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  • Biomineralization  (1)
  • Raman spectroscopy  (1)
  • 1
    Publication Date: 2019-02-19
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in DeCarlo, T. M., Hen, H., & Farfan, G. A. (2018). The origin and role of organic matrix in coral calcification: Insights from comparing coral skeleton and abiogenic aragonite. Frontiers in Marine Science, 5, (2018): 170. doi:10.3389/fmars.2018.00170.
    Description: Understanding the mechanisms of coral calcification is critical for accurately projecting coral reef futures under ocean acidification and warming. Recent suggestions that calcification is primarily controlled by organic molecules and the biological activity of the coral polyp imply that ocean acidification may not affect skeletal accretion. The basis for these suggestions relies heavily on correlating the presence of organic matter with the orientation and disorder of aragonite crystals in the skeleton, carrying the assumption that organic matter observed in the skeleton was produced by the polyp to control calcification. Here we use Raman spectroscopy to test whether there are differences in organic matter content between coral skeleton and abiogenic aragonites precipitated from seawater, both before and after thermal annealing (heating). We measured the background fluxorescence and intensity of C-H bonding signals in the Raman spectra, which are commonly attributed to coral polyp-derived skeletal organic matrix (SOM) and have been used to map its distribution. Surprisingly, we found no differences in either fluorescence or C-H bonding between abiogenic aragonite and coral skeleton. Annealing reduced the molecular disorder in coral skeleton, potentially due to removal of organic matter, but the same effect was also observed in the abiogenic aragonites. The presence of organic molecules in the abiogenic aragonites is further supported by measurements of N content and δ15N. Together, our data suggest that some of what has been interpreted in previous studies as polyp-derived SOM may actually be seawater-sourced organic matter or some other signal not unique to biogenic aragonite. Finally, we create a high-resolution Raman map of a Pocillopora skeleton to demonstrate how patterns of fluorescence and elevated calcifying fluid aragonite saturation state (ΩAr) along centers of calcification are consistent with both biological and physico-chemical controls. Our aim is to advance discussion on biological mediation of calcification and the implications for coral resilience in a high-CO2 world.
    Description: This study was supported by an ARC Laureate Fellowship (FL120100049) awarded to Professor Malcolm McCulloch and the ARC Centre of Excellence for Coral Reef Studies (CE140100020).
    Keywords: coral ; calcification ; organics ; Raman spectroscopy ; ocean acidification
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Farfan, G. A., Apprill, A., Cohen, A., DeCarlo, T. M., Post, J. E., Waller, R. G., & Hansel, C. M. Crystallographic and chemical signatures in coral skeletal aragonite. Coral Reefs. (2121), https://doi.org/10.1007/s00338-021-02198-4.
    Description: Corals nucleate and grow aragonite crystals, organizing them into intricate skeletal structures that ultimately build the world’s coral reefs. Crystallography and chemistry have profound influence on the material properties of these skeletal building blocks, yet gaps remain in our knowledge about coral aragonite on the atomic scale. Across a broad diversity of shallow-water and deep-sea scleractinian corals from vastly different environments, coral aragonites are remarkably similar to one another, confirming that corals exert control on the carbonate chemistry of the calcifying space relative to the surrounding seawater. Nuances in coral aragonite structures relate most closely to trace element chemistry and aragonite saturation state, suggesting the primary controls on aragonite structure are ionic strength and trace element chemistry, with growth rate playing a secondary role. We also show how coral aragonites are crystallographically indistinguishable from synthetic abiogenic aragonite analogs precipitated from seawater under conditions mimicking coral calcifying fluid. In contrast, coral aragonites are distinct from geologically formed aragonites, a synthetic aragonite precipitated from a freshwater solution, and mollusk aragonites. Crystallographic signatures have future applications in understanding the material properties of coral aragonite and predicting the persistence of coral reefs in a rapidly changing ocean.
    Description: This project was funded by the Mineralogical Society of America Edward H. Kraus Crystallographic Research Fund and the WHOI Ocean Ventures Fund. G. Farfan was supported by a National Science Foundation Graduate Research Fellowship Grant No. 1122374 and a Ford Foundation Dissertation Fellowship. Sample collections from R. Waller were funded under NSF Grant Numbers 1245766, 1127582 and NOAA Ocean Exploration Deep Atlantic Stepping Stones. The authors thank Erik Cordes for the samples collected from the Gulf of Mexico, which were supported by NSF BIO-OCE Grant # 1220478. STZC collections from A. Apprill were funded by a Dalio Foundation (now ‘OceanX’) and a KAUST-WHOI Special Academic Partnership Funding Reserve with Christian Voolstra. Research and coral collections in Cuba were conducted under the LH112 AN (25) 2015 license granted by the Cuban Center for Inspection and Environmental Control with the assistance of Patricia Gonzalez and Michael Armenteros. Corals from Western Australia were collected under license number SF009558 obtained by M. McCulloch, and from the Maldives Ministry of Fisheries and Agriculture with collection permits (No. (OTHR)30-D/INDIV/2013/359). Matthew Neave assisted with the collections.
    Keywords: Aragonite ; Crystallography ; Geochemistry ; Biomineralization ; Environmental mineralogy ; Coral skeleton
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Location Call Number Limitation Availability
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