This isn't the first time we've heard about this, but it is the first global analysis of how much carbon is stored by seagrasses: According to new research, publish in Nature Geosciences, seagrasses can store up to twice as much carbon per square kilometer as above ground forests.
In terms of numbers, coastal seagrasses can store 83,000 metric tons of carbon per square kilometer, versus 30,000 tons for a typical forest. Furthermore, though seagrasses occur in just 0.2% of the world's oceans, they are responsible for storing over 10% of all the carbon buried annually in the ocean. 90% of the carbon storied by seagrasses is sequestered in the soil anchoring the grass, where it can form carbon stores several meters deep. In some cases these seagrass meadows have been accumulating carbon for thousands of years.
If you guessed there was a "seagrasses are threatened" angle in this, you're right.
The paper finds that 29% of all historic seagrass meadows have been destroyed, primarily due to dredging and water pollution, with 1.5% of seagrass meadows destroyed each year. Should this continue, the destruction of these meadows will result in carbon emissions one-quarter as great as deforestation.