Coral Energy Reserves and Calcification in a High-CO(2) World at Two Temperatures

Rising atmospheric CO(2) concentrations threaten coral reefs globally by causing ocean acidification (OA) and warming. Yet, the combined effects of elevated pCO(2) and temperature on coral physiology and resilience remain poorly understood. While coral calcification and energy reserves are important health indicators, no studies to date have measured energy reserve pools (i.e., lipid, protein, and carbohydrate) together with calcification under OA conditions under different temperature scenarios. Four coral species, Acropora millepora, Montipora monasteriata, Pocillopora damicornis, Turbinaria reniformis, were reared under a total of six conditions for 3.5 weeks, representing three pCO(2) levels (382, 607, 741 µatm), and two temperature regimes (26.5, 29.0°C) within each pCO(2) level. After one month under experimental conditions, only A. millepora decreased calcification (−53%) in response to seawater pCO(2) expected by the end of this century, whereas the other three species maintained calcification rates even when both pCO(2) and temperature were elevated. Coral energy reserves showed mixed responses to elevated pCO(2) and temperature, and were either unaffected or displayed nonlinear responses with both the lowest and highest concentrations often observed at the mid-pCO(2) level of 607 µatm. Biweekly feeding may have helped corals maintain calcification rates and energy reserves under these conditions. Temperature often modulated the response of many aspects of coral physiology to OA, and both mitigated and worsened pCO(2) effects. This demonstrates for the first time that coral energy reserves are generally not metabolized to sustain calcification under OA, which has important implications for coral health and bleaching resilience in a high-CO(2) world. Overall, these findings suggest that some corals could be more resistant to simultaneously warming and acidifying oceans than previously expected.