Environmental impact on the mechanical properties of Porites spp. corals

Molly A Moynihan, Shahrouz Amini, Nathalie F Goodkin, Jani T I Tanzil, J Q Isaiah Chua, Gareth N Fabbro, Tung-Yung Fan, Daniela N Schmidt, Ali Miserez

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Hard corals (Scleractinia) construct structurally complex environments that serve as critical habitat for marine organisms and provide storm protection to coastal populations. Despite the economic and ecological importance of corals’ skeletal structure, as well as their predicted vulnerability to future climate change, few studies have examined the skeletal mechanicalpropertiesatthenanoscale.Moreover,whilematerialpropertiesareintimatelylinkedtothechemicalcomposition of the skeleton, no previous study has examined mechanical properties alongside carbonate geochemical composition. Using Porites coral cores from a wide range of reef environments (Thailand, Singapore, Taiwan), we correlated coral’s micro-mechanical properties with chemical composition. We document unprecedented variability in the hardness, stiffness, and micro-cracking stress of Porites corals across reef environments, which may significantly decrease the structural integrity of reef substrate. Corals from environments with low salinity and high sedimentation have higher organic content and fracture at lower loads, suggesting that skeletal organic content causes enhanced embrittlement. Within individual coral cores, we observe seasonal variability in skeletal stiffness, and a weak trend between high sea surface temperature, increased stiffness, and high-density. Regionally, lower Sr/Ca and higher Mg/Ca coincide with decreased stiffness and hardness, which is likely driven by increased amorphous calcium carbonate and skeletal organic content. If the coral is significantly embrittled, as measured here in samples from Singapore, faster erosion is expected. A decrease in skeletal stiffness will decrease the quality of reef substrate, enhance the rate of bioerosion by predators and borers, and increase colony dislodgement and macro-scale reef damage.
Original languageEnglish
JournalCoral Reefs
Publication statusAccepted/In press - 9 Oct 2020

Keywords

  • mechanical response
  • Porites
  • micro-cracking
  • coral geochemistry
  • organic content

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