Linking coral color morphism to thermal tolerance and genomic variation (COLORCODE)

• Applicants: Dr. Rachel Alderdice; Professor Christian Voolstra, Ph.D.
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; General Genetics and Functional Genome Biology ; Oceanography
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556898079

Coral bleaching, i.e. the loss of endosymbiotic photosynthetic algae, is now the main driver of reef decline exacerbated by warming oceans. However, not all corals bleach equally, and it is not fully understood what makes some genotypes in a coral population less susceptible than others. Importantly bleaching is typically driven by heat and light stress during summer months. While this is well acknowledged in the earlier literature, the majority of experimental bleaching studies are now concerned with the effect of thermal stress, disregarding the considerable effect of light (including UV) in contributing to ecologically different bleaching outcomes. Notably, coral can express a range of fluorescent and chromoproteins (i.e., host pigments) that underlie visually distinct color morphs and provide functions related to photoprotection, thermal dissipation, and antioxidant activity (among others). An emergent hypothesis is that differences in host pigment content (i.e., color morphs) contribute to inter- and intra-specific differences in coral thermal tolerance that manifest ecologically in different bleaching susceptibilities. Here we propose to assess how thermal tolerance differences align with the diversity of coral color morphs, their underlying host pigment complements, and their associated endosymbiotic algae, and how such differences in turn map onto the underlying genetic constitution. We suggest doing this by (i) measuring host pigment protein composition of visually distinct color morphs of conspecific coral from a common reef site using a portable spectral profiling setup, (ii) assessing their thermal tolerance thresholds using standardized short-term heat stress assays, (iii) determining their associated endosymbiotic algal assemblage, and (iv) tracking summer bleaching susceptibilities in situ. To obtain insight into their genomic underpinnings, representative colonies of different color morphs will be selected, and their genomes will be sequenced and assembled to (v) perform structural variant analyses of host pigment proteins, which seeks to investigate the molecular basis of color morph differences. In addition to the prospect of better understanding mechanisms that drive inter- and intra-specific thermal tolerance differences, coral color morphs may provide simple yet discriminating "biomarkers" for the identification of thermally tolerant/resilient coral colonies. Outcomes from this research may help to better project bleaching outcomes as well as guide coral restoration efforts, when selecting colonies with increased stress resilience.

• DFG Programme: Research Grants