Seawater carbonate chemistry and metabolic rate, ventilation rate and critical oxygen partial pressure of Dosidicus gigas and Doryteuthis pealeii@en

Ocean acidification is hypothesized to limit the performance of squid owing to their exceptional oxygen demand and pH sensitivity of blood–oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit. In this study, we assessed the effects of CO2 (46–143 Pa; 455–1410 μatm) on the metabolic rate and Pcrit of two squid species - Dosidicus gigas and Doryteuthis pealeii – through manipulative experiments. We also developed a model, with inputs for hemocyanin pH sensitivity, blood PCO2 and buffering capacity, that simulates blood oxygen supply under varying seawater CO2 partial pressures. We compare model outputs with measured Pcrit in squid. Using blood–O2 parameters from the literature for model inputs, we estimated that, in the absence of blood acid–base regulation, an increase in seawater PCO2 to 100 Pa (1000 μatm) would result in a maximum drop in arterial hemocyanin–O2 saturation by 1.6% at normoxia and a Pcrit increase of 0.5 kPa. Our live-animal experiments support this supposition, as CO2 had no effect on measured metabolic rate or Pcrit in either squid species.海洋酸化（Ocean acidification）被学界假设会限制鱿鱼的生理机能，原因在于鱿鱼具备极高的氧需求，且其血液-氧结合过程具有pH敏感性，而酸化水域的氧气供应可能因此受损。临界氧分压（critical oxygen partial pressure, Pcrit）指氧分压（PO2）低于该值时，氧气供应无法满足基础代谢需求，是衡量低氧耐受能力的常用指标。任何由二氧化碳（CO₂）引发的氧气供应下降，均应表现为Pcrit的升高。本研究通过控制性实验，探究了二氧化碳（46–143 Pa；455–1410 μatm）对美洲大赤鱿（Dosidicus gigas）与莱氏拟乌贼（Doryteuthis pealeii）两种鱿鱼的代谢速率与Pcrit的影响。本研究还构建了以血蓝蛋白pH敏感性、血液二氧化碳分压（PCO₂）及缓冲容量为输入参数的模型，可模拟不同海水二氧化碳分压下的血液氧气供应情况，并将模型输出结果与鱿鱼实测的Pcrit进行对比。本研究利用文献中的血液氧相关参数作为模型输入，估算得出：在不存在血液酸碱调节的前提下，当海水PCO₂升高至100 Pa（1000 μatm）时，常氧条件下动脉血蓝蛋白的氧饱和度将最多下降1.6%，且Pcrit将升高0.5 kPa。活体动物实验结果印证了这一假设：二氧化碳对两种鱿鱼的实测代谢速率与Pcrit均无显著影响。