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.
Bibliographical noteFunding Information:
We thank the Earth Observatory of Singapore, Asian School of the Environment, Nanyang Technological University, National Research Foundation Singapore (NRF-RF2012-03), Singapore Ministry of Education, Research Centers of Excellence initiative, and the Marine Science R&D Programme (MSRDP-P03 and MSRDP-P29) for financial and logistical support. Thanks to the Phuket Marine Biological Centre and the National Research Council of Thailand (Proj. ID 2009/043), and the Singapore National Parks (NP/RP16-156-2a). Many thanks to Jeff Oalmann for assistance with the Iolite software, and to Kyle M. Morgan and Riovie Ramos for thoughtful discussions.?This work comprises Earth Observatory of Singapore contribution 347.
© 2021, The Author(s).
- mechanical response
- coral geochemistry
- organic content