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Blue Carbon: Could eelgrass help save the Bay?

Research Associate Mike Doan loves to explore eelgrass meadows from above and below the water.

When you ask people if they have a favorite sea creature, they may name a winsome harbor seal or an imposing great white shark. If you ask that question of Mike Doan, Friends of Casco Bay’s Research Associate, he’ll say, “Eelgrass.”


Mike says, “Eelgrass beds are Casco Bay’s rainforest. They are one of the most productive and biologically diverse habitats on the planet. When I am diving or drifting over an eelgrass meadow, it just makes me feel relaxed and peaceful.”

Mike is not alone in his appreciation of this exceptional plant. It is one of the few true marine flowering plants, with roots, stems, and leaves. Many sea creatures look to eelgrass for foraging, hiding places, and something to grab on to in the shifting tides of the estuary. The long, flowing leaves dampen wave action, and the roots anchor the mud, inhibiting shoreline erosion.

Now some scientists, including Mike, suspect that eelgrass beds may provide an even bigger benefit to the marine ecosystem: perhaps eelgrass can help temper the effects of acidifying seawater. Coastal acidification is caused by the increase in carbon dioxide (CO2 ), both from the absorption of CO2 released into the atmosphere by burning fossil fuels and from nitrogen flushed into the ocean by rainwater runoff.

Because eelgrass extracts huge amounts of nitrogen and carbon from seawater, eelgrass may well have a role in mitigating coastal acidification. A new area of research termed Blue Carbon is investigating the way that sea grasses, salt marshes, and mangroves take up and hold carbon in the tissues of the plants. Much of that carbon is transferred into the sediments, “sequestering” the carbon from circulation for many years. Scientists have found that sea grasses and salt marshes absorb and hold up to ten times more carbon than forests on land.

Seaweeds such as kelp also take up nitrogen and carbon. How can they be helpful? Mike says that if we promote seaweed aquaculture, we can later harvest the plants, effectively taking away the carbon and nitrogen they absorb from coastal waters. “Cultivating and cutting algae for biofuel or for food would help remove excess nitrogen and carbon dioxide from the ocean, which in turn would help neutralize the water chemistry to nurture the growth of shellfish such as clams and mussels.”

[box] Coding carbon by color What is Blue Carbon? The National Oceanic and Atmospheric Administration defines blue carbon as the fraction of carbon taken up and stored in ocean and coastal ecosystems, such as mangroves, sea grasses, and salt marshes. Green carbon is the carbon that is taken up by terrestrial ecosystems, such as forests and fields. Black carbon is the carbon that’s released in the production and burning of coal, oil, and gas.[/box]