What is ocean acidification, and how does it happen? Oceans act as a sink for carbon dioxide, absorbing 30% of the CO2 released into the atmosphere from burning fossil fuels. Through a series of chemical reactions, an overabundance of CO2 can result in a lower pH, creating a more acidic oceanic environment (the lower the pH of a substance, the more acidic it is). In the last century alone, pH has already decreased by 0.1 units, a notable change in acidity, accompanied by an approximate 1°C increase in ocean temperature. It is no coincidence that the onset of such rapid changes became visible after the Industrial Revolution, considering it initiated the monumental increase in greenhouse gas emissions that continues today.
OA is a relatively new area of study, and the research that has been done thus far has identified varied species-specific responses to increasing acidification that influence reproduction, growth, and behavior. The process of OA reduces the amount of calcium carbonate available for calcifying organisms like plankton, shellfish, and corals, which use calcium carbonate to build their hard parts. Hence, OA directly inhibits their ability to create and maintain protective shells and skeletons.
In studies that looked at the development of marine organisms in conditions of warmer and more acidic waters like those predicted for the year 2100, many showed thinner, weaker, and deformed shells in organisms such as mussels, clams, oysters, and scallops. Many of these organisms are commercially valuable and at the bottom of the food web, supplying food to larger species. If OA undermines populations at the bottom of the food chain, it could result in a trophic cascade: limiting the available prey of larger marine species would potentially reduce predator population sizes, which would then have a corresponding impact on the species that rely on them for food, creating a domino effect all the way up the food chain to the sea’s top predator, humans.
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