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Study on shellfish response to ocean acidification

By Tim Stephens

Studying effects of ocean acidification on West Coast mussels

Integrative Biology professors Francis Chan and Bruce Menge and recent integrative biology graduate Jeremy Rose (PhD '15) are co-authors of a study on the effects of ocean acidification on West Coast mussels published in Ecology Letters.

The study examined how juvenile mussels respond to varying environmental conditions at seven sites spread across 800 miles of coastline in California and Oregon. The results showed that the ability of mussels to cope with more acidic conditions depends largely on how much food is available to them, and both factors vary from place to place in a complex geographic mosaic of environmental and ecological conditions.

Ocean acidification

As the oceans absorb increasing amounts of carbon dioxide from the atmosphere, ocean acidification is expected to make life harder for many marine organisms, especially shellfish and other animals with shells or skeletons made of calcium carbonate. Acidification refers to a lowering of the pH of seawater when it absorbs carbon dioxide, pushing it closer to the acidic end of the scale, although it is still slightly alkaline. A small decrease in pH affects the chemical equilibrium of seawater, making it harder for organisms to build calcium carbonate structures.

oysters sitting in small creek

Mussels finding it harder to sustain with ocean acidification

For mussels, that can mean thinner shells, making them more vulnerable to predators like the dogwhelk, a marine snail that attacks mussels by drilling through their shells. The lower the pH, the more energy it takes to build a shell, so the food supply is crucial in determining how well mussels can cope with ocean acidification.

The team took advantage of geographic variability in the wind-driven upwelling of cold, deep ocean water along the West Coast. That deep water is not only rich in nutrients, it also has relatively high concentrations of carbon dioxide, both because it is cold (cold water can absorb and hold more carbon dioxide than warm water) and because the decomposition of organic matter that sinks into the depths releases carbon dioxide. Ocean acidification is further increasing the acidity of that deep water.

This work was funded by the National Science Foundation, University of California, and the David and Lucile Packard Foundation.

The complete article can be found online.