Metabolic suppression in thecosomatous pteropods as an effect of low temperature and hypoxia in the eastern tropical North Pacific

Many pteropod species in the eastern tropical North Pacific Ocean migrate vertically each day, transporting organic matter and respiratory carbon below the thermocline. These migrations take species into cold (15-10A degrees A C) hypoxic water (< 20 mu mol O-2 kg(-1)) at depth. We measured the vertical distribution, oxygen consumption and ammonia excretion for seven species of pteropod, some of which migrate and some which remain in oxygenated surface waters throughout the day. Within the upper 200 m of the water column, changes in water temperature result in a similar to 60-75 % reduction in respiration for most species. All three species tested under hypoxic conditions responded to low O-2 with an additional similar to 35-50 % reduction in respiratory rate. Combined, low temperature and hypoxia suppress the metabolic rate of pteropods by similar to 80-90 %. These results shed light on the ways in which expanding regions of hypoxia and surface ocean warming may impact pelagic ecology.