Supplementary Information

Isotropic microscale mechanical properties of coral skeletons

Fig. S1 p. S2

Fig. S2 p. S3

Fig. S3 p. S4

Fig. S4 p. S5

Fig. S5 p. S5

Table S1 p. S6

Table S2 p. S6

Fig. S1. Load-depth curves on a longitudinal B. europaea section, taken in the dry state and in the wet state after soaking for 16 hours in an aragonite-saturated solution.

Fig. S2. (a) Load – depth curves in Continuous Stiffness Measurement mode on the longitudinal B. europaea section; (b) dynamic analysis of the data in (a) yields the Young’s modulus EIT and hardness HIT as a function of indentation depth.

Fig. S3. (a) Load – depth curves in Continuous Stiffness Measurement mode on the longitudinal section of S. pistillata; (b) dynamic analysis of the data in (a) yields the Young’s modulus EIT and hardness HIT as a function of indentation depth.

Fig. S4. Optical images of residual indents (maximum load = 50 mN) recorded in-situ in the nanoindenter. (a)-(b): B. Europaea; (c)-(d): S. Pistillata.

Fig. S5. Optical image of a residual indent (maximum load = 500 mN) on the longitudinal section of B. europaea.

Table S1: Descriptive data and mixed factorial analysis of variance (ANOVA) results for Young’s modulus (EIT) measurements, performed in two different orientations, longitudinal (ln) and transverse (tr), in B. europaea and S. pistillata skeletons.

Species / N / Orientation / Mean EIT (GPa) / SE / 95% Confidence Interval
Lower Bound / Upper Bound
B. europaea / 3 / ln / 77.0 / 1.1 / 74.06 / 79.92
tr / 76.3 / 0.5 / 74.75 / 77.77
S. pistillata / 3 / ln / 76.6 / 1.1 / 73.66 / 79.52
tr / 76.0 / 0.5 / 74.45 / 77.47
Mixed Factorial ANOVA / Type III Sum of Squares / df / Mean Square / F / Sig.
Within-Subjects Contrasts
Orientation / 1.387 / 1 / 1.387 / 0.926 / 0.390
Orientation * Species / 0.007 / 1 / 0.007 / 0.004 / 0.951
Between-Subjects Effects
Species / 0.365 / 1 / 0.365 / 0.134 / 0.733

N: number of skeletons, SE: Standard error

Table S2: Descriptive data and mixed factorial analysis of variance (ANOVA) results for hardness (HIT) measurements, performed in two different orientations, longitudinal (ln) and transverse (tr), in B. europaea and S. pistillata skeletons.

Species / N / Orientation / Mean HIT (MPa) / SE / 95% Confidence Interval
Lower Bound / Upper Bound
B. europaea / 3 / ln / 4870 / 30 / 4787 / 4954
tr / 4970 / 60 / 4799 / 5130
S. pistillata / 3 / ln / 5040 / 30 / 4957 / 5124
tr / 5100 / 60 / 4930 / 5261
Mixed Factorial ANOVA / Type III Sum of Squares / df / Mean Square / F / Sig.
Within-Subjects Contrasts
Orientation / 16699 / 1 / 16699 / 1.722 / 0.260
Orientation * Species / 1139 / 1 / 1139 / 0.117 / 0.749
Between-Subjects Effects
Species / 67868 / 1 / 67868 / 18.811 / 0.012*

N: number of skeletons, SE: Standard error, * p<0.0.

S1