Elevated p CO 2 affects tissue biomass composition, but not calcification, in a reef coral under two light regimes

• Published in: Royal Society Open Science
• Main Authors: Wall, C. B., Mason, R. A. B., Ellis, W. R., Cunning, R., Gates, R. D.
• Other Authors: UH Graduate Opportunity Grant, the UH Edmondson Research Fund, and Environmental Protection Agency (EPA) STAR Fellowship Assistance Agreement, NSF Postdoctoral Fellowship in Biology
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2017
• Subjects: Ocean acidification
• Online Access: http://dx.doi.org/10.1098/rsos.170683; https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.170683; https://royalsocietypublishing.org/doi/full-xml/10.1098/rsos.170683

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 p CO 2 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 p CO 2 (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 p CO 2 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 p CO 2 , and carbohydrate content increased 15% under high light. The combination of high light and high p CO 2 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 p CO 2 world.