A unique coral biomineralization

pattern has resisted 40 million

years of major ocean chemistry

changeJarosław Stolarski, Francesca R. Bosellini, Carden C. Wallace, Anne M. Gothmann, Maciej Mazur, Isabelle Domart-Coulon, Eldad Gutner-Hoch, Rolf D. Neuser, Oren Levy, Aldo Shemesh & Anders Meibom

Journal: Scientific ReportsPublished: 15 June 2016Impact Factor: 5.228DOI: 10.1038/srep27579

Presented by:Akansha Ganguly

MBT IIMB0415

5th August, 2016Department of Biotechnology,

Goa University

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ContentsIntroductionMaterials and MethodsResults and DiscussionConclusionReferences

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Introduction• Scleractinia (scler = hard, actinia = ray) – marine polyps, secrete a hard skeleton.

Two subgroups – reef-builders (e.g. Acroporidae), non-reef-building corals (Tubastraea coccinea).• Acropora - best-studied scleractinian coral genera, taxonomy, biogeography,

physiology, reproduction, biomineralization investigated. • Fine-scale details studied in ultrastructure: highly distinct, scale-like (shingle)

organization of skeletal thickening deposits (TD). • Biomineralization process controlled with functional macromolecules (proteins,

sulphated polysaccharides); direct control over mineralogy, crystallographic properties, trace-element and isotopic (e.g. δ15N) compositions of the resulting aragonitic structures.

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Materials and Methods• Structural analyses- Polished sections observed under polarized light and transmitted light. - Skeletons (extant/fossilized) etched with 0.1% formic acid, rinsed, dried observed under Phillips

XL20 scanning electron microscope.• Growth and 86Sr labelling experiments- A. eurystoma fragments labelled in 12h pulses in 500 mL seawater enriched with 10 mg/L

dissolved 86SrCO3. - Nubbins snap-frozen at -800C to stop metabolic and biomineralization processes. - 86Sr/44Ca distribution mapped with NanoSIMS ion microprobe.• Trace element analyses- Trace element (Mg/Ca) analyses with NanoSIMS ion microprobe on polished and gold-coated

(20 nm) skeletal surfaces embedded in epoxy-resin with 5 µm step-size.

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Results and Discussion

Figure 1. Skeleton texture and structure in Recent Acroporaa. A. eurystoma branch (lateral view)b. Shingle formation along direction of extensional structure c. Incremental growth lines of shingles in thin-sectioned skeleton of A.

muricatad,e. Distal portions of coenosteal spinulae and short septal spinesf,g. Extremely slender bundles of fibers form the edge of the growing front of shingles in A. muricata

1.

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2.

Figure 2. Microstructure and differentiation of shingles near the tip of coenosteal spinulae visualized by 86Sr labelling in Recent Acropora (A. eurystoma)a. longitudinal section along the fast

growing skeletal regions, includes spinulae (yellow arrows), rapid accretion deposits - RAD (red arrows) and shingles (blue arrows)

b,c. Ultrathin transverse section (b), polarized light)), polished, slightly etched section (c) : longitudinal sections of bundles of fibers several hundreds of micrometers long, suggesting continuous growth of individual shingles

d,e. NanoSIMS 86Sr/44Ca isotope mosaic map, SEM image of polished and etched sample

f. NanoSIMS and SEM images overlaid.

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3. Figure 3. Example of good preservation of skeletal features (mineralogy, surface texture andmicrostructure) in fossil Acropora.a. transverse section of coral branch, white rectangle (enlargement in (d))b. Enlargment of fossil surface, (c) with desmocyte attachment scarse,f. Shingled thickening deposits (TD), still discernible, though erodedg,h. Micro-Ramanmaps of region indicated in (d) aragonite lattice mode at 203 cm−1 (g), and carbonate vibrational mode at 1085 cm−1 (h) showing aragonite skeletoni. Contact zone (polished and etched surface) between RAD and TD (shingles) deposits

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4. Figure 4. Evolutionary continuity of shingle-like biomineralization pattern in Acropora lineage.(a–d). Direct comparison of microstructural features of modern (a) and fossil (b–d) aragonite skeletons ofAcropora showing evidence of growing shingles. Shown: ultra-thin transverse sections (polarized transmitted light) of: (a) extant A. muricata, (b) Miocene (Burdigalian) A. exerata (c) Miocene (Aquitanian) Acropora sp. (d) Middle Eocene A. alvarezi e. regular incremental growth lines (yellow arrows) in shingled thickening deposits in Miocene (Aquitanian) Acropora sp.

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Figure 5. Evolutionary continuity of shingle-like biomineralization pattern in Acropora lineage acrossgeochemical gradients. • Grey circles - Seawater Mg/Ca

composition during last 100 Ma inferred from diverse well preserved fossil corals

• Red circles - Mg/Ca of seawater inferred from extant and best preserved aragonite fossil Acropora samples.

• Red graph line - seawater Mg/Ca reconstruction

• Green curve - estimates of atmospheric CO2 reconstructed from terrestrial and marine proxies.

• Horizontal green line - present-day atmospheric CO2 concentration (ca. 400 ppm).

(Conventional boundary of aragonite and calcite precipitation - Mg/Ca= 2)

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Conclusion• Scleractinians exert partial control over skeletal mineralogy• Acropora lineage maintained remarkable evolutionary stability with regard

to both skeletal mineralogy and biomineralization pattern despite the major Mg/Ca fluctuations in the Cenozoic• Corals accommodate relatively slow Mg/Ca fluctuations; acroporids formed

aragonitic skeletons across the Paleocene-Eocene and Oligocene-Miocene epochs although skeletons also registered the changing Mg/Ca ratio of seawater geochemistry• Marine biogenic carbonate fossils - well-preserved acroporid skeletons

represent material with very high potential for reconstruction of ancient ocean chemistry

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References• Hayward, D. C. et al. Differential Gene Expression at Coral Settlement and Metamorphosis - A

Subtractive Hybridization Study. PLoS ONE 6, e26411 (2011)• Horita, J., Zimmermann, H. & Holland, H. D. Chemical evolution of seawater during the

Phanerozoic: Implications from the record of marine evaporites. Geochim. Cosmochim. Acta 66, 3733–3756 (2002)

• Bice, K. L., Layne, G. D. & Dahl, K. Application of secondary ion mass spectrometry to the determination of Mg/ Ca in rare, delicate, or altered planktonic foraminifera: examples from the Holocene, Paleogene, and Cretaceous. Geochem. Geophys. Geosyst. 6, Q12P07 (2005)

• Houlbreque, F. et al. Strontium-86 labelling experiments show spatially heterogeneous skeletal formation in the scleractinian coral Porites porites. Geophys. Res. Lett. 36, L04604 (2009)

• Brahmi, C. et al. Pulsed 86Sr-labeling and NanoSIMS imaging to study coral biomineralization at ultra-structural length scales. Coral Reefs 31, 741–752 (2012)