With its beaches, an imperial villa and a view of Mount Fuji across the bay, the town of Hayama, Kanagawa Prefecture, is a greener, calmer alternative to the hustle and bustle of nearby Tokyo. But for all its picturesque qualities on land, Hayama’s coastal seas — like many across Japan — are in trouble.
“I have witnessed the rapid decline of seaweed species like arame and kajime since around 2016,” recounts Hayama Eelgrass Council member Katsunori Yamaki. “Fishermen, too, said they could no longer catch the abalone, turban shells and fish that had lived in the seaweed beds.”
Working with local fishers and schools, the Hayama Eelgrass Council began planting eelgrass in the town’s coastal seas before adding seaweed and marine mollusc species to their activities over time.
Recently, their restoration work has gained added impetus as a “blue carbon ecosystem.”
Coined by the United Nations Environment Programme in 2009, “blue carbon” refers to the carbon dioxide sequestered and stored by coastal habitats such as mangroves and seagrass beds. These highly efficient ecosystems occupy just 0.5% of the seafloor but contribute over 50% of oceans’ carbon burial, sequestering even more carbon by area than rainforests.
Unfortunately, scientists estimate roughly 50% of Earth’s blue carbon ecosystems have been lost in a decline that has yet to be reversed. The trend can be seen in Japan, where experts believe 20% to 36% of seagrass and seaweed ecosystems were lost between 1978 and 1992 due to human activities. The ensuing years saw continued decline, according to government data.
While the deterioration of Japan’s coastal ecology has long concerned scientists, officials and fishers, the government’s 2020 declaration that Japan would reduce its greenhouse gas emissions to net zero by 2050 boosted interest in conserving and restoring these habitats, this time for their carbon benefits.
Earlier this year, Japan became the first country to include carbon sequestered by seaweed — an understudied type of blue carbon ecosystem — in its national emissions inventory submitted to the U.N.
Blue carbon ecosystems reportedly sequestered 0.03% of Japan’s annual emissions in the year through March 2023. Experts say blue carbon projects — especially seaweed aquaculture — will need to be seriously expanded for blue carbon to contribute to Japan’s net zero goal. It’s far from a silver bullet.
Verifying the amount of carbon sequestered and stored by seaweed also presents a challenge, although Japanese scientists remain undeterred. Accurate calculations are imperative, as overstating a project’s carbon benefits risks public backlash, a pitfall that has plagued corporate-sponsored forest conservation projects over the years.
Still, blue carbon proponents emphasize that the full value of these ecosystems goes beyond the storage of carbon dioxide.
Extra benefits
The government has been keen on blue carbon for over a decade. Its 2013 basic plan on ocean policy promoted research into it, and the updated 2018 plan called for the implementation of blue carbon initiatives, spearheaded by the Ministry of Land, Infrastructure, Transport and Tourism. In January 2023, a cross-ministry Blue Carbon Liaison Council was established to coordinate government efforts to utilize blue carbon.
One way to incentivize such projects is through carbon offsets: tradable certificates that show how much carbon dioxide is sequestered or emissions are avoided by a given initiative.
Although, internationally, offsets have both proponents and critics, the Japanese government emphasizes carbon credit trading in its decarbonization strategy. It awards carbon credits for activities on land that reduce emissions against a business-as-usual baseline, such as energy-saving measures, the use of renewable energy — controversially, including woody biomass — and managing forests as carbon sinks.
A diver floats above sargassum, a type of seaweed, at the site of a blue carbon project near Iki island, Nagasaki Prefecture, in 2023.
| Iki City Hall
Aiming to use carbon credits to financially support coastal restoration projects in Japan, Tomohiro Kuwae, a member of the land ministry’s Port and Airport Research Institute, founded the Japan Blue Economy Association (JBE) in July 2020 — mere months before then-Prime Minister Yoshihide Suga declared Japan would achieve net zero emissions by 2050.
“I thought I could take three or so years to gradually develop a carbon credit system … but suddenly the government requested that I test it out as soon as possible,” Kuwae says.
Although JBE’s budget doesn’t come from the government, they work closely together, and it currently certifies blue carbon credits for 29 projects across Japan. Kuwae said he receives roughly 400 inquiries from companies and 100 from municipalities regarding credits per year.
To measure the amount of sequestered carbon, applicants hoping to receive credits — which are certified on an annual basis — multiply the area restored through the project by how much carbon dioxide the ecosystem can absorb per unit of area. An independent panel of experts evaluates each application, also considering whether the project is sustainable long-term.
The Hayama Eelgrass Council is one example of an existing restoration initiative that has, since 2022, received credits from JBE. The application process was fairly straightforward thanks to years of data on seagrass and seaweed beds the organization had compiled, Yamaki says.
“We are now using (the credits) to sustain our local conservation activities,” he explains.
The council invites local children and companies that purchase the credits on “blue carbon tours” to better understand the state of the ecosystem.
“I believe that if the sea improves, it will also create economic benefits — a blue economy — for the area,” Yamaki adds.
A volunteer prepares to plant eelgrass seedlings during a project to restore the natural ecosystem in Yokohama on April 13.
| REUTERS
So far, JBE’s carbon credits have found eager buyers.
“The projects themselves are not so large, and the amount of carbon credits is small too, but they still sell for a high price because many people want to support this kind of local project,” Kuwae says, noting that local companies are often the ones buying the credits. “They feel there’s a value (in the projects) beyond just the value of the carbon.”
Blue carbon ecosystems also produce various “co-benefits” such as supporting fisheries, protecting coastlines and providing cultural value, says Daniel Friess, a professor at Tulane University in New Orleans who studies blue carbon.
“Carbon can be seen as an umbrella to help conserve all of these other benefits to coastal communities,” he adds.
Avoiding greenwashing
While there is serious interest in blue carbon in Japan and around the world, projects face various challenges.
For one, gathering data on the specific movement and volume of sequestered carbon isn’t always straightforward, especially for seaweed ecosystems, which account for many of the JBE-certified projects.
Unlike mangroves and seagrass, which grow in sand or sediment where their sequestered carbon is stored, seaweed — including species like konbu and wakame commonly eaten in Japan — attach themselves to hard, rocky surfaces. Carbon sequestered through their photosynthesis is stored off-site, mostly in the deep sea, as old fronds are shed and drift away.
“Proving that link is much harder,” Friess says. As a result, the international scientific community has often excluded seaweed from the various types of blue carbon ecosystems.
Kuwae, however, sees opportunity. “As scientists, studying these unknown areas is the most exciting part,” he says.
Based on data he and other researchers have collected, JBE provides applicants with coefficients to calculate carbon sequestered by various kinds of seaweed and accumulated in the seabed, so that applicants don’t need to prove the link themselves. Similarly, the government used a “model on estimating long-term carbon sequestration (over 100 years) through … macroalgal (seaweed) beds” in its 2024 greenhouse gas inventory.
“Someone had to take a risk” and be the first to bring seaweed into the blue carbon fold, Kuwae says.
Wakame and other types of seaweed grow on an artificial reef in Shiraoi, Hokkaido, in 2023. The project receives carbon credits through the Japan Blue Economy Association.
| Hokkaido Aquaculture Promotion Corp.
However, the challenges to blue carbon don’t end there. According to Friess, high implementation and monitoring costs are a major factor limiting the number of blue carbon projects. And, although coastal ecosystems can be quite resilient, they are still often “on the front lines” of climate change impacts such as sea level rise, exacerbated storms and marine heat waves, he says. Warming seas are thought to be one cause of marine desertification — “isoyake” in Japanese — a common problem along Japan’s coasts.
Another challenge is avoiding accusations of greenwashing: misleading statements intended to make a product or practice seem more environmentally friendly than it really is.
In a 2022 paper, Friess and colleagues noted that “selling credits to organisations without credible plans for emissions reductions … (is) a political risk that could undermine public support for blue carbon more generally.”
Forest carbon credits offer a cautionary tale. Although forest credits have enjoyed widespread popularity among corporate buyers looking to offset their carbon dioxide emissions, critics argue that the benefits of such credits are often exaggerated. Scientists warn that offsets should never be used as a substitute for cutting emissions.
Although Japan’s blue carbon projects aren’t generating significant offsets, corporations with heavy carbon footprints do participate in JBE’s credit program, either as project co-implementers or credit buyers. The national government too, although positioning itself as a global leader on blue carbon, has been criticized by both domestic and international climate advocates for a decarbonization strategy they say is unfeasible.
In Friess’ view, given blue carbon projects’ currently limited scale, “we can be cautiously optimistic” that such initiatives won’t simply be used to obscure emissions on paper.
“Blue carbon is seen as a boutique carbon: You have relatively low supply, but relatively high quality and lots of co-benefits,” he says. “People who are willing to spend the money to invest in blue carbon … often have other conservation motives” than simply offsetting their own emissions.
Kuwae too is well aware of greenwashing concerns. “We can’t certify projects that aren’t successful,” he emphasizes. “If (the ecosystem) isn’t improving, it’s pointless. We certainly won’t award credits to projects based on future projections.”