Fig. 4: Two types of coral responses to ocean acidification (OA).
In panel a, the PCA analysis illustrates the two responses identified clustering all samples (n = 4 per species) into two groups with contrasting responses. The first group (blue shade) was represented by O. annularis (dark blue circles), M. cavernosa (blue turquoise circles) and one sample of O. faveolata (orange circles). The second group (green shade) was represented by P. strigosa (red circles) and two samples of O. faveolata (orange circles). A fourth sample of O. faveolata showed very low values in all measured descriptors, indicating low performance for this particular sample. Panel b shows averages ± SE for relative changes in gross photosynthesis, Pmax [blue], calcification, Gmax [mint green]), symbiont [khaki], Chla [green] density, and symbiont cell pigmentation, Ci, [dark green]), for all coral samples of each of the groups identified in the PCA analysis. The first group in blue shade, showed a positive response for host calcification together with slight reductions in symbiont content and holobiont pigmentation. The second group, in green shade, showed positive responses for algal photosynthesis and symbiont content. Asterisks (*) indicate significant differences (t-test; p < 0.05) between the two groups for Pmax (t-test = −4.6, df = 13, p < 0.001), Gmax (t-test = 4.23, df = 13, p < 0.001); symbiont (t-test = 5.1, df = 13, p < 0.001) and pigment density (t-test = −2.7, df = 13, p < 0.02) density. Empty circles represent the values for each sample.
