Coral reefs are threatened by global and local impacts, such as ocean acidification (OA) and metal contamination. Toxicity of metals, such as copper (Cu), is expected to be enhanced with OA. However, the interaction between these environmental stressors is still poorly evaluated. In the present study, the interactive effects of seawater acidification and increasing Cu concentrations were evaluated in a zooxanthellate scleractinian coral (Mussismilia harttii), using biochemical biomarkers involved in the coral calcification process and the photosynthetic metabolism of endosymbionts. Corals were kept under control conditions (no seawater acidification and no Cu addition in seawater) or exposed to combined treatments of reduced seawater pH (8.1, 7.8, 7.5 and 7.2) and environmentally relevant concentrations of dissolved Cu (measured: 1.0, 1.6, 2.3 and 3.2 μg/L) in a mesocosm system. After 15- and 35-days exposure, corals were analyzed for photochemical efficiency (Fv/Fm), chlorophyll a content, Ca-ATPase and carbonic anhydrase (CA) activity. Results showed that 76% of the interactions between reduced seawater pH and increasing Cu concentrations were antagonistic. Only 24% of these interactions were additive or synergistic. In general, the combination of stressors had no significant deleterious effects in the photosynthetic metabolism of endosymbionts or Ca-ATPase activity. In fact, the lowest dissolved Cu concentration tested had a consistent positive effect on Ca-ATPase activity in corals facing any of the reduced seawater pH conditions tested. In turn, potentially deleterious effects on acid-base balance in M. harttii, associated with changes in CA activity, were intensified by the combination of stressors. Findings reported here indicate that Cu toxicity in future OA scenarios can be less severe than previously suggested in this coral holobiont.

珊瑚礁受到全球和当地影响的威胁，例如海洋酸化（OA）和金属污染。OA有望提高金属（如铜（Cu））的毒性。但是，这些环境压力源之间的相互作用仍然评价不佳。在本研究中，评估了在动物黄藻的巩膜珊瑚（Mussismilia harttii）中海水酸化和铜浓度增加的相互作用。），使用涉及珊瑚钙化过程和共生内膜的光合代谢的生化生物标记。将珊瑚置于控制条件下（无海水酸化，海水中无铜添加）或暴露于降低的海水pH值（8.1、7.8、7.5和7.2）和与环境相关的溶解铜浓度（测得：1.0、1.6、2.3）的联合处理中和3.2μg/ L）。暴露15天和35天后，分析了珊瑚的光化学效率（F v / F m），叶绿素a含量，Ca-ATPase和碳酸酐酶（CA）活性。结果表明，海水pH降低和铜浓度增加之间的相互作用中有76％是拮抗性的。这些相互作用中只有24％是加性或协同作用。通常，应激源的组合对共生菌的光合代谢或Ca-ATPase活性没有明显的有害影响。实际上，面对任何降低的海水pH条件，所测试的最低溶解Cu浓度对珊瑚中的Ca-ATPase活性具有一致的积极影响。反过来，对哈氏甲烷八叠球菌酸碱平衡的潜在有害影响应激源的组合加剧了与CA活动变化相关的。此处报道的发现表明，在未来的OA情景中，Cu的毒性可能不如以前在该珊瑚万寿菊中所建议的那么严重。