Study shows seagrass helps mitigate rates of ocean acidification


A recent study conducted by the Carnegie Institution of Science based on data from Tomales Bay indicates that seagrass has an important role to play in curtailing the rate of ocean acidification. Eelgrass, which is a type of seagrass, has already been shown to reduce erosion rates and provide habitat for crabs and fish. “Interestingly, we actually never had to go into Tomales Bay to collect the seagrass to conduct the experiment,” explained David Koweek, the lead author of the study. “Computer models allow you to ask questions in a really non-invasive way. They’re also really efficient. Simulating a month of data took a minute on my laptop.” The study was able to draw on the deep pool of available knowledge about Tomales Bay to set water conditions based on the season, light levels, depth and tides. “The question is whether or not marine plants—not just seagrass, but also kelp—can buffer water,” Dr. Koweek said. “The model is tailored to Tomales Bay, but we can think of the results as really broadly applicable to estuaries in California, Oregon and Washington.” Ocean acidity has increased by 30 percent since the start of the Industrial Revolution, and current forecasts expect it to double compared to pre-industrial levels by 2100. The rise in acidity has particularly grave implications for shellfish, whose calcium carbonate shells dissolve in acidic water. “We are starting to see evidence of the impact of ocean acidification along the California coast,” Dr. Koweek said. “In particular, some of the shellfish operations in Oregon and Washington have experienced failure that they have attributed to ocean acidification.” Tomales Bay, which is home to several oyster and clam operations, is at risk of similar challenges. The restoration of seagrass could help temper the rate of acidification through photosynthesis: marine plants decrease water acidity by removing carbon dioxide from water in their respiration process to make sugars. Recent studies estimate that Tomales Bay have about 23 percent seagrass coverage, although grasses in the west side of the bay have been threatened by extensive water runoff after heavy rains, which lower salinity levels. “Eventually it will come back,” said study coauthor Jay Stachwitz. “The study is adding yet another benefit to seagrass. It also provides this potential benefit to reduced acidification on a very local scale.” Research indicates that seagrass meadows are most productive in shallow water with lots of light, where water moves through relatively slowly. Dr. Koweek hopes the results incentivize decision-makers along the coast to prioritize seagrass meadow restoration. But, he said, “part of making smart decisions is understanding the potential of seagrass meadows but also understanding their limitations. It’s not going to be this silver bullet that solves all of our problems along the California coastline.”