If you're like me, you probably never think about seagrass until an ocean wave wraps a slippery ribbon of the plant around an unsuspecting limb. But beds of the marine grasses are one of the most efficient carbon sinks on the planet, putting away organic carbon 35 times faster than tropical forests, and holding onto the molecules for many times longer. But seagrass ecosystems, like nearly all ecosystems on Earth, are threatened by human activities, and little work has been done to determine just how much carbon the disturbed seagrass beds will release.
In a new study, a team of Australian researchers sought to help fill in that gap by looking at Jervis Bay, a site off the eastern coast of the island nation where seismic testing in the 1960s left massive, gaping holes of bare sand in the seagrass meadows. The researchers took soil samples from the exposed holes, as well as the outer edges where the plant has begun to grow back, and undisturbed seagrass fields. They found the seismic testing had blasted away carbon that had taken up to 6,000 years to amass; the disturbed grass beds lost 72 percent of their carbon stocks compared to the undisturbed meadows. Promisingly, roughly half of the carbon lost had already been recovered in the recuperating areas of seabed, where the grasses have begun to grow again over the last decade.
Seismic testing is a relatively rare form of disturbance, so more work needs to be done to determine if these results hold up for other human-induced disturbances such as coastal development, dredging, eutrophication, or oil spills. But the study does show that worldwide seagrass declines deserve attention; the grass beds store enough carbon that their demise would be a significant contributor to global warming.