FSU Researchers Shed Light On Seaweed's Role In Trapping Blue Carbon

Jun 4, 2019

Shown here in a photo from 2014, sea spaghetti, or the brown alga Himanthalia elongata, dominates the shoreline in July at Cape Cornwall, UK.
Credit Sophie McCoy

Has seaweed been snubbed by science, when it comes to its role in trapping carbon dioxide under the surface of the seafloor? Researchers at Florida State University say seaweed plays a much larger part than most previously thought.

“There’s this pool of carbon called blue carbon that’s been getting a lot of attention,” said Sophie McCoy, a marine biologist and researcher at Florida State University who has been studying the organisms that capture blue carbon, or carbon stored under the seafloor.

The concept of blue carbon is unique to wetlands, and their inhabitants’ ability to trap and store C02 – an essential part of the carbon cycle. But, as McCoy explains, marine plants like mangroves initially got all the credit.

“Maybe a few years ago, people started paying more attention to marine plants, to loosely group them like that, and especially things like seagrasses and mangroves where they have these intricate root systems and they’re very shallow,” McCoy said. “So it’s a more visual process where you can see that they’re trapping their biomass and other sediments.”

Seaweed, or macroalgae, is a productive capturer of C02, but it wasn’t previously thought of as a vehicle for storing it underground.

Kelp detritus, waist-deep, on the beach following autumn storms at Cape Cornwall in October.
Credit Sophie McCoy

“For a long time, the paradigm was that coastal seaweed – it’s really productive and we know that it’s really important for the food web right along the coast,” McCoy said. “But that was sort of what we though their limited role was, spatially.”

So, why is it so important that carbon is kept underground? McCoy says the alternative is to have it return to the atmosphere.

“If you can sequester carbon, like that, outside of the atmosphere, it doesn’t contribute immediately to our global warming,” McCoy explained.

The same process takes place within land plants, McCoy says:

“On earth we know that carbon can be locked up in sort of dead trees and swamps that eventually become petroleum gas products, over time, so that process can also happen in the ocean where they get buried. And over time, become a permanent repository for carbon that’s not contributing to what’s in the atmosphere.”

McCoy says seaweed performs this function after it dies, with help from the microorganisms that eat its dead biomass or “clumps.”

“It’s what they don’t eat that gets stored. But in eating it, they move the sand grains around, and sort of contribute to burying it,” she said.

McCoy adds vast parts of our coastlines are dominated by seaweeds, which means it’s good news the macroalgae can perform its carbon-capturing function:

“Sort of thinking about the different roles that seaweed can have, that can actually turn into ecosystem services that benefit humans – it’s on the rise, and I think that’s a good thing.”

McCoy and the team of researchers found nearly nine grams of carbon are stored per square meter of sediment each year. The research was performed in partnership with Plymouth Marine Laboratory in the United Kingdom. Much of the research was performed off the coast of Plymouth, England.