Coral Reef Laboratory, School of Ocean and Earth Science, University of Southampton, Southampton, United Kingdom; Marine Biology Section, Department of Biology, University of Copenhagen, Helsingør, Denmark; Department of Biological Sciences, National University of Singapore, Singapore, Singapore
Marine Biology Section, Department of Biology, University of Copenhagen, Helsingør, Denmark; Laboratory for Biological Geochemistry, School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
Cecilia D'Angelo
Coral Reef Laboratory, School of Ocean and Earth Science, University of Southampton, Southampton, United Kingdom
Marine Biology Section, Department of Biology, University of Copenhagen, Helsingør, Denmark; Climate Change Cluster, University of Technology Sydney, Sydney, Australia
Department of NanoEngineering, UC San Diego, San Diego, United States; Marine Biological Research Division, Scripps Institution of Oceanography, UC San Diego, San Diego, United States; Bioinspired Photonics Group, Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
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 intra-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 and skeletal reflection 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.
