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Ocean acidification altering the architecture of California mussel shells

"What we've seen in more recent shells is that the crystals are small and disoriented," said researcher Sophie McCoy.

By Brooks Hays
Ocean acidification altering the architecture of California mussel shells
Ocean acidification is altering the predictable patterns of mineralogy found in the shells of the California mussel. Photo by Sophie McCoy/FSU

Jan. 5 (UPI) -- California mussels aren't built like they used to be. According to new research, increasing ocean acidification is altering the structural makeup of mussel shells along the West Coast.

Traditionally, long, cylindrical calcite crystals for neat and predictable rows in the shells of California mussels, Mytilus californianus. But as detailed in a new study, published in the journal Global Change Biology, that geometric consistency is no more.

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"What we've seen in more recent shells is that the crystals are small and disoriented," study leader Sophie McCoy, assistant professor of biological science at Florida State University, said in a news release. "These are significant changes in how these animals produce their shells that can be tied to a shifting ocean chemistry."

Scientists at MSU analyzed the mineralogical composition of California mussel samples from Tatoosh Island off the coast of northern Washington. They compared the mussels to shells from the 1970s, as well as to mussel fossils dated to several thousand years ago.

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Their analysis showed composition has remained constant for thousands of years, but has become more irregular over the last 15 years.

"When the mussels are ready to build their shells, they first lay down an amorphous soup of calcium carbonate, which they later order and organize," McCoy said. "More recent shells have just started heaping that calcium carbonate soup where it needs to go and then leaving it there disordered."

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Chemical analysis also showed modern mussel shells feature increasing amounts of magnesium, suggesting the formation process has been significantly altered by the ocean's changing acidity. Heightened magnesium levels are responsible for the variability of the shells' mineralogy.

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Many studies have suggested rising global ocean temperatures, acidification and oxygen loss will deplete biodiversity, and researchers suggest in this instance variability could prove beneficial to the mussel.

"An important theme of climate change science is that increased variability might be the new rule," McCoy said. "We know that climate change right now is happening faster than what the Earth has experienced before, but we also see that over these long timescales, things tend to plateau and stabilize. Variability is the basis of natural selection, and the fact that we now see so much variability in the mussels' individual traits means there is potential for natural selection to act."

While there may be fewer mussel species and smaller populations, McCoy thinks at least some will prove resilient enough to survive, adapt and thrive.

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"I don't know if this species will succeed in the future, but I have too much confidence in the natural processes of ecology and evolution to think that we'll have barren oceans," she said.

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