Acclimatization of a coral-dinoflagellate mutualism at a CO2 vent

• Published in: Communications biology Vol. 6; no. 1; pp. 66 - 10
• Main Authors: Prada, Fiorella, Franzellitti, Silvia, Caroselli, Erik, Cohen, Itay, Marini, Mauro, Campanelli, Alessandra, Sana, Lorenzo, Mancuso, Arianna, Marchini, Chiara, Puglisi, Alessia, Candela, Marco, Mass, Tali, Tassi, Franco, LaJeunesse, Todd C, Dubinsky, Zvy, Falini, Giuseppe, Goffredo, Stefano
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 18.01.2023; Nature Publishing Group UK; Nature Portfolio
• Subjects: Acclimatization; Acidification; Autotrophy; Biology; Carbon dioxide; Corals; Dinoflagellates; Haplotypes; Heterotrophy; Microorganisms; Mutualism; Nitrogen fixation; pH effects; Symbionts
• ISSN: 2399-3642; 2399-3642
• DOI: 10.1038/s42003-022-04327-3

Abstract Ocean acidification caused by shifts in ocean carbonate chemistry resulting from increased atmospheric CO 2 concentrations is threatening many calcifying organisms, including corals. Here we assessed autotrophy vs heterotrophy shifts in the Mediterranean zooxanthellate scleractinian coral Balanophyllia europaea acclimatized to low pH/high pCO 2 conditions at a CO 2 vent off Panarea Island (Italy). Dinoflagellate endosymbiont densities were higher at lowest pH Sites where changes in the distribution of distinct haplotypes of a host-specific symbiont species,  Philozoon balanophyllum, were observed. An increase in symbiont C/N ratios was observed at low pH, likely as a result of increased C fixation by higher symbiont cell densities. δ 13 C values of the symbionts and host tissue reached similar values at the lowest pH Site, suggesting an increased influence of autotrophy with increasing acidification. Host tissue δ 15 N values of 0‰ strongly suggest that diazotroph N 2 fixation is occurring within the coral tissue/mucus at the low pH Sites, likely explaining the decrease in host tissue C/N ratios with acidification. Overall, our findings show an acclimatization of this coral-dinoflagellate mutualism through trophic adjustment and symbiont haplotype differences with increasing acidification, highlighting that some corals are capable of acclimatizing to ocean acidification predicted under end-of-century scenarios.