Effects of increasing temperature alone and combined with copper exposure on biochemical and physiological parameters in the zooxanthellate scleractinian coral Mussismilia harttii

Effects of increasing temperature alone and in combination with exposure to dissolved copper (Cu) were evaluated in the zooxanthellate scleractinian coral Mussismilia harttii using a marine mesocosm system. Endpoints analyzed included parameters involved in metabolism [maximum photosynthetic capacity of zooxanthellae (Fv/Fm), chlorophyll a and ATP concentrations], calcification [carbonic anhydrase (CA) and Ca²⁺-Mg²⁺-ATPase activity], and oxidative status [antioxidant capacity against peroxyl radicals (ACAP) and lipid peroxidation (LPO)]. Coral polyps were collected, acclimated and exposed to three increasing temperature conditions [25.0 ± 0.1 °C (control; average temperature of local seawater), 26.6 ± 0.1 °C and 27.3 ± 0.1 °C] using a marine mesocosm system. They were tested alone and in combination with four environmentally relevant concentrations of dissolved Cu in seawater [2.9 ± 0.7 (control; average concentration in local seawater), 3.8 ± 0.8, 5.4 ± 0.9 and 8.6 ± 0.3 μg/L] for 4, 8 and 12 days. Fv/Fm reduced over the experimental period with increasing temperature. Combination of increasing temperature with Cu exposure enhanced this effect. CA and Ca²⁺-Mg²⁺-ATPase activities increased up to 8 days of exposure, but recovered back after 12 days of experiment. Short-term exposure to increasing temperature or long-term exposure to the combination of stressors reduced LPO, suggesting the occurrence of a remodeling process in the lipid composition of biological membranes. ACAP, ATP and chlorophyll a were not significantly affected by the stressors. These findings indicate that increasing temperature combined with exposure to dissolved Cu increase susceptibility to bleaching and reduce growth in the zooxanthellate scleractinian coral M. harttii.