COS 171-10 - Portuguese oysters produce impaired, mechanically weaker shells at elevated CO2

Friday, August 11, 2017: 11:10 AM
B117, Oregon Convention Center


Yuan Meng, The University of Hong Kong; Zhenbin Guo, The Hong Kong Polytechnic University; Susan Fitzer, University of Glasgow; Vera B. S. Chan, Clemson University; Chaoyi Li, The University of Hong Kong; Abhishek Upadhyay, The University of Hong Kong; Maggie Cusack, University of Glasgow; Haimin Yao, The Hong Kong Polytechnic University; Kelvin Yeung, The University of Hong Kong; V. Thiyagarajan, The University of Hong Kong


Oysters produce calcareous shells to protect them from predation and environmental stressors throughout their life history. After settlement of the free-swimming larvae, oyster juveniles begin to build their calcite shell through a sophisticated biomineralisation process. Decreased pH due to ocean acidification is expected to exert hypercapnia-induced impairment of intracellular pH homeostasis and reduced carbonate ion concentration in the environment, thereby impeding the process of biomineralisation. This study examines the impact of the CO2-induced reduction in pH (ocean acidification) on juvenile shell mechanical strength of the commercially and ecologically important oyster Crassostrea angulata. This study was also the first to combine SEM, micro-CT scanning and nanoindentation analyses to demonstrate the ultimate consequences of reduced calcification in juvenile oysters.


We found that the outermost prismatic shell layer started to deteriorate under a near-future pH 7.8 (control pH 8.1) and was not observed at pH 7.2. The foliated layer with low Mg calcite appears to be highly porous under pH 7.8 to 7.2. The shell hardness and Young’s modulus gradually decreased with decreasing pH, as a consequence of impaired prismatic and foliated layers, shown by nanoindentation. High-resolution micro-computed tomography scanning indicated that the volume ratio of the shell with high mineral density decreased sharply at pH 7.8 confirming the high porosity. This density mapping methodology is commonly used in the biomedical fields such as osteology and dentistry but is relatively new to ocean acidification research. The impact of decreased pH was severe in shells of early juveniles (hinge region) when compared to older juveniles (middle region). Although this oyster species can survive and grow at the projected near future pH of <7.8, the morphologically impaired and mechanically weaker shells with lower density will make them more vulnerable to predators and diseases, therefore threatening the supply of edible oyster resources.