolic suppression. Reduced activity levels and an apparent suspension of transcription and translation contribute to a ∼80% reduction in oxygen demand under 1% oxygen (0.8 kPa at 10 °C). Anaerobic metabolic pathways contribute some energy under these conditions. This metabolic suppression likely limits feeding at depth. Sub-critical oxygen levels, rather than temperature, predator avoidance or prey availability, appear to set the daytime depth distribution. Thus, expanding oxygen minimum zones will alter the daytime depth of peak abundance for these squids while ocean acidification and warming may impose a shallow ceiling above which squid performance is limited. The role of climate change in setting the vertical and horizontal distribution of the species is discussed.
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Vol. 33 • No. 1