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

Abstract

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.

Short-Term Thermal Acclimation Modifies the Metabolic Condition of the Coral Holobiont

“…The coral species that we used in this study, Pocillopora damicornis, lives close to its thermal maximum in Kaneohe Bay, Hawaii and is usually among the most bleaching-susceptible species in the region (Jokiel and Brown, 2004;Bahr et al, 2015). Comparison of our values with those reported in previous studies, revealed that our photosynthesis and respiration rates and the symbiont densities were substantially less for P gross and R; (Lesser et al, 1994) and symbiont density (Stimson and Kinzie, 1991;Wall et al, 2017); than usual for P. damicornis, yet we observed no visible signs of bleaching. Acclimation temperature had little effect on final holobiont level measurements: with no detectable differences between the O 2 -budget (both P gross and R) of ambient and warm-acclimated corals, and negligible differences in symbiont density and total chlorophyll content per symbiont cell.…”

Spatial variation in the biochemical and isotopic composition of corals during bleaching and recovery

“…Fragments were immediately frozen in liquid nitrogen 171 and stored at -80 °C until processing. 172 173 All biomass assays were performed on the holobiont tissues (host + symbionts), following 174 established procedures (Wall et al 2017). Additional information methodology information can 175 be found in the Supporting Information.…”

Paradise lost: End‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

“…lobata. The introduction of symbiont-specific traits and other varying factors may lead to trade-offs in coral performance (Jones & Berkelmans, 2011), and invites further experiments studying different combinations of environments and organisms to discern future climate impacts on reef health and survival (Bay et al, 2017;Hoadley et al, 2019;Wall, Mason, Ellis, Cunning, & Gates, 2017). Our results show that P. lobata is more tolerant to thermal and OA stress than A. intermedia.…”