Supplementary material from "Will giant polar amphipods be first to fare badly in an oxygen-poor ocean? Testing hypotheses linking oxygen to body size"

It has been suggested that giant Antarctic marine invertebrates will be particularly vulnerable to declining O₂ levels as our ocean warms in line with current climate change predictions. Our study provides some support for this Oxygen Limitation Hypothesis with larger body sizes being generally more sensitive to O₂ reductions than smaller body sizes. However, it also suggests that the overall picture is a little more complex. We tested predictions from three different, but overlapping, O₂-related hypotheses accounting for gigantism, using four, Antarctic amphipod species encompassing a wide range of body sizes. We found a significant effect of body size, but also of species, in their respiratory responses to acutely declining O₂ tensions. The more active lifestyle of intermediate-sized Prostebbingia brevicornis was supported by a better respiratory performance than predicted by the Oxygen Limitation Hypothesis alone, but consistent with the Symmorphosis Hypothesis. We suggest that giant polar amphipods are likely to be some of the first to fare badly in an O₂-poor ocean. However, the products of past evolutionary innovation, such as respiratory pigments that enhance O₂-transport and novel gas exchange structures, in some species, may offset any respiratory disadvantages of either large or small body size.This article is part of the theme issue ‘Physiological diversity and global patterns of biodiversity in a time of global climate change: testing and generating key hypotheses involving temperature and oxygen’.