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 vs. 15.7 mol photons m-2 d-1) at ambient- or elevated-pCO2 (435 vs. 961 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 ~ 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造礁珊瑚的钙化速率，并威胁珊瑚礁的长期生长。在升高的二氧化碳分压（pCO₂）条件下，珊瑚生长速率的下降可通过足够高的辐照度得到缓冲；然而，海洋酸化与辐照度对珊瑚生理学其他核心维度的交互影响——例如珊瑚生物量的组成与能量学特征——仍未得到充分探索。本研究以采自夏威夷卡内奥赫湾（Kāne‘ohe Bay）的尖枝列孔珊瑚（Pocillopora acuta）为研究对象，设置了两种光照处理（7.5 与 15.7 mol 光子 m⁻² d⁻¹）以及两种二氧化碳分压条件（环境水平：435 μatm、升高水平：961 μatm），探究其对珊瑚钙化速率、光合色素与共生体密度、生物量储备（脂质、碳水化合物、蛋白质）以及生物量能量含量（千焦，kJ）的影响。研究结果显示，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；但在高二氧化碳分压条件下，每克干重（gdw⁻¹）的组织脂质含量与能量含量分别下降15%与14%，而高光辐照条件下的碳水化合物含量上升15%。高光辐照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下降约20%。综上，在符合生态现实的辐照度条件下，卡内奥赫湾的尖枝列孔珊瑚并未出现此前在其他珊瑚物种中报道的、由海洋酸化驱动的钙化速率下降现象；但组织脂质、能量含量与蛋白质生物量的降低表明，海洋酸化会诱导该珊瑚出现能量亏空，并引发组织生物量的补偿性分解代谢。海洋酸化在两种辐照度条件下对钙化速率均无显著影响的结果，佐证了日益增多的研究结论：部分造礁珊瑚或可通过补偿性生理机制，维持海洋酸化背景下当前的钙化速率水平。然而，海洋酸化对尖枝列孔珊瑚生物量组成与能量含量的负面影响，或会影响该物种在高二氧化碳分压未来海洋中的长期生存性能与生长潜力。