Wednesday, January 13, 2021

Ocean acidification is transforming California mussel shells


News Release 11-Jan-2021
University of California - San Diego


The large mollusk known as the California mussel makes its home in the rocky shoreline along the Pacific Coast from Mexico to Alaska. Considered a "foundational" animal, Mytilus californianus provides homes for hundreds of other species and offers a rich food source for species ranging from spiny lobsters to humans.

As the waters off our coasts change due to human influences, scientists at the University of California San Diego are finding that the composition of California mussel shells is weakening as it becomes more tolerant of acidic conditions.


Comparing new data with samples collected in the 1950s, UC San Diego Division of Biological Sciences graduate student Elizabeth Bullard and Professor Kaustuv Roy found that ocean acidification is transforming the composition of California mussel shells from mostly the mineral aragonite to the mineral calcite. The results are published in the Proceedings of the National Academy of Sciences.

Aragonite is much stronger than calcite and makes for a better shell to protect against predators and wave energy, two things that are expected to increase with warming waters. Calcite, on the other hand, is much weaker but does not dissolve as easily as aragonite--making a better shell material if the waters are acidifying. Experts had expected aragonite, the stronger of the two substances, to emerge as the dominant mussel shell mineral due to its preference to form in warmer waters. Instead, the new study has shown that the weaker but more stable calcite mineral is now the dominant shell substance, a response linked to increases in ocean water acidity. 

"We found that these mussels are indeed secreting more calcite today than they were 60 years ago," said Bullard. "Lower pH eats away the shells these animals are able to create, so it's considered a major problem for marine organisms. There are 303 species that are associated with the California mussel, so if we lose the mussel we lose other species, some of which are really important to things like our fisheries and recreation."


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