Mineralogical response of the Mediterranean crustose coralline alga Lithophyllum cabiochae to near-future ocean acidification and warming@en

Red calcareous coralline algae are thought to be among the organisms most vulnerable to ocean acidification due to the high solubility of their magnesium calcite skeleton. Although skeletal mineralogy is proposed to change as CO2 and temperature continue to rise, there is currently very little information available on the response of coralline algal carbonate mineralogy to near-future changes in pCO2 and temperature. Here we present results from a 1-year controlled laboratory experiment to test mineralogical responses to pCO2 and temperature in the Mediterranean crustose coralline alga (CCA) Lithophyllum cabiochae. Our results show that Mg incorporation is mainly constrained by temperature (+1 mol % MgCO3 for an increase of 3 °C), and there was no response to pCO2. This suggests that L. cabiochae thalli have the ability to buffer their calcifying medium against ocean acidification, thereby enabling them to continue to deposit magnesium calcite with a significant mol % MgCO3 under elevated pCO2. Analyses of CCA dissolution chips showed a decrease in Mg content after 1 year for all treatments, but this was affected neither by pCO2 nor by temperature. Our findings suggest that biological processes exert a strong control on calcification on magnesium calcite and that CCA may be more resilient under rising CO2 than previously thought. However, previously demonstrated increased skeletal dissolution with ocean acidification will still have major consequences for the stability and maintenance of Mediterranean coralligenous habitats.红色钙化珊瑚藻因镁方解石（magnesium calcite）骨骼溶解度较高，被认为是最易受海洋酸化（ocean acidification）影响的生物类群之一。尽管有研究提出，随着二氧化碳（CO₂）与温度持续升高，珊瑚藻的骨骼矿物学特征会发生改变，但目前关于珊瑚藻碳酸盐矿物学特征对近未来二氧化碳分压（pCO₂）与温度变化的响应，相关研究仍较为匮乏。本研究以地中海结壳珊瑚藻（crustose coralline alga, CCA）*Lithophyllum cabiochae*为研究对象，开展了为期1年的受控实验室实验，以探究其矿物学特征对二氧化碳分压与温度的响应，并在此报告实验结果。实验结果显示，镁离子掺入量主要受温度调控（温度每升高3℃，碳酸镁摩尔占比提升1 mol%），且不受二氧化碳分压的影响。这表明*L. cabiochae*的藻体可通过对钙化介质进行缓冲以抵御海洋酸化，使其在二氧化碳分压升高的环境中，仍能沉积出具备较高碳酸镁摩尔占比的镁方解石骨骼。对结壳珊瑚藻溶解碎屑的分析表明，经过1年实验后，所有处理组的镁离子含量均出现下降，但该变化既不受二氧化碳分压影响，也不受温度调控。本研究结果提示，生物过程对镁方解石的钙化作用具有极强的调控能力，且结壳珊瑚藻在CO₂升高环境下的抗逆性可能较此前预期更强。然而，此前已证实的海洋酸化会加剧骨骼溶解的现象，仍会对地中海珊瑚藻礁生境的稳定性与维持造成重大影响。