Data from: Elevated carbon dioxide alters the plasma composition and behaviour of a shark

Increased carbon emissions from fossil fuels are increasing the pCO2 of the ocean surface waters in a process called ocean acidification. Elevated water pCO2 can induce physiological and behavioural effects in teleost fishes, although there appear to be large differences in sensitivity between species. There is currently no information available on the possible responses to future ocean acidification in elasmobranch fishes. We exposed small-spotted catsharks (Scyliorhinus canicula) to either control conditions or a year 2100 scenario of 990 μatm pCO2 for four weeks. We did not detect treatment effects on growth, resting metabolic rate, aerobic scope, skin denticle ultrastructure or skin denticle morphology. However, we found that the elevated pCO2 group buffered internal acidosis via HCO3- accumulation with an associated increase in Na+, indicating that the blood chemistry remained altered despite the long acclimation period. The elevated pCO2 group also exhibited a shift in their nocturnal swimming pattern from a pattern of many starts and stops to more continuous swimming. Although CO2-exposed teleost fishes can display reduced behavioural asymmetry (lateralization), the CO2-exposed sharks showed increased lateralization. These behavioural effects may suggest that elasmobranch neurophysiology is affected by CO2, as in some teleosts, or that the sharks detect CO2 as a constant stressor, which leads to altered behaviour. The potential direct effects of ocean acidification should henceforth be considered when assessing future anthropogenic effects on sharks.

化石燃料碳排放的增加正提升海洋表层水体的二氧化碳分压（pCO2），这一过程被称为海洋酸化。水体二氧化碳分压升高会对硬骨鱼产生生理与行为层面的影响，不过不同物种间的敏感性存在显著差异。目前尚无关于软骨鱼对未来海洋酸化可能产生的响应的相关研究数据。本研究将小斑猫鲨（Scyliorhinus canicula）分别置于对照组与2100年预测的990 μatm pCO2环境中，暴露时长为四周。未观测到实验处理对其生长、静息代谢率、有氧代谢范围、皮肤盾鳞超微结构及盾鳞形态产生显著影响。但研究发现，高pCO2组通过积累碳酸氢根（HCO3-）缓冲体内酸中毒，同时伴随钠离子（Na+）水平升高，表明即便经过长时间驯化，其血液生化指标仍发生了改变。高pCO2组的夜间游泳模式也发生了转变：从频繁启停的模式变为更具连续性的游动。尽管经二氧化碳暴露的硬骨鱼会表现出行为不对称性（偏侧化）减弱的现象，但经二氧化碳暴露的鲨鱼却呈现出偏侧化增强的特征。这些行为层面的影响提示，鲨鱼的神经生理学可能如同部分硬骨鱼一样受到二氧化碳的影响，或是鲨鱼将二氧化碳视为持续存在的胁迫因子，进而导致行为改变。今后在评估人为活动对鲨鱼的未来影响时，应将海洋酸化的潜在直接影响纳入考量范畴。