Quirks & Quarks

Mussels play a shell game to deal with increasingly corrosive ocean waters

California mussels are building their shells from a weaker, but more acid-resistant material to deal with ocean water that is being made more acidic by carbon dioxide emissions.

California mussels are building their shells from a weaker, but more acid-resistant material

Elizabeth Bullard (right) studying mussel shells with a colleague at Corona del Mar, California (Submitted by Elizabeth Bullard)

Warming ocean water and increased ocean acidification have had an impact on the shells of California mussels that make their home along the Pacific coast from Mexico to Alaska. 

Elizabeth Bullard, a PhD candidate in biological sciences at the University of California, San Diego, was part of a team  that found that the composition of mussel shells is weakening as the shellfish adapt to become more tolerant of ocean acidity. 

One of several mussel beds studied along the California coast (Submitted by Elizabeth Bullard)

Baseline study from the 1950's

A new study compared mussel shells collected by a scientist in the 1950's with samples gathered today. The study from nearly 60 years ago showed the composition of mussel shells varied from mussels found in northern cold water to those in southern warmer water.

In cold water, the shells were mostly comprised of the mineral calcite, whereas in warm water they were mostly aragonite. Both are derived from calcium carbonate in sea water.

Aragonite is a stronger material for making shells than calcite, providing better protection against predators and the pounding of waves. Calcite is a weaker material, but itis more resistant to acidic water.

Bleached mussel shells (Submitted by Elizabeth Bullard)

With warming oceans in mind, Bullard and her colleagues assumed aragonite would take over from calcite as the predominant material, but that is not what has happened.

A shell game

This new study found that calcite, even though it is weaker, has become the predominant material. Lower pH levels in acidic waters have reduced shell aragonite in mussels along the Pacific coast. The north-south warm-cold water divide is not the factor it was in the 1950's.

California mussel bed (Submitted by Elizabeth Bullard)

California mussels make their homes along rocky shorelines. They are considered a 'foundational' animal because their presence creates niches for many species and food for many more. 




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