Seawater carbonate chemistry and acid–base balance in the hæmolymph of European abalone (Haliotis tuberculata)@en

Ocean acidification (OA) and the associated changes in seawater carbonate chemistry pose a threat to calcifying organisms. This is particularly serious for shelled molluscs, in which shell growth and microstructure has been shown to be highly sensitive to OA. To improve our understanding of the responses of abalone to OA, this study investigated the effects of CO2-induced ocean acidification on extra-cellular acid–base parameters in the European abalone Haliotis tuberculata. Three-year-old adult abalone were exposed for 15 days to three different pH levels (7.9, 7.7, 7.4) representing current and predicted near-future conditions. Hæmolymph pH and total alkalinity were measured at different time points during exposure and used to calculate the carbonate parameters of the extracellular fluid. Total protein content was also measured to determine whether seawater acidification influences the composition and buffer capacity of hæmolymph. Extracellular pH was maintained at seawater pH 7.7 indicating that abalones are able to buffer moderate acidification (−0.2 pH units). This was not due to an accumulation of HCO3− ions but rather to a high hæmolymph protein concentration. By contrast, hæmolymph pH was significantly decreased after 5 days of exposure to pH 7.4, indicating that abalone do not compensate for higher decreases in seawater pH. Total alkalinity and dissolved inorganic carbon were also significantly decreased after 15 days of low pH exposure. It is concluded that changes in the acid–base balance of the hæmolymph might be involved in deleterious effects recorded in adult H. tuberculata facing severe OA stress. This would impact both the ecology and aquaculture of this commercially important species.海洋酸化（Ocean Acidification, OA）及其伴随的海水碳酸盐化学变化对钙化生物构成威胁，这对带壳软体动物尤为严重——已有研究表明，这类生物的贝壳生长与微观结构对OA极为敏感。为加深对鲍鱼响应海洋酸化机制的理解，本研究探究了CO₂诱导的海洋酸化对欧洲鲍（Haliotis tuberculata）细胞外酸碱参数的影响。实验选取3龄成年欧洲鲍，将其置于3种不同pH水平（7.9、7.7、7.4）的水环境中暴露15天，这3种pH分别代表当前及预测的近期未来海水pH条件。在暴露过程中的不同时间点，研究人员测定了其血淋巴pH与总碱度，并据此计算细胞外液的碳酸盐参数；同时测定总蛋白含量，以分析海水酸化是否会影响血淋巴的组成与缓冲能力。研究发现，当海水pH为7.7时，欧洲鲍的细胞外pH得以维持，表明其能够缓冲中等程度的酸化（pH降低0.2单位）；该缓冲效应并非源于HCO₃⁻离子的积累，而是依赖于较高的血淋巴蛋白浓度。与之相反，当暴露于pH7.4的水环境中5天后，血淋巴pH出现显著下降，说明欧洲鲍无法补偿海水pH的大幅降低。在低pH环境中暴露15天后，血淋巴的总碱度与溶解无机碳也均出现显著下降。综上，血淋巴酸碱平衡的紊乱可能与成年欧洲鲍在严重OA胁迫下出现的有害效应相关，这将对这一具有重要商业价值物种的生态学与水产养殖业产生影响。