Figure 1.
Light transport in coral skeletons.
A – Visual demonstration of differences in light transport shown for three taxa as described in [10] by focusing a laser on (a) highly-absorbing black surface and on skeletons of (b) Leptastrea transversa, (c) Leptoria phrygia, and (d) Seriatopora caliendrum. Microscopic light-scattering properties of skeletons were measured using LEBS with a white light source. B – Schematic representation of the redistribution of light between sun-exposed versus shaded areas. Differences in light transport are shown for corals with (a) very high skeleton and a (b) low
skeleton. Skeletons capable of longer light transport (i.e. longer
or low
) are able to illuminate otherwise shaded areas in the colony and this increased redistribution between sun-exposed versus shaded areas of a colony may further amplify the light available to the algae: (I) downwelling light, (II) diffuse reflectance, (III) photon path (arrows) and sub-micron scatters (black dots), (IV) diffuse reflectance illuminating a shaded algal cell in the coral tissue: the skeleton serves as a secondary light source [9].
Figure 2.
A – Relationship between excess light (E) and concentration of absorbing particles (ρ). Data collected using ‘flat coral models’: Bottom layer: ∼1 mm skeleton slices (Pocillopora damicornis - open circles; Seriatopora hystrix - squares, Porites lobata - diamonds) on top of a highly scattering standard or the standard alone - triangles. Top layer: set of five 1 mm polymer layers containing progressively lower concentrations of fluorescent 6 µm microspheres (ρ) mimicking light absorbing symbionts densities in healthy tissue (100% cover = 7.8×106 microspheres/cm2) and in corals undergoing bleaching response up to 93% bleached (0.7×106 microspheres/cm2). B – association with the rate of excess light increase (ΔE) for 13 skeletons of 10 coral species. ΔE was calculated for each ‘flat coral’ construct from data as in Fig. 2A.
Figure 3.
Relationship between and bleaching response index (BRI).
Data organized into low (31 taxa, BRI = 18.42±0.82%, mean ±SE), medium (48 taxa, BRI = 36.35±0.53%) and high (17 taxa, BRI = 57.27±1.5%) BRI clusters; ANOVA, p<0.002.
Figure 4.
Evolutionary correlation between scattering coefficient and coral bleaching.
A composite phylogeny shown in mirror image, with character states for (left) and BRI (right) mapped to illustrate their significant correlation (p<0.05) throughout the evolutionary history of corals. High bleaching susceptibility appears to be less common toward the base of the coral tree (box A) and higher in the Montipora-Acropora clade (box B) and the “Robusta” coral clade (box C).
Figure 5.
Relationship between growth-form averaged- and fractal dimension (Df).
Example colonies of various growth forms: (a) thin-branching: Seriatopora hystrix, (b) medium-branching: Stylophora subseriata, and (c) thick-branching Acropora variolosa (average diameter of branches shown in figure), (d) laminar/foliaceous: Echinopora lamellosa and (e) massive: Galaxea sp.
Figure 6.
Fractal dimension of different biogenic (biomineralized) and non-biogenic materials as measured by LEBS.