Seaweeds and seagrasses have potential to mitigate some effects of ocean acidification, according to a new report presented to the California state legislature earlier this month. The report was supported by the Ocean Protection Council. California Sea Grant Extension Specialist Joe Tyburczy, who is based at Humboldt State University, served on the working group that wrote the report.
“The major take-home message in the report is that seagrass and kelp may be quite beneficial for reducing the impacts of ocean acidification, especially in California’s bays,” Tyburczy says. While many details remain to be studied, the researchers say that restoring or preserving seagrass and kelp is a win-win measure that would also bring a number of other benefits. For example, seagrass meadows are important habitat for many marine species, including economically important fisheries like crab. Kelp and seagrasses can also moderate wave impacts, protecting coastlines from storms.
“There are many reasons we’d want to restore or preserve seagrass meadows. The potential of seagrasses to remove carbon from the water is just icing on the cake,” says University of California, Davis scientist Tessa Hill, who has conducted related research on the topic.
With its long coastline, California has a front-row seat to many of the first impacts of climate change: rising sea level, changing weather patterns, and increased water temperatures are already having visible effects on the state.
Another impact that is not yet so visible—but potentially just as damaging to both the environment and the economy—is ocean acidification. As levels of carbon dioxide (CO2), the principal gas driving climate change, increase in the atmosphere, some of it dissolves into the ocean, leading to higher levels of CO2 in seawater. The oceans may not be fizzing like a carbonated soda, but dissolved CO2 makes water more acidic, which makes it more difficult for animals like mussels and oysters to build and maintain their calcium-carbonate based shells. Ocean acidification is already impacting oyster hatcheries and could become a major problem for oyster and abalone farmers, as well as for wild shellfish populations; even if CO2 emissions ceased tomorrow, ocean acidification on the West Coast will intensify for at least 30 to 50 years because of the increasingly acidic water already loaded into the ‘pipeline’ of deep ocean currents.
The idea that seagrasses could help mitigate ocean acidification stems from their basic biochemistry: like green plants on land, seagrasses and kelp use sunlight to turn CO2 and water into plant matter. Through the process of photosynthesis, seagrass and kelp take up carbon from the water and convert it into new vegetation; some of this may decompose into organic carbon in sediment where it ceases to contribute to ocean acidification and climate change.
In her California Sea Grant-funded research in Tomales Bay, California, Hill showed that sediment inside seagrass meadows can contain up to two times as much organic carbon as habitats without vegetation. She also found that in summer months, the presence of seagrass can make water significantly less acidic, changing water chemistry up to 0.1 pH units.
The results of the project were so promising that they led to a larger project to expand the research across the state, and also compare seagrass meadows that were restored rather than native.
The idea of a nature-based solution with multiple benefits sounded good to policymakers who are working on strategies to address ocean acidification. The question will be when, where, and how to prioritize seagrass restoration and protection. That’s where current research aims to fill the gaps.
She says, “We’re trying to develop a list of the characteristics of seagrass meadows that are better at sequestering carbon, at buffering acidic water. If we can identify the characteristics that would maximize their capability, we could strategically work to conserve or restore seagrass or kelp beds with that in mind.”
Tyburczy, who lives and works in Humboldt, has been investigating the potential of eelgrass (a native seagrass species) to buffer ocean acidification in Humboldt Bay through a project funded by the California Ocean Protection Council. He says, “There are big questions about how much seagrasses and seaweed alter water chemistry and how effective they may be. The biomass and physiological status of kelp and eelgrass, amount of light, amount of water, and how quickly the water is moving are all major factors.”
Insight for decision makers
In addition to the science team that presented the report in Sacramento, lawmakers also heard from Hill and researchers at the Nature Conservancy and California State University Northridge on research and actions being taken locally.
Hill says, “California is at a moment in time where we are showing leadership on how to both address climate change and also help communities adapt to climate change. Our state government has been very innovative in this respect, and has asked for scientific research that will help them make decisions on that pathway.” Indeed, this report was prepared in response to Senate Bill 1363 (Monning) which was passed by the California legislature in 2016 and called for the Ocean Protection Council to explore the potential for protection and restoration of eelgrass and other habitats to reduce the impacts of ocean acidification on the state.
“The report and committee hearing were helpful in revealing to policymakers how aquatic vegetation management – particularly eelgrass – can help coastal communities adapt to the inevitable of climate change. Because of this information, I have a better understanding on how eelgrass can be used to mitigate ocean acidification and help preserve coastal habitats,” says Assemblymember Mark Stone, who represents California’s 29th district, located on the central coast.