Mechanical Properties, Spectral Vibrational Response, and Flow-Field Analysis of the Aragonite Skeleton of the Staghorn Coral (Acropora cervicornis)

Authors

Alejandro Carrasco-Pena, University of Central Florida
Mahmoud Omer, University of Central Florida
Bridget Masa, University of Central Florida
Zachary Shepard, University of Central Florida
Tyler Scofield, University of Central Florida
Samik Bhattacharya, University of Central Florida
Nina Orlovskaya, University of Central Florida
Boyce E. Collins, North Carolina A&T University
Sergey N. Yarmolenko, North Carolina A&T University
Jagannathan Sankar, North Carolina A&T University
Ghatu Subhash, University of Florida
David S. Gilliam, Nova Southeastern UniversityFollow
John E. Fauth, University of Central Florida

Document Type

Article

Publication Title

Coral Reefs

ISSN

0722-4028

Publication Date

10-12-2020

Keywords

Compressive strength, Coral nursery, Failure analysis, Microstructure, Raman spectroscopy, Vickers hardness

Abstract

Understanding the structural and mechanical properties of coral skeletons is important to assess their responses to natural and anthropogenic challenges and to predict the long-term viability of hermatypic corals in a changing ocean. Here, we describe the microstructure of the critically endangered staghorn coral (Acropora cervicornis) skeleton and its mechanical properties, spectral and fluidic behavior, including uniaxial compressive strength, resistance to plastic deformation, spectral vibrational response, and flow-field analysis. We evaluated skeletons of A. cervicornis retrieved from a nursery off Broward County, Florida, USA. Optical micrographs and X-ray computed topography revealed a complex system of canals and pores that allow rapid skeletal elongation while retaining sufficient strength to withstand currents, waves, and other physical forces. Compressive loading of the aragonite skeleton resulted in complex stress–strain deformation behavior; the unique pore arrangement resisted catastrophic cracks and prevented instantaneous failure. Vickers microhardness was 3.56 ± 0.31 GPa, which is typical for soft aragonite materials yet sufficient to withstand the hydraulic pressure of ocean waves. Impressions made by the diamond indenter had almost no cracks radiating from their corners, which again demonstrated the ability of the complex skeleton microstructure to suppress crack formation and growth (e.g., from the bites of grazers). Maps of the ν1 mode Raman peak of identation surfaces showed evidence of residual strain. However, the ν1 peak’s position barely changed (from 1083.6 cm−1 outside the impression to 1083.9 cm⁻¹ in the center), indicating weak stress sensitivity. Flow-field analysis revealed small-scale, counter-rotating vortices formed in the skeleton’s wake, which can entrain food particles within range of polyp tentacles and facilitate transport of respiratory gases and wastes. Considered together, our results demonstrate that the perforate skeleton of A. cervicornis is well-adapted to withstand physical forces normally encountered in its shallow-water habitat, but may be susceptible to anthropogenic stressors that alter its architecture.

DOI

10.1007/s00338-020-02003-8

Comments

©Springer-Verlag GmbH Germany, part of Springer Nature 2020

Additional Comments

NSF award #s: 133775, 0959511; US EPA cooperative agreement #: X701D00720

NSUWorks Citation

Alejandro Carrasco-Pena, Mahmoud Omer, Bridget Masa, Zachary Shepard, Tyler Scofield, Samik Bhattacharya, Nina Orlovskaya, Boyce E. Collins, Sergey N. Yarmolenko, Jagannathan Sankar, Ghatu Subhash, David S. Gilliam, and John E. Fauth. 2020. Mechanical Properties, Spectral Vibrational Response, and Flow-Field Analysis of the Aragonite Skeleton of the Staghorn Coral (Acropora cervicornis) .Coral Reefs . https://nsuworks.nova.edu/occ_facarticles/1133.