In my last blog, I celebrated emerging efforts to restore native Olympia oysters in San Francisco Bay for their value in mitigating coastal erosion, improving water quality, and other benefits.
But not long after my post went public, scientists from the University of California Davis presented new research showing that Olympia oysters may be facing a challenge that a site-scale restoration project may not be equipped to manage: ocean acidification.
Ocean acidification is often lumped together with climate change, but it has, in fact, no connection with global temperatures at all. What acidification and climate change have in common is that they are both caused by excess CO2 in the atmosphere.
Acidification occurs when CO2 dissolves in seawater and forms carbonic acid, causing a drop in the ocean’s pH levels and a corresponding increase in acidity. Over the last 250 years, average acidity has increased by about 30 percent. Some estimates suggest that – under a business-as-usual scenario in which carbon pollution continues unchecked – the average acidity of the surface ocean could increase by 100 to 150 percent by the end of this century.
What do these changes to ocean chemistry mean for marine life? When carbonic acid levels are high, carbonate ion levels get low, making it difficult for many marine organisms to build their calcium carbonate shells, skeletons, or other hard parts.
Most commercial shellfish use calcium carbonate to build their shells, and UC Davis researchers showed that Olympia oysters are smaller after being exposed, as larvae, to a high carbon-dioxide environment. This finding could spell disaster for oyster aquaculture, which generates more than $100 million in gross sales annually on the West Coast alone, contributing around $273 million overall to the region’s economy. It could also be a serious obstacle for shellfish restoration projects like the San Francisco Bay effort.
Featured photo by: Flickr user The Cozy Shack (A plate of oysters at San Francisco’s Ferry Building. Used under a Creative Commons license.)