Building an integrated coastal ocean acidification monitoring network in the U.S.

Since the beginning of the Industrial Revolution, the release of carbon dioxide (CO2) from industrial and agricultural activities around the world has increased the amount of CO2 in the atmosphere, leading to warming temperatures and changes in weather patterns and climate. However, a significant part of the potential atmospheric CO2 increase has been naturally mitigated as the oceans have absorbed about 30% of all of the CO2 released every year (Feely et al., 2013). This absorption has caused CO2 inventories in the ocean to increase by billions of tons, especially in the last 50 to 100 years (Sabine and Tanhua, 2010). Initially, many scientists focused on the benefits of the ocean removing this greenhouse gas from the atmosphere, until the downside became dramatically obvious in the past few decades (e.g., Feely et al., 2004, 2009; Orr et al., 2005; Fabry et al., 2008; Doney et al., 2009). Observations made by hundreds of scientists at thousands of locations have unambiguously shown that CO2 absorbed by the ocean is changing the fundamental chemistry of the seawater through a process called Ocean Acidification (OA; e.g., Caldeira and Wickett, 2003, 2005; Feely et al., 2009; Mathis et al., 2011). When CO2 is absorbed by seawater, chemical reactions occur that reduce seawater pH and saturation states of biologically important calcium carbonate minerals, such as calcite and aragonite, which are the essential building blocks for the skeletons and shells of many marine organisms. Prior to mankind’s release of CO2 into the environment, most areas of the surface ocean were supersaturated with respect to calcium carbonate minerals. This supersaturation means that there was abundant material for calcifying organisms to build their skeletons and shells. Since then, the pH of surface ocean waters has fallen by an average of 0.1 pH units, which represents a 30% increase in seawater acidity (e.g., Feely et al., 2009; Byrne et al., 2010). Future predictions indicate that if the oceans continue to absorb CO2 based on business-as-usual emission scenarios, they will be 150% more acidic by the end of this century. This scenario would lead to pH levels that the oceans have not experienced for more than 20 million years (Honisch et al., 2012), when CO2 levels were naturally very high in the atmosphere and marine calcifying species such as coral reefs, crabs, and oysters were severely limited in their geographic range or completely non-existent (Portner et al., 2004; Payne and Clapham, 2012). The problem of OA is particularly disconcerting for coastal areas where nearly all ocean-based economic and subsistence activities occur within a few hundred kilometers of shore (Cooley and Doney, 2009). These areas are already under threat from multiple stressors, such as overfishing, pollution, and hypoxia brought on by eutrophication (Portner, 2012; Whittman and Portner, 2013). On a local scale, the combined effects from OA and other natural and anthropogenic processes have already led to failures in hatcheries that rear larval shellfish (e.g., Barton et al., 2012) and caused the degradation and destruction of some planktonic shells (e.g., Bednarsek et al., 2012). While direct organismal impacts have been limited to date, over 1 billion people derive 100% of their protein supply directly from the ocean. Although there is a great deal of variability in organismal responses, even within the same groups, several commercial and subsistence species have shown a low tolerance to OA conditions that are already present at certain times of the year (Kroeker et al., 2013; Whittman and Portner, 2013) and will only worsen in the coming decades. Given the variability in ecosystem responses to OA, there will likely be both winners and losers throughout the marine environment. In the U.S., fisheries from the Bering Sea to the Gulf of Maine are at risk from this potentially looming stressor. There is a critical need for intensive time series measurements and repeat hydrographic cruises in high productivity coastal and estuarine systems, as CO2 and carbonate ion concentrations in these waters can vary substantially on time scales from hours to decades due to tides, photosynthesis, terrestrial inputs, and ocean circulation patterns. Domain Editor-in-Chief Jody W. Deming, University of Washington