Seagrass in San Diego Bay contains 370,000 car-equivalent CO2, port study finds

The amount of carbon in San Diego Bay eelgrass could give scientists insight into the region’s greenhouse gas emissions, a nine-month study showed Monday.

The Port of San Diego conducted a US$150,000 study from the US Department of Transportation Maritime Administration, also known as MARAD, to estimate how much carbon is stored in eelgrass in the bay and how much carbon eelgrass may continue to capture in the future.

According to the study, 2,600 acres of eelgrass in San Diego Bay capture more than 1.7 million metric tons of carbon dioxide, the equivalent of more than 370,000 cars emitted annually. The data was collected between October 2021 and June 2022, and the results were made public on Monday.

“It’s amazing to see what the Port’s environmental efforts have done to bring life back to the Great Bay,” said Rafael Castellanos, Chairman of the Port’s Board of Port Commissioners. “This research and partnership with MARAD and the Navy is part of the port’s holistic approach to combating climate change and helping us achieve our clean air goals.”

Seagrass and other coastal blue carbon ecosystems are able to quickly capture and store large amounts of carbon.

Like all plants, eelgrass absorbs carbon dioxide and releases oxygen. However, unlike land plants, eelgrass is submerged in salt water, which prevents CO2 from being released back into the atmosphere. Carbon lingers in eelgrass plants and soil for thousands of years.

Eeling habitats occupy a small fraction of the area covered by forests on land, but they can store 30 to 50 times more carbon than forests.

The MARAD Marine Environment and Technical Assistance Program was the division of the federal agency responsible for the study.

“In support of the Biden-Harris administration’s ambitious carbon-fighting efforts, the META program supports groundbreaking research to advance decarbonization in the maritime sector,” said Ann Phillips, retired. Rear Admiral and Administrator of the United States Maritime Administration. “MARAD was delighted to be working with the Port of San Diego to explore options for carbon sequestration and looks forward to continuing this innovative effort.”

Since 1993, the port and navy have conducted surveys of eelgrass throughout the bay every few years. San Diego Bay contains 50% of all kelp in Southern California and about 17% of kelp in the state, officials said. Up to 73% of the Bay’s carbon is stored in South Bay sediments.

Over the next year, the port will continue to study the relationship between eelgrass and carbon storage. Under the META program, MARAD provided $175,000 for the second year of research, and a third partner, the US Navy, joined the effort, allowing the team to study carbon sequestration and storage in the Navy’s seagrass recovery areas.

“The port-Navy partnership has greatly benefited the maritime resources in San Diego Bay and the Navy’s conservation program,” said Rear Admiral Brad Rosen, commander of the Navy’s Southwest Region. “The Navy intends to continue to work with the Port and MARAD on this project to further research and manage eelgrass in this vital ecosystem, while successfully balancing the mission of the Department of Defense and sustainable development goals.”

The study is part of the port’s ongoing efforts to protect the resources that the region’s tides provide, as well as to support climate planning efforts.