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Seagrass in BC waters store far less 'blue carbon' than similar sites worldwide

June 13, 2018
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Seagrass meadows on the west coast of Vancouver Island store substantially less carbon than seagrass sites in other parts of the world, according to a new study by SFU and Parks Canada researchers.

Seagrasses use photosynthesis to draw carbon dioxide out of the atmosphere and store it in their leaves, roots and the sediment below them. Because of their ability to store this ‘blue carbon,’ seagrass meadows have been touted as an important way to combat climate change.

But critics argue that seagrass blue carbon may be dramatically overestimated in northern systems, and may not store as much carbon as once thought.

In the summer of 2016, a team of researchers from SFU and Parks Canada were funded by the Commission for Environmental Cooperation to get the first measurements of how much blue carbon is stored in seagrasses in Pacific Rim National Park Reserve and Clayoquot Sound.

An SFU team, led by resource and environmental management master’s students Victoria Postlethwaite and Aimee McGowan, worked cooperatively with Parks Canada scientists and found more carbon was stored in the seagrasses than in the bare patches of muddy sediments nearby. But the numbers were still a lot lower than found in tropical and sub tropical systems. In fact, the amount of carbon stored in Clayoquot Sound (both in total and each year) is less than a 10th of what’s thought to be stored in many other places around the globe.

The SFU students believe the difference is driven by many reasons, including the species of seagrass, the low light conditions in BC, temperatures, nutrients, and water conditions.

“There are many other reasons to conserve seagrass meadows,” says Postlethwaite, lead author on the paper, “for one, because they provide crucial habitat for fish.

“But this study shows that, in terms of climate change mitigation, there should be a move away from assumptions that carbon stores are similar on a global basis, and instead a focus on getting an accurate regional picture.”

Their study, entitled Low blue carbon storage in eelgrass (Zostera marina) meadows on the Pacific coast of Canada was published Wednesday in the journal PLOS ONE.

Fast Facts:

-     Eelgrasses provide a multitude of ecosystem benefits, such as fish/spawning habitat, substrate stabilization, and improved water quality

-     “Blue carbon” is removed from the air and water and stored in the sediment of vegetated coastal ecosystems, including seagrasses, salt marshes, and mangroves, through their trapping of sediments and seagrass tissue falling to the sea bed.

-    Seagrasses have been shown to store a large amount of carbon per unit area, but the amounts stored in seagrasses of Pacific Rim National Park Reserve are substantially lower than other estimates from around the globe.