Effects of elevated CO₂ on speckled sanddab (Citharichthys stigmaeus) behaviour

The direct and indirect effects of ocean acidification (OA) are a growing concern, particularly in areas already experiencing elevated levels of oceanic CO₂. Studies with marine fishes suggest that elevated CO₂ levels may affect behavior by interfering with an important brain neurotransmitter. Studies examining the effects of OA fish behavior have been predominately conducted on tropical fishes; few have been conducted on fishes from temperate and boreal regions. The productive ecosystems of these regions, such as those of the California Current, support important commercial fisheries. Parts of the California Current are already experiencing elevated CO₂ during seasonal upwelling events. Flatfishes are an important component of the ecosystems of the California Current; not only do flatfishes support important regional fisheries, but they also are an important link in energy transfer within marine food webs. To date there has been little work examining the effects of OA on flatfish behavior. In laboratory experiments, I first examined speckled sanddab (Citharichthys stigmaeus) behavioral responses to potential predation cues (predator odor, damaged skin cues from injured conspecifics, and sight of a predator) under ambient CO₂ conditions. Whereas sanddab exhibited reductions in conspicuousness and foraging following exposure to the sight of a predator, they increased activity and foraging following exposure to damaged skin cues from injured conspecifics. I then examined the effects of elevated CO₂ levels on posture, activity, and foraging of sanddab, and if CO₂ altered their responses to damaged skin cues. CO₂ treatments reflected present-day CO₂ levels (~ 400μatm) and those predicted to occur over the next 150 years (~1,000 μatm and ~1,600 μatm). While there was no major effect of CO₂ treatment on the behavior of speckled sanddab, there were non-significant trends of fish from the medium CO₂ treatment exhibiting the lowest posture and activity scores, longest feeding latencies, and fewest feeding strikes. Results suggest that aspects of speckled sanddab behavior might resistant to OA. It is also possible that prolonged exposure to elevated CO₂ enabled speckled sanddab to compensate, mitigating the effects observed in other fishes following shorter-term exposure to elevated CO₂. Experiments further examining the interactive effects of elevated CO₂ with other environmental conditions on speckled sanddab behavior can also provide insight into the potential ecological consequences of life in an ocean altered by global climate change. Additional studies of ecologically relevant behaviors across diverse species assemblages will be needed to evaluate the impact of ocean acidification on marine food webs.

Andrade J. F., 2017. Effects of elevated CO₂ on speckled sanddab (Citharichthys stigmaeus) behaviour. MSc thesis, Oregon State University, 74 p. Thesis.

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