Holobiont acclimatization dynamics of Pocillopora acuta and Montipora capitata in response to warming and acidification

The rapidly changing environment that surrounds coral reefs is forcing corals to either migrate, acclimatize, or adapt in new, stressful conditions such as ocean warming and acidification. Epigenetic modifications to DNA can alter gene expression and consequently organismal function and phenotype. Additionally, changes in the coral eukaryotic and prokaryotic microbiome can generate phenotypic plasticity. This phenotypic plasticity of the coral holobiont (coral host and microbiome) may result in beneficial or maladaptive phenotypes in these novel environments occurring due to climate change. In an effort to understand acclimatization dynamics, this study exposed a resilient species, Montipora capitata, and sensitive species, Pocillopora acuta, in a factorial experimental design to elevated temperature and pCO2 treatment for 2-months followed by 2-months of recovery. Adult coral performance was assessed via organismal and cellular physiology and molecular response at 1 and 2 days, and 1, 2, 4, 6, 8, 12, and 16 weeks. P. acuta showed greater physiological stress than M. capitata with substantial bleaching, lower survival rates, stunted growth through time, and limited recovery. The combination of RNASeq, DNA methylation (MBD-BS) and microbiome sequencing indicate strong responses to temperature and weaker responses to low pH and greater change in P. acuta than M. capitata. Integrating the physiological and molecular data will further elucidate the timing and extent of response across the different holobiont partners to global change conditions.