Effects of ocean acidification on visual risk assessment in coral reef fishes

1. With the global increase in CO2 emissions, there is a pressing need for studies aimed at understanding the effects of ocean acidification on marine ecosystems. Several studies have reported that exposure to CO2 impairs chemosensory responses of juvenile coral reef fishes to predators. Moreover, one recent study pointed to impaired responses of reef fish to auditory cues that indicate risky locations. These studies suggest that altered behaviour following exposure to elevated CO2 is caused by a systemic effect at the neural level.
2. The goal of our experiment was to test whether juvenile damselfish Pomacentrus amboinensis exposed to different levels of CO2 would respond differently to a potential threat, the sight of a large novel coral reef fish, a spiny chromis, Acanthochromis polyancanthus, placed in a watertight bag.
3. Juvenile damselfish exposed to 440 (current day control), 550 or 700 µatm CO2 did not differ in their response to the chromis. However, fish exposed to 850 µatm showed reduced antipredator responses; they failed to show the same reduction in foraging, activity and area use in response to the chromis. Moreover, they moved closer to the chromis and lacked any bobbing behaviour typically displayed by juvenile damselfishes in threatening situations.
4. Our results are the first to suggest that response to visual cues of risk may be impaired by CO2 and provide strong evidence that the multi-sensory effects of CO2 may stem from systematic effects at the neural level.

1. 随着全球二氧化碳排放量持续攀升，探究海洋酸化对海洋生态系统影响的研究需求愈发迫切。已有多项研究证实，暴露于二氧化碳环境会损害幼年珊瑚礁鱼类对捕食者的化学感应响应能力。此外，近期一项研究指出，礁栖鱼类对指示危险区域的听觉线索的响应亦出现受损。上述研究提示，高浓度二氧化碳暴露后行为发生改变，其根源可能是神经系统层面的系统性影响。
2. 本实验旨在检验：暴露于不同二氧化碳分压环境下的安邦雀鲷（*Pomacentrus amboinensis*），对潜在威胁——即置于防水袋中的大型新发现珊瑚礁鱼类多棘光鳃鱼（*Acanthochromis polyancanthus*）的视觉呈现——的响应是否存在差异。
3. 暴露于440（当前环境对照）、550或700 µatm二氧化碳环境的安邦雀鲷幼体，其对多棘光鳃鱼的响应并无显著差异。然而，暴露于850 µatm二氧化碳环境的个体，其反捕食响应明显减弱：它们在面对多棘光鳃鱼时，觅食行为、活动水平及活动区域的变化并未出现与对照组一致的降低趋势。此外，它们会更贴近多棘光鳃鱼，且未表现出幼年雀鲷在受威胁情境下典型的摆动行为。
4. 本研究结果首次表明，对风险视觉线索的响应可能会因二氧化碳暴露而受损，并为二氧化碳的多感官影响可能源于神经系统层面的系统性效应提供了强有力的实证支撑。