Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 22
Biogeosciences, 15, 6833-6846, 2018
https://doi.org/10.5194/bg-15-6833-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 6833-6846, 2018
https://doi.org/10.5194/bg-15-6833-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 16 Nov 2018

Research article | 16 Nov 2018

Ocean acidification reduces hardness and stiffness of the Portuguese oyster shell with impaired microstructure: a hierarchical analysis

Yuan Meng1, Zhenbin Guo2, Susan C. Fitzer3, Abhishek Upadhyay1, Vera B. S. Chan4,5, Chaoyi Li1, Maggie Cusack6, Haimin Yao2, Kelvin W. K. Yeung7, and Vengatesen Thiyagarajan1,8 Yuan Meng et al.
  • 1The Swire Institute of Marine Sciences and School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
  • 2Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China
  • 3Institute of Aquaculture, Faculty of Natural Sciences, University of Stirling, Pathfoot Building, Stirling, FK9 4LA, UK
  • 4Department of Biological Sciences, Clemson University, Clemson, SC, USA
  • 5Physiologie Fonctionnelle des Organismes Marins UMR 6539 LEMAR (CNRS/UBO/IRD/Ifremer), Ifremer, CS 10070, 29280, Plouzané, France
  • 6Division of Biological & Environmental Sciences, Faculty of Natural Sciences, University of Stirling, Cottrell Building, Stirling, FK9 4LA, UK
  • 7Department of Orthopaedics and Traumatology, Queen Mary Hospital, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
  • 8State Key Laboratory for Marine Pollution, Hong Kong SAR, China

Abstract. The rapidly intensifying process of ocean acidification (OA) due to anthropogenic CO2 is not only depleting carbonate ions necessary for calcification but also causing acidosis and disrupting internal pH homeostasis in several marine organisms. These negative consequences of OA on marine calcifiers, i.e. oyster species, have been very well documented in recent studies; however, the consequences of reduced or impaired calcification on the end-product, shells or skeletons, still remain one of the major research gaps. Shells produced by marine organisms under OA are expected to show signs of dissolution, disorganized microstructure and reduced mechanical properties. To bridge this knowledge gap and to test the above hypothesis, we investigated the effect of OA on juvenile shells of the commercially important oyster species, Magallana angulata, at ecologically and climatically relevant OA levels (using pH 8.1, 7.8, 7.5, 7.2). In lower pH conditions, a drop of shell hardness and stiffness was revealed by nanoindentation tests, while an evident porous internal microstructure was detected by scanning electron microscopy. Crystallographic orientation, on the other hand, showed no significant difference with decreasing pH using electron back-scattered diffraction (EBSD). These results indicate the porous internal microstructure may be the cause of the reduction in shell hardness and stiffness. The overall decrease of shell density observed from micro-computed tomography analysis indicates the porous internal microstructure may run through the shell, thus inevitably limiting the effectiveness of the shell's defensive function. This study shows the potential deterioration of oyster shells induced by OA, especially in their early life stage. This knowledge is critical to estimate the survival and production of edible oysters in the future ocean.

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The paper revealed a potential structural deterioration induced by ocean acidification on the shells of an ecologically and economically important oyster, which is critical to forecasting the survival and production of edible oysters in the future ocean. Importantly, this is a multidisciplinary collaboration including aquaculture, crystallography, medical and materials science, which could be applied to other biomineral systems to hierarchically analyse the impact of ocean acidification.
The paper revealed a potential structural deterioration induced by ocean acidification on the...
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