Molecular and Skeletal Fingerprints of Scleractinian Coral Biomineralization from the Sea Surface to Mesophotic Depths
41 Pages Posted: 10 Oct 2019 First Look: Accepted
Reef-building corals, the major producers of biogenic calcium carbonate, form skeletons in a plethora of morphological forms. Here we studied skeletal modifications of Stylophora pistillata (clade 4) colonies that dramatically adapt to different depths with decreasing light availability. They show notable transitions from spherical morphologies (shallow depths, 5 m deep) to flat and branching ones (at deep 60 m mesophotic depths). Such changes are typically ascribed to the algal photosymbiont physiological feedback with the coral host. We find typical fine-scale skeletal variability (such as extensive vs. weak development of rapid accretion deposits at shallow- and mesophotic depth morphotypes, respectively) that suggest underlying genetic modifications of biomineralization pathways of the coral host. To explain this, we conducted comparative morphology-based analyses, including microscopy, electron microscopy and spectroscopy coupled with a comprehensive transcriptomic analysis of S. pistillata samples originated from Gulf of Eilat (Red Sea, Israel), collected along a depth gradient from the sea surface (5 m deep) to mesophotic depths (up to 60m). Additional samples were experimentally transplanted from 5m to 60m and from 60m to 5 m. Interestingly, both morphologically and functionally, transplanted corals partly adapt the typical depth-specific properties. In mesophotic depths, we find that the organic matrix fraction is enriched in the coralla, results corroborated by overrepresentation of biomineralization "tool-kit" structural extracellular genes. These results provide insights into the molecular mechanisms of coral calcification and skeletal adaptation that repeatedly allowed this group to adapt to extreme environments now and in geological past.
Keywords: Bioinfomatics/Phyloinfomatics, Cnidarians, Mesophotic Reef, Biomineralization, morphology plasticity, Electron microscopy, micro CT, high-resolution synchrotron X-ray powder diffraction
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