Deep Seagrass Bed Could Stall Climate Change, If Climate Change Doesn't Kill It First

Dec 17, 2018
Originally published on December 19, 2018 4:00 pm

Amid a sea of dire climate change news, researchers say they've found a rare bright spot.

A meadow of seagrass among Australia's Great Barrier Reef — estimated to be twice the size of New Jersey — is soaking up and storing carbon that would otherwise contribute to global warming.

Scientists call this carbon-removal powerhouse a "blue carbon sink." The term refers to an ocean or coastal ecosystem — including seagrasses, salt marshes and mangrove forests — that captures carbon compounds from the atmosphere, effectively removing carbon dioxide, a known greenhouse gas that contributes to climate change.

"These coastal Blue Carbon ecosystems can sequester or remove carbon from the atmosphere about four times the rate of terrestrial forests on land, and they store about 10 times more carbon in the system itself compared to forest on land," says Jennifer Howard, director of marine climate change at Conservation International, in an interview with NPR's Michel Martin.

A new study published in Biology Letters suggests that these deep-water seagrass meadows play a more central role in the carbon cycle than previously thought. Authors Peter Macreadie of Deakin University in Australia, and Paul York and Michael Rasheed, both from James Cook University, compared carbon stocks from deep-water, mid-water and shallow-water seagrass living at Lizard Island in the Great Barrier Reef. The researchers found that the seagrass in deeper regions contained similar carbon levels as seagrass in shallower waters.

Previously, data has been very sparse on deep-water seagrass as Blue Carbon sinks. They're hard to get to, buried deep beneath water and invisible even from satellite.

"You usually have to throw somebody in the water with a scuba mask to go actually find them," Howard says. "And because of that we just don't know how many of these large patches of sea grasses there actually are out there."

Howard says her organization has mapped nearly 109,000 square miles, "but that's probably less than half of what's actually out there."

What's more, that number only reflects the more detectable, shallower seagrasses. As for the deeper-water seagrasses analyzed in the study, the Australian researchers figured that if the deep-water seagrass stores a comparable amount of carbon as other deep-water meadows in the region, the area around the Great Barrier Reef may be sequestering tens of millions of tons of carbon.

Worldwide, Howard says, "We think that there's probably about several billion tons of carbon locked away in these seagrass meadows" — ecosystems, she says, that exist on every continent except Antarctica.

These new findings are valuable to policymakers working to curb climate change, according to Howard. But the value of these ecosystems, she says, disappears if they're not protected.

"When you destroy those ecosystems, all that carbon can be re-released back into the atmosphere. So, through poor land use management or through degradation, the significant carbon sink can actually become a global carbon source."

Seagrasses are vanishing globally at a rate of 1.5 percent per year, Reuters reports, a decline that's comparable to coral reefs and tropical rainforests. Scientists point to coastal development as the culprit behind water pollution that perpetuates erosion. And, while seagrasses can mitigate climate change, climate change can also destroy the grasses.

"When you have pollutants and too much sediment running down the river, it blocks out the light, it buries the seagrass and they start to die," Howard says.

She says the solution to alleviating seagrass loss has to be "land-based."

"You're going to have to address the pollution component first. Remove the threat, and then planting [seagrass] could be a very viable option to increase carbon stock."


NPR's Chad Campbell and Martha Wexler produced and edited this story for broadcast.

Copyright 2018 NPR. To see more, visit https://www.npr.org.

MICHEL MARTIN, HOST:

Staying on the subject of climate change for a few more minutes, there was another bright spot this past week amid all the dire warnings we have been hearing about the effects of climate change. And it is a very big bright spot - a meadow of seagrass some 50 feet below the surface off the coast of Australia. It is said to be twice the size of New Jersey, and it's soaking up and storing a lot of carbon that otherwise would contribute to global warming.

Jennifer Howard is director of marine climate change at Conservation International. She has spent years studying so-called carbon sinks, and she's come in to explain the latest discovery. Jennifer Howard, thanks so much for joining us.

JENNIFER HOWARD: Thank you so much.

MARTIN: So, first, I'm going to ask you to walk me through what is a blue carbon sink. And why is it called that?

HOWARD: Sure. So blue carbon sinks really refer to three main ecosystems - seagrass being one of them, of course, then, also, salt marshes and mangrove forests. These ecosystems are powerhouses when it comes to removing carbon out of the atmosphere but, even more importantly, storing it in the soil beneath them. So these coastal blue carbon ecosystems can sequester or remove carbon from the atmosphere about four times the rate of terrestrial forests on land. And they store about 10 times more carbon in the system itself.

MARTIN: How does it work? How does it do what it does?

HOWARD: So seagrasses are just flowering grasses that live underwater. So, like all plants, they remove carbon dioxide from the atmosphere and convert that into the actual plant matter itself so the leaves, the flowers, the roots. And so, then, when those seagrasses die, all of that gets buried underneath. And because of their root system, which is very intricate, it kind of locks it down and holds it in there.

But the unique thing about a blue carbon ecosystem is that saltwater really inhibits bacterial breakdown of that material. So, basically, once the plants die, they're preserved within the soil. And, again, in this study, particularly, these are seagrasses next to the Great Barrier Reef. And having the seagrasses that absorb that CO2 are actually protecting the reefs against ocean acidification degradation.

MARTIN: So is the news, here, that this exists, or is the news here of what these carbon sinks actually can accomplish, can do for us?

HOWARD: Well, you know, the science behind what these systems are and what they can do for us is pretty well-established. The interesting thing about this study, in particular, is that seagrass beds are very hard to find. Because they're underwater, satellite imagery is - it's very difficult to pick them up and find where they are. So you usually have to throw somebody in the water with a scuba mask to go actually find them. So...

MARTIN: Couldn't you invite them, nicely, to go in with a scuba mask?

HOWARD: (Laughter).

MARTIN: You have to throw them in?

HOWARD: We could - I think most people don't mind scuba-diving in...

MARTIN: (Laughter).

HOWARD: ...Tropical locations...

MARTIN: Yeah.

HOWARD: ...For sure, near the Great Barrier Reef.

MARTIN: But this is something that requires some effort to find.

HOWARD: Yeah, absolutely. And, because of that, we just don't know how many of these large patches of seagrasses there actually are out there.

MARTIN: So tell me more about what's amazing. Is it that - is the - how much work is this particular patch? Or can you sort of quantify how much carbon this area is soaking up? Or what do we think it's contributing?

HOWARD: Probably on average. And I haven't done the calculations for this particular patch and its size. But, you know, we think that there's probably about several billion tons of carbon locked away in the seagrass meadows all over the world. And the unique thing about these ecosystems, as well, that I really want to mention is not only are they fantastic for removing carbon from the atmosphere, which makes them important for all climate change mitigation policy, but when you destroy those ecosystems, all that carbon can be rereleased back into the atmosphere.

MARTIN: That was going to be - my question is that - are these deep seagrasses endangered? Is this something that we should be concerned about?

HOWARD: So, again, we don't know that much about deep seagrasses. But, in general, looking globally, seagrasses are being lost at about 2 percent per year, which is very significant. But most of that loss is really coming from poor water quality. What happens when you have pollutants and too much sediment running down the river, it blocks out the light. It buries the seagrass, and they start to die. The solution to that is really going to be land-based. You're going to have to address the pollution component first.

MARTIN: And, finally, do scientists suggest that we should be cultivating seagrass? Is that even a thing? Can that be done?

HOWARD: It can be done. I think, though, that one thing to keep in mind is that seagrasses are very prolific. And so, if they're not currently being seen there, there's a reason why. So if you just go and plant in these areas, it's probably not going to do very well.

MARTIN: That's Jennifer Howard, the marine climate change director at Conservation International. She was commenting on the findings of Peter Macreadie at Deakin University in Australia. Jennifer, thanks so much for talking to us.

HOWARD: Thank you. This was great. Transcript provided by NPR, Copyright NPR.