Marine Life Can Resist Ocean Acidification by Modifying Shell-Building Process at the Nanoscale

Significance 

Some of the most important and diverse animals in the ocean are shell-builders, which produce calcareous shells for both growth and protection. Therefore, the process of shell production (i.e. calcification) is fundamental to maintaining their populations and hence functioning of marine ecosystems. However, with the ocean becoming more acidic due to ever-increasing carbon dioxide (CO2) emissions, the fitness and survival of shell-builders in the future have raised concerns. Based on the results of laboratory-based research, ocean acidification has been shown to reduce their shell-building capacity, weaken the mechanical strength of their shells, or hinder their population growth and survival. Nevertheless, growing evidence from the natural environments reveals that some shell-builders appear to be capable of resisting the “corrosive” effect of acidified seawater on their shells. Understanding how they can maintain their shell-building capacity in the future acidifying ocean becomes increasingly important in marine research.

Calcareous shells are primarily made up of calcium carbonate minerals and typically arranged in hierarchical structures. Unlike manufactured materials with known mechanical strength, the mechanical strength of calcareous shells can vary, subject possibly to the atomic arrangement of the calcium carbonate crystals – the building blocks. As such, the mechanical strength may be determined by the thickness and package of the carbonate crystals as well as how their nanoscale arrangements adjust to the changing environmental conditions. It is worth noting that the effects of ocean acidification also depend on the ecological and evolutionary processes that influence the adaptive mechanisms initiated by shell-builders to modify their shell-building process and leverage on the short-term negative effects. The adaptive mechanisms include adjusting the shell structural properties and packing of the calcium carbonate crystals to build durable shells.

Herein, the researchers in the University of Adelaide, Australia: Dr. Jonathan Leung, Dr. Yujie Chen, Prof. Ivan Nagelkerken, Prof. Zonghan Xie and Prof. Sean Connell, in collaboration with Prof. Sam Zhang from Southwest University, studied the response of the abundant calcifying marine snails (Eatoniella mortoni) to ocean acidification and whether they can adaptively modify their shell structural properties. This particular snail is ideal for the research objective because of its ability to inhabit natural CO2-acidified environments for multiple generations. The work is published in the research journal, Small.

In their approach, the natural CO2 vents at the western Pacific were utilized. To test for any limits of structural plasticity (i.e. adaptive modifications of shell structures) to acidified seawater, the marine snails were collected across the pH gradients that represent the contemporary conditions (pH 8.1), predicted future conditions in the year 2100 (pH 7.8) and extremely acidified environment (pH 6.6). The researchers correlated the shell properties, including porosity, nanotwin thickness and organic matter content, with mechanical performance to evaluate the adjustability of the marine snails to ocean acidification.

Results showed that the marine snails were able to adaptively modify the building block of their shells to build mechanically stronger and more resilient shells under the predicted future conditions, compared to contemporary conditions. The shells were characterized by increased resistance to fracture, which was associated with reduced porosity, reduced nanotwin thickness and increased organic matter content. However, the shells became more fragile with increased porosity in the extremely acidified environment, probably attributed to the excessive corrosion by the highly acidified seawater.

In summary, the authors are the first to report the nanoscale adjustments of shell structures as part of the adaptive mechanisms exhibited by shell-builders to maintain the mechanical performance of their shells under near-future ocean acidification. The results provided critical insights into why some shell-builders may thrive in natural CO2-acidified environments. Nevertheless, the adaptive capacity of the snails had a limit as they failed to build durable and mechanically resilient shells under extreme levels of acidification. With continuous human-caused environmental changes, the information provided in this study would advance research on the adaptive responses among other shell-builders, such as corals, mussels, oysters and sea urchins. Particularly, authors explained their findings would pave the way for further understanding of the molecular adaptation of marine animals to the future acidifying ocean.

Marine Life Can Resist Ocean Acidification by Modifying Shell-Building Process at the Nanoscale - Advances in Engineering

About the author

Jonathan Y.S. Leung received his PhD degree from the University of Adelaide, Australia in 2018 and was awarded Dean’s Commendation for Doctoral Thesis Excellence. He currently works as a postdoctoral research fellow at Southwest University in China in collaboration with the University of Adelaide. His recent research focuses on how ocean acidification and warming affect the fitness and survival of marine organisms as well as their adaptation from the perspectives of physiology, geochemistry and materials science. Apart from marine biology, he is also interested in environmental chemistry to understand how anthropogenic pollutants, such as heavy metals, persistent organic pollutants and microplastics, impact human and ecosystem health.

Email: [email protected]

About the author

Yujie Chen obtained her BEng degree (first class honours) in 2011 and PhD degree in Materials Science in 2016 from the University of Sydney. Upon completion of her PhD degree, she was employed as a postdoctoral research fellow in the School of Mechanical Engineering at the University of Adelaide in Australia. She is currently a postdoctoral research fellow at Southwest University in China. Her current research involves microstructure optimization and mechanical properties enhancement of alloys and calcified tissues.

Email: [email protected]

About the author

Ivan Nagelkerken is a professor in marine ecology working in temperate and tropical coastal ecosystems, with a special focus on fishes. Over the past decade, he has examined how ecosystem connectivity affects the functioning and resilience of tropical coastal ecosystems, including coral reefs, seagrasses and mangroves. Most of this work has been conducted in the Caribbean, Eastern Africa and Australia. He held a Future Fellowship awarded by the Australian Research Council to study the effects of climate change on fishes and marine ecosystems, and he currently continues to work on this research field.

Most of his climate change research is performed in Australia and New Zealand. His work contributes directly to today’s environmental issues by providing answers to contemporary scientific questions as well as management and conservation related problems.

Email: [email protected]

About the author

Zonghan Xie is a professor in the School of Materials Science and Surface Engineering at the University of Adelaide, Australia. He received his PhD degree in Ceramic Engineering from the University of New South Wales, Australia in 2004. In the same year, he was awarded the Australian Postdoctoral Fellowship and conducted research on engineering coatings. Later, he worked as a research fellow at the University of Sydney and the Centre for Integrated Nanotechnologies of the Los Alamos National Laboratory (NM, USA) before returning to Australia in 2008 to establish and lead a materials research group at a regional university in Western Australia. He joined the University of Adelaide in 2012. His current research involves metallurgical coatings, high-strength alloys and calcified tissues.

Email: [email protected]

About the author

Professor Sam Zhang (FRSC, FTFS, FIoMMM) earned his PhD degree in Ceramics in 1991 from the University of Wisconsin-Madison, USA. He was a tenured full professor at Nanyang Technological University, Singapore. In January 2018, he joined the School of Materials and Energy at Southwest University in China. He is the founder and director of the Centre for Advanced Thin Films and Devices at Southwest University (http://fmae.swu.edu.cn/s/fmaenew/yjzx/).

His research includes energy films and coatings, biological materials and hard coatings. He has published 13 books and over 360 peer-reviewed international journal papers (h-index: 54 as at April 2021; https://publons.com/researcher/2817766/sam-zhang/). His book “Materials Characterization Techniques” has been adopted by more than 30 American and European universities as a core textbook. His two new books “Protective Thin Coatings” (CRC: 380678) and “Functional Thin Films” (CRC: 380678) are currently in press at CRC Press.

Email: [email protected]

About the author

Sean D. Connell is a professor in the School of Biological Sciences at the University of Adelaide. He received his PhD degree from the University of Sydney. As a biologist, his work involves testing biological responses to environmental change at nano-scales through to continental-scales. His work has led to improved government policies that restore coastal water quality and restore extinct ecosystems. This work has been recognised by Queen Elizabeth II Fellowship and Future Fellowship (Australian Research Council) and national awards.

Email: [email protected]

Reference

Leung, J., Chen, Y., Nagelkerken, I., Zhang, S., Xie, Z., & Connell, S. (2020). Calcifiers can Adjust Shell Building at the Nanoscale to Resist Ocean AcidificationSmall, 16(37), 2003186.

Go To Small

Check Also

Jubilee Church in Rome-Advances in Engineering

Building defects in new iconic structures