Oysters on the Thin-Shell: Signs of Ocean Acidification

Written by Sarah G. Newkirk on . Posted in Learn

Editor’s Note: Today Planet Change features another post from the California Climate Change Chronicles, or C4, a periodic blog providing a California perspective on climate change policy and innovation. Sarah Newkirk helps us understand how our oceans are changing and what it means for a favorite delicacy.

In my last blog on this site, 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.

Not all of the organisms at risk of ocean acidification  are as well-known as oysters.  Take pteropods – or “sea butterflies” – for example. You might not have heard of these critters, but they are a critical food item for marine fisheries,such as salmon, that are not otherwise vulnerable to acidification of the oceans.  Research indicates that – when exposed to ocean water with the acidity that is projected for the year 2100 – the shells of pteropods literally dissolve within 45 days.  We are only just beginning to understand these larger ecosystem-scale impacts of acidification.

Atmospheric CO2 emissions are not the only source of ocean acidification; other human activities can compound the problem. For example, people’s activities on land – such as the use of fertilizer, and municipal and industrial wastewater production – can create runoff that causes algae to bloom in marine waters. When the bloom ends, the dying algal material sinks into deeper water and decays, consuming oxygen and releasing large amounts of carbon dioxide into the water.  The carbon dioxide released from this process of growth and decay has the same acidifying effect as carbon dioxide absorbed into seawater from the atmosphere.

Some amount of ocean acidification is inevitable – we’ve already emitted enough CO2 into the atmosphere to cause significant changes to ocean chemistry.  That is not a reason for inaction, however – the sooner we act to stem the sources of acidification, the more limited its impacts will be and the better we will be able to protect our shellfish industry and marine ecological systems. 

At least one state is not waiting to act. Late last year, Washington Gov. Chris Gregoire, announced the first major state-level effort to protect valuable shellfish industries and marine life from the impacts of ocean acidification.  Responding to a report by the State Blue Ribbon Panel she commissioned, Gov. Gregoire directed state agencies to take steps to reduce pollutants that contribute to acidification. 

The report includes 42 recommendations for state action, including reducing CO2 emissions, reducing land-based contributions to acidification, and increasing our ability to adapt to,  monitor and document  its impacts. These recommendations are equally applicable to other states (hint hint, California). 

Sarah G. Newkirk is Coastal Project Director for The Nature Conservancy in California.

Visit The Nature Conservancy’s California Climate Change Program to learn more about innovative nature-based solutions to limit the severity of climate change.

Featured photo by: Flickr user The Cozy Shack (A plate of oysters at San Francisco's Ferry Building. Used under a Creative Commons license.)

Photo 2 by: Flickr user GrooveSurfer (Washington oysters on display in San Francisco. Used under a Creative Commons license.)

Photo 3 by: Matt Wilson/Jay Clark, NOAA NMFS AFSC, Flickr user NOAA Photo Library (Zooplankton including “Octopus” and pteropod on right. Used under a Creative Commons license.)

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Planet Change is a Nature Conservancy blog site designed to share stories about actions the Conservancy and others around the world are taking to fight carbon pollution and the impacts of climate change, and to help people feel the connections between climate change and their daily lives and understand actions they can take.

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