Abstract
As atmospheric CO2 levels rise, the CO2 concentration in ocean surface waters increases through a process commonly referred to as ocean acidification. Recently, surprising behavioural modifications has been detected in the early life stages of tropical coral reef fish exposed to ocean acidification-relevant CO2 concentrations, but it has been unclear if this effect could occur in temperate waters. Here we show several severe behavioural disturbances, including effects on boldness, exploratory behaviour, lateralisation, and learning in a temperate fish, the three-spined stickleback (Gasterosteus aculeatus). The behavioural effects were consistent throughout the exposure period and increased in effect size with exposure time. We observed the effects on adult sticklebacks, a species known to be tolerant to other environmental stressors. Our findings suggest that behavioural abnormalities that stem from CO2 exposure are not restricted to sensitive tropical species or early life stages and may therefore affect fish on a global scale. The severity of disturbances and the possibility of a serious behavioural problem for fish across the globe is cause for concern.
Highlights
Anthropogenic CO2 emissions are increasing the atmospheric CO2 concentration, which drives increasing dissolution of CO2 into the oceans through a process commonly referred to as ocean acidification [1]
The control fish showed a wide spread of turning preferences, shown as relative lateralization index, while the CO2-exposed fish had a reduced distribution
This difference is shown as absolute lateralization index (Figure 4) where the average turning preference is reduced by CO2-exposure
Summary
Anthropogenic CO2 emissions are increasing the atmospheric CO2 concentration, which drives increasing dissolution of CO2 into the oceans through a process commonly referred to as ocean acidification [1]. As fish are active organisms with a high metabolism, their muscle activity produces CO2 at a variable rate. They experience internal fluctuations in CO2 concentration. The gill is the major organ for pH regulation where hydrogen ions are excreted and bicarbonate ions absorbed [2]. These mechanisms effectively buffer the blood pH during transient periods of high water CO2 concentration, and fish have been assumed to be tolerant to the relatively modest CO2-challenge of ocean acidification [3,5]. Maintaining blood pH despite CO2 exposure, requires modifications in concentrations of blood ions, including increased HCO32, decreased Cl2, and increased Na+ concentrations [5,6,7]
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