The decreasing shell thickness over the past few decades is likely due to ocean acidification.
Mussels that form calcium carbonate shells have undergone significant transformations over the years. New research suggests that modern-day mussels have thinner shells compared to those 50 years ago. This reduced thickness over the past few decades is likely due to ocean acidification as more and more carbon dioxide is penetrating into the oceans. The question arises whether this will affect the shell’s ability to protect mussels under ocean acidification and increasing temperatures.
“The California mussel is a common species along the entire west coast of the United States and their fate will be linked to that of a rich diversity of predators, including sea stars and sea otters, as well as myriad species that are the part of the mussel bed habitat. It is imperative that we understand more about how these species will change as ocean conditions change.” Lead author Cathy Pfister, a professor of ecology and evolution at the University of Chicago said in a statement.
For the latest study, Pfister and her colleagues compared the thickness of modern mussel shells with those collected from the Pacific Ocean off the coast of Washington in the 1970s and shells collected by the local Makah tribe between AD 668 and 1008. On average, shells provided by Makan researchers were almost 27 percent thicker than their modern counterparts. The shells from the 1970s were 32 percent thicker than the modern shells.
“We found that modern shells are thinner overall, thinner per age category and thinner per unit length. Thus, the largest individuals of this species are calcifying less now than in the past.” Authors wrote in the study.
The main driving force behind this long-term decline in shell thickness is ever increasing ocean acidification.
Researchers explain when humans burn fossil fuels, it releases carbon dioxide in the atmosphere and most of this carbon is absorbed by the oceans. This in turn causes pH levels of ocean water to drop and make it more acidic. Many species like mussels and oysters use calcium carbonate for the construction of their shells, but it becomes difficult for these organisms to produce their calcium carbonate shells in such an acidic environment. And this inability will likely make them more vulnerable to predators and environmental changes.
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“Further future decreases in shell thickness could have significant negative impacts M. californianus survival and in turn negatively impact the species-rich complex that occupies mussel bed.”Authors conclude.