| Summary: | Oceanic uptake of anthropogenic carbon dioxide (CO₂) is causing changes to seawater chemistry, a process known as ocean acidification. This has the potential to negatively affect a wide variety of marine organisms. To date, most studies into the effects of elevated CO₂ on marine organisms have focused on highly calcified invertebrates and fishes, with a variety of effects observed, including impacts on early life history development, respiration, behaviour, and learning. Despite their importance in marine ecosystems, comparatively little is known about the possible effects of rising CO₂ levels on cephalopods. In this thesis, I investigate the effects of CO₂ levels projected for the end of this century on the aerobic scope, reproduction, development, predatory behaviours, and learning in two species of tropical cephalopod from different taxonomic orders, the two-toned pygmy squid (Idiosepius pygmaeus) and the bigfin reef squid (Sepioteuthis lessoniana). In Chapter 2, I investigate the effects of elevated CO₂ on the minimum and maximum oxygen uptake rates, and aerobic scope of both I. pygmaeus and S. lessoniana. Due to the pH sensitive oxygen transport of cephalopods, I expected adverse effects on oxygen uptake rates. However, there were no effects of elevated CO₂ exposure on oxygen uptake rates or aerobic scope. This suggests a level of tolerance to elevated CO₂ in both species. The ability of these two cephalopod species to cope with long-term exposure to elevated CO₂ without detriment to their aerobic scope suggests that the energy available to partition to other important tasks, such as reproduction and growth, may remain optimal at elevated CO₂. One of the more commonly observed effects of elevated CO₂ on marine molluscs is altered reproduction and early life history development. In Chapter 3, I test the effects of elevated CO₂ on reproduction and the potential for effects after parental exposure on early development in I. pygmaeus. Despite the lack of effects of elevated CO₂ on the aerobic scope of adults ...
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