Data from: Fluctuating seawater pH/ p CO 2 regimes are more energetically expensive than static pH/ p CO 2 levels in the mussel Mytilus edulis

Ocean acidification (OA) studies typically use stable open-ocean pH or CO2 values. However, species living within dynamic coastal environments can naturally experience wide fluctuations in abiotic factors, suggesting their responses to stable pH conditions may not be reflective of either present or near-future conditions. Here we investigate the physiological responses of the mussel Mytilus edulis to variable seawater pH conditions over short- (6 h) and medium-term (2 weeks) exposures under both current and near-future OA scenarios. Mussel haemolymph pH closely mirrored that of seawater pH over short-term changes of 1 pH unit with acidosis or recovery accordingly, highlighting a limited capacity for acid–base regulation. After 2 weeks, mussels under variable pH conditions had significantly higher metabolic rates, antioxidant enzyme activities and lipid peroxidation than those exposed to static pH under both current and near-future OA scenarios. Static near-future pH conditions induced significant acid–base disturbances and lipid peroxidation compared with the static present-day conditions but did not affect the metabolic rate. These results clearly demonstrate that living in naturally variable environments is energetically more expensive than living in static seawater conditions, which has consequences for how we extrapolate future OA responses in coastal species.海洋酸化（OA）研究通常采用稳定的开阔海域海水pH或二氧化碳浓度值。然而，栖息于动态海岸环境中的海洋生物会自然经历非生物因子的剧烈波动，这表明它们对稳定pH条件的响应或许无法反映当前乃至不久将来的实际环境状况。本研究以紫贻贝（Mytilus edulis）为研究对象，探究其在当前及不久将来海洋酸化情景下，经短期（6小时）、中期（2周）暴露于可变海水pH条件后的生理响应。在短期1个pH单位的酸化或恢复性变化过程中，贻贝血淋巴pH与海水pH高度同步，凸显出其酸碱调节能力有限。暴露2周后，在当前及不久将来海洋酸化情景下，可变pH组贻贝的代谢速率、抗氧化酶活性及脂质过氧化水平均显著高于恒定pH组贻贝。与当前恒定pH条件相比，不久将来的恒定pH条件会引发显著的酸碱紊乱与脂质过氧化，但不会对代谢速率产生影响。本研究结果清晰表明，相较于恒定海水环境，栖息于自然动态环境中的生物所需的能量成本更高，这一结论将对我们外推海岸物种未来海洋酸化响应的方式产生重要影响。