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.

在气候变化背景下，海洋酸化（OA）预计会降低造礁珊瑚的钙化速率，并威胁珊瑚礁的长期生长。当环境二氧化碳分压（pCO2）升高时，珊瑚生长速率的下降可通过足够高的光照强度得到缓冲，但目前学界对OA与光照强度的交互作用对珊瑚生理学其他核心方面（如珊瑚生物量的组成与能量学特征）的影响仍鲜有探究。本研究设置了两种光照处理组（7.5与15.7 mol光子·m⁻²·d⁻¹），并分别在环境pCO2（435 μatm）与升高pCO2（961 μatm）条件下，探究其对夏威夷卡内奥赫湾的造礁珊瑚尖棘杯形珊瑚（Pocillopora acuta）的钙化速率、光色素与共生藻密度、生物量储备（脂质、碳水化合物、蛋白质）以及生物量能量含量（kJ）的影响。尽管pCO2与光照强度对以面积或生物量标准化的钙化速率均无显著影响，但在高pCO2条件下，珊瑚组织的脂质含量（gdw⁻¹）与能量密度（kJ·gdw⁻¹）分别下降了15%与14%；而在高光照条件下，碳水化合物含量上升了15%。高光照与高pCO2的协同处理则使单位面积的蛋白质生物量降低了约20%。因此，在符合生态实际的光照强度下，卡内奥赫湾的尖棘杯形珊瑚并未出现其他珊瑚所报道的、由OA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下降表明，OA诱导了能量亏缺以及珊瑚组织生物量的补偿性分解代谢。两种光照强度下OA对钙化速率无显著影响的实验结果，与越来越多的研究结论相契合——即部分造礁珊瑚可通过补偿性生理机制，维持OA条件下当前的钙化速率水平。然而，OA对尖棘杯形珊瑚生物量组成与能量含量的负面影响，可能会在高pCO2的未来海洋环境中，影响该物种的长期生存表现与生长潜力。