Data from: Elevated pCO2 affects tissue biomass composition, but not calcification, in a reef coral under two light regimes

Ocean acidification (OA) is predicted to reduce reef coral calcification rates and threaten the long-term growth of coral reefs under climate change. Reduced coral growth at elevated pCO2 may be buffered by sufficiently high irradiances; however, the interactive effects of OA and irradiance on other fundamental aspects of coral physiology, such as the composition and energetics of coral biomass, remain largely unexplored. This study tested the effects of two light treatments (7.5 versus 15.7 mol photons m−2 d−1) at ambient or elevated pCO2 (435 versus 957 µatm) on calcification, photopigment and symbiont densities, biomass reserves (lipids, carbohydrates, proteins), and biomass energy content (kJ) of the reef coral Pocillopora acuta from Kāne‘ohe Bay, Hawai‘i. While pCO2 and light had no effect on either area- or biomass-normalized calcification, tissue lipids gdw−1 and kJ gdw−1 were reduced 15% and 14% at high pCO2, and carbohydrate content increased 15% under high light. The combination of high light and high pCO2 reduced protein biomass (per unit area) by approximately 20%. Thus, under ecologically relevant irradiances, P. acuta in Kāne‘ohe Bay does not exhibit OA-driven reductions in calcification reported for other corals; however, reductions in tissue lipids, energy content and protein biomass suggest OA induced an energetic deficit and compensatory catabolism of tissue biomass. The null effects of OA on calcification at two irradiances support a growing body of work concluding some reef corals may be able to employ compensatory physiological mechanisms that maintain present-day levels of calcification under OA. However, negative effects of OA on P. acuta biomass composition and energy content may impact the long-term performance and scope for growth of this species in a high pCO2 world.

海洋酸化（Ocean acidification, OA）被预测将在气候变化背景下降低礁珊瑚的钙化速率，并威胁珊瑚礁的长期存续。在升高的二氧化碳分压（pCO₂）环境中，珊瑚生长受到的抑制或可通过充足的高辐照度得到缓冲；然而，海洋酸化与辐照度的交互作用对珊瑚生理学其他核心维度的影响，例如珊瑚生物量的组成与能量学特征，目前仍未得到充分探究。本研究以采自夏威夷卡内奥赫湾的鹿角杯形珊瑚（Pocillopora acuta）为研究对象，设置两种光照处理（7.5与15.7 mol光子·m⁻²·d⁻¹），并分别设置环境（435 μatm）与升高（957 μatm）两组二氧化碳分压条件，探究其对钙化作用、光合色素（photopigment）与共生体密度、生物量储备（脂质、碳水化合物、蛋白质）以及生物量能量含量（单位：kJ）的影响。尽管二氧化碳分压与光照对单位面积或单位生物量标准化后的钙化速率均无显著影响，但高二氧化碳分压环境下，单位组织干重的脂质含量与能量含量分别降低15%与14%；而高光辐照度条件下，碳水化合物含量提升15%。高光与高二氧化碳分压的联合作用会使单位面积的蛋白质生物量降低约20%。综上，在符合生态实际的辐照度条件下，卡内奥赫湾的鹿角杯形珊瑚并未出现其他珊瑚所报道的、由海洋酸化驱动的钙化速率降低现象；但组织脂质、能量含量与蛋白质生物量的减少表明，海洋酸化诱发了能量赤字与组织生物量的补偿性分解代谢。海洋酸化在两种辐照度下对钙化作用无显著影响的结果，与日益增多的研究结论相符，即部分礁珊瑚或许能够启动补偿性生理机制，以在海洋酸化环境中维持当前的钙化水平。然而，海洋酸化对鹿角杯形珊瑚生物量组成与能量含量的负面影响，可能会影响该物种在高二氧化碳分压未来环境中的长期生存能力与生长潜力。