| Summary: | The amount of carbon dioxide dissolved in the oceans is steadily rising due to a 40% increase in atmospheric CO₂ since the industrial revolution, leading to significant changes in water chemistry. Recent studies show that larval reef fish exposed to near future concentrations of CO₂ experience impaired ability to discriminate between olfactory cues and exhibit changes in behaviour that increase post-settlement mortality. Reef fishes at all life history stages rely on olfactory cues for critical behaviours including feeding, reproduction, predator avoidance, and the establishment and maintenance of habitat associations. However, it is unknown if olfactory impairment due to elevated CO₂ observed in larval fish will affect critical ecological processes, such as habitat selection at settlement, and if sensory disruption will also occur in adults. This thesis examines the effects that CO₂ concentrations predicted to occur in the ocean this century (550-950ppm) have on habitat associations of coral reef fishes. Fishes tested in each study were selected to assess behavioural responses to high-CO₂ conditions at both larval and adult stages and across multiple reef fish taxa, using species with varying degrees of habitat specialisation and habitat use. The chapters comprising this thesis address the following questions: 1) does olfactory impairment alter habitat selections and settlement behaviour of larval reef fishes when all sensory cues are available?; 2) does elevated CO₂ cause sensory impairment in adult fish, and if so how might olfactory-mediated processes such as homing behaviour be affected?; and 3) does elevated CO₂ affect habitat preferences of habitat specialist species? As larvae of many reef fish species settle to benthic substrates overnight and during new moon phases, when low light aids in predator avoidance, olfaction is potentially the key sensory system employed during the settlement process. The effect of elevated CO₂ on larval behaviour and habitat preferences was tested in three species of ...
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