| Summary: | Increasing atmospheric CO₂ levels are causing a reduction of ocean surface water pH and shift in carbonate chemistry, a process termed ocean acidification. Ocean acidification poses a major threat to marine ecosystems, with a large body of work documenting negative effects of elevated CO₂ on a diverse range of shallow water coastal marine species. However, most studies to date have used stable CO₂ treatments, not considering the substantial diel CO₂ variation that occurs in many shallow water marine habitats. This thesis investigates how the presence of diel CO₂ cycles modifies the early development and behaviour of coral reef fishes under elevated CO₂, and how the effects of diel CO₂ cycles are further modified by elevated temperature and parental effects. In chapter 2 I investigate the interactive effects of elevated CO₂ and diel CO₂ cycles on juvenile survival, growth and otolith development in two species of coral reef fish. There was no effect of CO₂ treatment on survival and otolith development of Acanthochromis polyacanthus or Amphiprion percula. While growth was not significantly affected by CO₂ treatment in either species, there was a trend for fish reared under diel-cycling elevated CO₂ to be more similar in size to control fish, compared to those reared under stable elevated CO₂. These results suggest that the early development of juvenile coral reef fishes under future ocean acidification conditions is unlikely to be affected by diel cycles in CO₂. The behavioural alterations that have been observed in coral reef fishes under elevated CO₂ are likely to interact with diel CO₂ cycles, due to the concentration-dependent effects that stable elevated CO₂ has on onset times and the magnitude of behavioural impairments. Therefore, chapter 3 investigates the effects that diel CO₂ cycles have on behavioural lateralization in A. polyacanthus and response to a predator cue in Am. percula under elevated CO₂. As expected, exposure to stable elevated CO₂ caused behavioural impairments in both species. However, ...
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