Is citrate synthase an energy biomarker in Southwestern Atlantic corals? A comparative, biochemical approach under a simulated scenario of climate change

The Southwestern Atlantic (SWA) corals are more tolerant to global warming than those from the Caribbean Sea, possibly due to their higher heterotrophy and flexibility of symbiotic associations in nutrient-rich waters. Increased heterotrophy promotes greater energy gain via increased mitochondrial respiration, which can be used to face unfavorable conditions. Citrate synthase (CS) is a pacemaker enzyme of cellular respiration, and its activity can be used as a proxy for maximum aerobic capacity, thus being a potential predictor of organism tolerance against climate change. Therefore, we hypothesized that endemic coral species from SWA would have higher CS activity than those of pan-Caribbean distribution after exposure to a simulated scenario of moderate climate change (seawater temperature increase: + 2.5 °C; seawater acidification: − 0.3 pH unit), according to IPCC. Seven species of scleractinian corals and one hydrocoral species were biochemically evaluated in a phylogenetic perspective. Favia gravida, Mussismilia harttii, Montastraea cavernosa, Porites astreoides and Siderastrea stellata were unresponsive regarding CS activity, whereas Millepora alcicornis, Mussismilia hispida and Porites branneri showed a compensatory effect. Regardless of their phylogenetic relationships, endemic SWA coral species revealed higher CS activity than those of pan-Caribbean distribution. We suggest that the unique evolutionary history of SWA endemic species contributes to their biochemical tolerance to climate change, thus supporting the hypothesis of SWA as a refuge for reef life. Although CS is not a suitable biomarker for assessing the putative effects of climate change owing to its species-specific responses, it is an informative metric to indicate stress tolerance of species with different biogeographic origins. This idea becomes particularly evident for SWA reefs, where such a comparative, biochemical approach highlights the greater tolerance of endemic species at the subcellular level of organization.