Wiedenmann, J. | Search bioRxiv

bioRxiv2026

In vivo X-ray Computed Microtomography: A Novel Approach to Assess Coral Skeletal Construction

Scleractinian (stony) corals build reef frameworks through calcium carbonate deposition, yet all methods for assessing skeletal growth - staining, SEM, or ex vivo {micro}CT - are limited to endpoint measurements on dead specimens. Here, we utilise in vivo X-ray computed microtomography ({micro}CT) to non-destructively quantify skeletal growth in the reef-building coral Stylophora pistillata for the first time. Our in vivo {micro}CT approach applied to one individual over 16 days revealed a volume increase from [~]630 to [~]700 mm3 that can be partitioned into external vertical extension and internal lateral thickening, generating high-resolution 4D reconstructions of the evolving skeletal architecture. These measurements were consistent with established approaches but provide additional unique insights into internal growth dynamics. We demonstrate that in vivo CT enables micron-scale monitoring of calcification processes of living stony corals, thereby representing a powerful new tool to probe coral growth dynamics in the face of rapidly changing environmental conditions.

bioengineering↗

bioRxiv2021

Green fluorescent protein-like pigments optimize the internal light environment in symbiotic reef building corals

Pigments homologous to the Green Fluorescent Protein (GFP) have been proposed to fine-tune the internal light microclimate of corals, facilitating photoacclimation of photosynthetic coral symbionts (Symbiodiniaceae) to life in different reef habitats and environmental conditions. However, direct measurements of the in vivo light conditions inside the coral tissue supporting this conclusion are lacking. Here, we quantified the intra-tissue spectral light environment of corals expressing GFP-like proteins from widely different light regimes. We focus on (1) photoconvertible red fluorescent proteins (pcRFPs), thought to enhance photosynthesis in mesophotic habitats via wavelength conversion, and (2) chromoproteins (CPs), which provide photoprotection to the symbionts in shallow water via light absorption. Optical microsensor measurements indicated that both pigment groups strongly alter the coral tissue light environment. Estimates derived from light spectra measured in pcRFP-containing corals showed that fluorescence emission can contribute to >50% of orange-red light available to the photosynthetic symbionts at mesophotic depths. We further show that upregulation of pink CPs in shallow-water corals during bleaching leads to a reduction of orange light by 10-20% compared to low-CP tissue. Thus, screening by CPs has an important role in mitigating the light-enhancing effect of coral tissue scattering during bleaching. Our results provide the first experimental quantification of the importance of GFP-like proteins in fine-tuning the light microclimate of corals during photoacclimation.

ecology↗