Seagrass meadows could play a limited, localized role in alleviating ocean acidification in coastal ecosystems, according to new work led by Carnegie’s David Koweek and including Carnegie’s Ken Caldeira, published in Ecological Applications. Human-induced carbon dioxide emissions are the driving force behind global climate change. This atmospheric carbon dioxide is also absorbed into the ocean where chemical reactions with the seawater produce carbonic acid, which is corrosive to marine life, particularly shellfish that construct their shells and exoskeletons out of calcium carbonate. Seagrasses provide an important source of food and shelter for marine animals, help fight seabed erosion, and filter bacterial pathogens from the water. They also take up carbon dioxide during photosynthesis. Research had demonstrated that California’s coastal estuaries and bays are experiencing ocean acidification. So the team tested the theory that carbon dioxide uptake by seagrass meadows could buffer the pH of local ocean water and help fight short-term effects of acidification. They combined data from seagrass meadows in Tomales Bay, a Marin County, California, inlet, with sophisticated modeling tools that accounted for factors including the amount of seagrass within the meadow, seasonal variation in photosynthetic activity, nighttime respiration, water depth, and tidal currents. “Local stakeholders, such as California’s shellfish industry, want to know whether seagrass meadows may help to counteract ocean acidification,” Koweek said. “Our results suggest that California seagrass meadows will likely offer only limited ability to counteract ocean acidification over long periods.” On average, the computer simulations predicted that the seagrass meadows would turn back the clock on ocean acidification a few decades, a small offset to the more than 150 years of acidification, which is happening more quickly with increasing fossil fuel emissions. However, there were times when their models show that seagrass meadows were able to offer much greater buffering. These happened during periods when low tides occurred during the day, when photosynthesis was active. Koweek and Caldeira say that these offer important opportunities. This level of buffering could make an impact in aquaculture or in natural shellfish communities where marine organisms are able to align their calcification activity with the seagrass buffering periods. “We are starting to understand that some marine organisms, such as blue mussels, are actually able to shift the time of day in which they do most of their calcification. If other organisms are able to do the same, then even brief windows of significant ocean acidification buffering by seagrass meadows may bring substantial benefits to the organisms that live in them,” Koweek said. Koweek and Caldeira are grounded in their optimism for solutions to stop ocean acidification around the world. “Of course, the only way to truly fight ocean acidification is to rapidly and permanently reduce the rate at which we are spewing carbon dioxide emissions into the sky,” Caldeira noted. Koweek added, “However, seagrass meadows are a critical part of California’s coastline. Although our results indicate that seagrass meadows along the California coast are not likely to offer long-term buffering to fight ocean acidification, their enduring role as habitat for marine organisms, protectors against sea-level rise, and magnets of biodiversity should be more than enough reason to restore and protect these iconic ecosystems.”  SUPPORT AND COLLABORATORS: The paper’s other coauthors are Richard Zimmerman of Old Dominion University; Kathryn Hewett, Brian Gaylord, and John. J. Stachowicz of University of California, Davis; Sarah Giddings of University of California, San Diego’s Scripps Institution of Oceanography; Kerry Nickols of California State University, Northridge; Jennifer Ruesink of University of Washington; and Yuichiro Takeshita of the Monterey Bay Aquarium Research Institute. This work is a contribution of the Seagrass Ocean Acidification Amelioration Workshop of the Bodega Marine Laboratory, financial support for which was provided by California Sea Grant and the Coastal & Marine Sciences Institute of the University of California, Davis. The National Science Foundation provided partial support. Can Seagrass Help Fight Ocean Acidification? This is a seagrass bed off the California Channel Islands. Such beds are important for marine life food and shelter. They also help fight seabed erosion, filter pathogens from the water, and absorb carbon dioxide during photosynthesis. Image courtesy Claire Fackler, Channel Islands National Marine Sanctuary, NOAA Atmospheric carbon dioxide is absorbed into the ocean where chemical reactions with the seawater produce carbonic acid, which is corrosive to marine life. Image courtesy NOAA Carnegie postdoctoral researcher David Koweek was lead author on the study. Image courtesy David Koweek 14