Dissolved inorganic carbon (DIC) assimilation is essential to the reef-building capacity of crustose coralline algae (CCA). Little is known, however, about the DIC uptake strategies and their potential plasticity under ongoing ocean acidification (OA) and warming. The persistence of CCA lineages throughout historical oscillations of pCO₂ and temperature suggests that evolutionary history may play a role in selecting for adaptive traits. We evaluated the effects of pCO₂ and temperature on the plasticity of DIC uptake strategies and associated energetic consequences in reef-building CCA from different evolutionary lineages. We simulated past, present, moderate (IPCC RCP 6.0) and high pCO₂ (RCP 8.5) and present and high (RCP 8.5) temperature conditions and quantified stable carbon isotope fractionation (¹³ε), organic carbon content, growth and photochemical efficiency. All investigated CCA species possess CO₂-concentrating mechanisms (CCMs) and assimilate CO₂ via diffusion to varying degrees. Under OA and warming, CCA either increased or maintained CCM capacity, which was associated with overall neutral effects on metabolic performance. More basal taxa, Sporolithales and Hapalidiales, had greater capacity for diffusive CO₂ use than Corallinales. We suggest that CCMs are an adaptation that supports a robust carbon physiology and are likely responsible for the endurance of CCA in historically changing oceans.

溶解的无机碳（DIC）同化对于壳糖珊瑚藻（CCA）的礁石建造能力至关重要。然而，关于DIC的摄取策略及其在持续的海洋酸化（OA）和变暖下的潜在可塑性知之甚少。在p CO ₂和温度的历史振荡中，CCA谱系的持续存在表明进化史可能在选择适应性状中发挥作用。我们评估了p CO ₂和温度对DIC吸收策略可塑性的影响以及来自不同进化谱系的珊瑚礁构建CCA的相关能量后果。我们模拟了过去，现在，中度（IPCC RCP 6.0）和高p CO ₂（RCP 8.5）和本和高（RCP 8.5）的温度条件和量化的稳定的碳同位素分馏（¹³ ε），有机碳含量，生长和光化学效率。所有调查的CCA物种均具有CO ₂浓缩机制（CCM），并通过不同程度的扩散吸收CO ₂。在OA和变暖下，CCA会增加或保持CCM容量，这与对代谢性能的总体中性影响有关。与Corallinales相比，更多的基础类群，孢子虫和Hapalidiales具有更大的CO ₂扩散使用能力。我们建议CCM是一种适应性强的适应性动物，它支持稳健的碳生理，并且可能对CCA在历史上不断变化的海洋中的承受力负责。