Introduction & Background
Human-driven climate change involves the build-up of excess CO2 in the Earth’s atmosphere
due to the burning of fossil fuels and land use change. The ocean absorbs up to 30% of these emissions, causing a series of chemical reactions that increase the concentration of hydrogen ions. This causes the ocean to become acidic due to the relatively low concentration of carbonate ions, also known as ocean acidification (OA) [1].
Carbonate ions are crucial in marine structures such as corals and shells of calcifying organisms. Calcifying organisms are species that form shells made of calcium carbonate such as mollusks, echinoderms, crustaceans and certain types of phytoplankton. The process of creating these exoskeletons is called calcification [2].
In the past, ocean pH has varied by small amounts naturally. Still, those effects are not worrying nor of interest to researchers as they do not resemble the current crisis due to climate change in which pH is varying by large amounts that organisms cannot adapt to [3].
Due to OA and climate change, mollusks are rapidly losing their ability to create exoskeletons and function in a marine ecosystem. This loss of mollusks will have a devastating impact on human systems. Mollusks such as clams, oysters and octopuses are commonly eaten in places like China and France. In 2005, China accounted for 80% of the global mollusk catch, netting almost 11 million tonnes [4]. Hence, mollusks are a vital part of the food that humans eat as well as a large portion of the economy in various countries. The eventual disappearance of mollusks will have devastating impacts on different industries.
Therefore, let us review some of the most prominent studies within this field and their
significance. This can provide information on how to prevent these impacts or persuade others to change their behavior to prevent further damage.
Literature Review
The first study to model the effects of ocean acidification (OA) on coral reefs appeared in 1999 by Gattuso et al. This study created metadata models by compiling four datasets on temperate coralline algae, two datasets on Scleractinia corals and one on a coral reef community. Six of the seven datasets showed a decrease in the rate of calcification in the studied groups over the acidic pH range of 0-6.2.
Gattuso et al.’s study went unrecognized for a long time until there was a landmark study done by Scott Doney that outlined all possible effects of OA and how they are destroying marine ecosystems. This study, published in 2007, reviewed scientific evidence to compile a manuscript about the effect OA already has on the Earth’s marine ecosystems, specifically coral reefs.
Doney highlighted that previous laboratory experiments find that calcification and growth rates of coral reefs are significantly reduced under high-CO2 conditions [5].
Doney’s study was the study that triggered large amounts of research into this field. Before this time, climate change was not regarded as a large threat and hence its effects were largely disregarded. One of these studies very briefly investigated the effects of OA on marine life, rather than just coral reefs. The study, once again a literature review by Doney, found that though marine animals may find a way to adapt to rising CO2 levels in the ocean, it may come at a higher metabolic rate. One of the few sentences Doney writes about marine organisms is, “In sea urchin larvae, elevated CO2 alters gene expression and may reduce tolerance to other environmental stresses” [3].
It is still apparent that the understanding of the effect of OA on marine organisms is
underdeveloped. Doney even found in his study that there was no information on how marine organisms will adapt to increasing CO2 levels [2].
However, with new information coming to light, researchers were able to find new methods of studying OA. Buddemeier et al. developed a spreadsheet-based numerical model that uses equations developed from data on coral growth and mortality rates. The model calculates the impacts on coral covers as the ocean acidifies. This model is used to compare past environmental history with predictions [3].
While Buddemeier’s study provided insights into marine ecosystems, the most effective studies are those done in laboratories. Perera et al. mimicked acidified ocean water with acidic buffer solutions of varying pH. They then used calcite pieces to represent calcifying organisms and their shells. This study provided the understanding that as the pH decreases (ocean gets more acidic), the percent of mass loss of the calcite increases exponentially [6].
It is important to note that this is one of the very few reliable studies done on OA in the
laboratory, hence showing a clear gap in the field. As has been shown, most of the research
focuses on OA’s effect on coral reefs and there is almost no mention of mollusks in any reliable sources. There must be research into the effects of OA on mollusks as these are the marine species that humans interact with the most. There also must be more laboratory experiments rather than reliance on theoretical models as models can only predict accurately to a limited extent [7].
Conclusion
In conclusion, there is significant value in researching the effect of ocean acidification on the
exoskeleton of mollusks. By reviewing various literature done in the field, a clear gap was
identified as current research only focuses on coral reef structures.
Hence, through extensive research and evidence presented throughout the proposal, the
hypothesis is that there will be negative effects on mollusks and their shells. Research into this field will provide invaluable insight into climate change and its effects and what must be done to mitigate these effects.
Climate change is an ever-changing field that is not completely understood even to this day. In order to save the planet and its organisms, research into this field should be encouraged.
The Author
Akriti Sharma (she/her) is a second year student at the University of Toronto, currently majoring in Mechanical Engineering. She enjoys focusing on biomedical sciences and engineering in her academic pursuits.
Bibliography
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