Seaweed Farming for Carbon Storage: As Viable as Other Blue Carbon Habitat Reconstruction Methods According to New Research

     Blue carbon habitat reconstruction by planting seagrasses and mangrove trees is an established way to increase marine uptake of CO2 and has been incorporated into lots of projects that generate carbon credits. A new study in Nature Climate Change concludes that seaweed farming is another method that is competitive with the other blue carbon methods. Seaweed farming has long been a viable carbon sequestration method. I first read about it in Tim Flannery’s 2015 book Atmosphere of Hope.

     Most seaweed farming, or kelp farming, occurs in the waters of Southeast Asia. Consumption of different kinds of seaweed is most common there. According to Wikipedia:

“The largest seaweed-producing countries as of 2022 are China (58.62%) and Indonesia (28.6%); followed by South Korea (5.09%) and the Philippines (4.19%). Other notable producers include North Korea (1.6%), Japan (1.15%), Malaysia (0.53%), Zanzibar (Tanzania, 0.5%), and Chile (0.3%). Seaweed farming has frequently been developed to improve economic conditions and to reduce fishing pressure.”

Global production was over 35 million tons in 2019, according to the Food and Agriculture Organization (FAO). The U.S. produces about 23,000 tons with most coming from Alaska and Maine waters. In the U.S. farmers grow various types of seaweed which include dulse, bull kelp, ribbon kelp, and sugar kelp. They are used in sushi, salsas, sauces, salads, seasonings, and other food products.

     Seaweed is also cultivated for extracting its polysaccharides, including alginate, agar, and carrageenan, gelatinous substances known as hydrocolloids or phycocolloids. Hydrocolloids are used as food additives as gelling agents, emulsifying, thickening, and water retention. Like seagrasses and mangroves, seaweed also provides habitat.

     Seaweed farming has both positive and negative impacts but many of the negative impacts can be easily mitigated. Mangroves may be cut down for stakes, many seaweed farms are placed atop seagrass meadows, and the removal of eelgrass to plant seaweed has negative effects on water quality. Seaweed farms may also introduce or aid in the establishment of invasive species. The positive benefits include feeding humans, feeding livestock, creating biofuels, slowing climate change, and providing crucial habitat for marine life. Seaweed farming has a much lower impact than other aquaculture and land agriculture. It can also increase biodiversity and decrease ocean acidity. According to the NOAA, seaweeds pull more greenhouse gas from the water than salt marshes, eelgrass, and mangroves combined based on biomass. Seaweeds also consume nitrogen and phosphorous. Thus, constructing seaweed farms near ocean dead zones can help use up the excess nutrients. The NOAA is working to restore lost bull kelp areas in Puget Sound.

     According to Wikipedia:

“One way for seaweed farming to scale at terrestrial farming levels is with the use of ROVs, which can install low-cost helical anchors that can extend seaweed farming into unprotected waters.”

ROVs, or remotely operated underwater vehicles, are submersibles typically used in the offshore oil & gas industry.

     A large team of international researchers from multiple disciplines worked on the Nature Climate Change paper.  According to Phys.org:

“The work involved analyzing data collected by operators of 20 seaweed farms around the world. The researchers note that the farms they studied ranged in age from 2 to 300 years old and that they ranged in size from 1 to 15,000 hectares.”

The researchers noted that there was more carbon sequestered below older seaweed farms as would be expected. They also found that the average amount of carbon buried below all the farms studied was about twice that of sediment beds located near the farms.

“The researchers suggest that seaweed farming, especially in places where sediments naturally build up, can sequester carbon at rates near to those of some coastal environments, such as mangrove forests.”

     The U.N. and others have noted that more research is needed on quantifying the effectiveness of seaweed farming and this is a great step in that direction. The abstract of the paper is below:

Abstract

“Seaweed farming has emerged as a potential Blue Carbon strategy, yet empirical estimates of carbon burial from such farms remain lacking in the literature. Here, we quantify carbon burial in 20 seaweed farms distributed globally, ranging from 2 to 300 years in operation and from 1 to 15,000 ha in size. The thickness of sediment layers and stocks of organic carbon accumulated below the farms increased with farm age, reaching 140 tC ha−1 for the oldest farm. Organic carbon burial rates averaged 1.87 ± 0.73 tCO2e ha−1 yr−1 in farm sediments, twice that in reference sediments. The excess CO2e burial attributable to the seaweed farms averaged 1.06 ± 0.74 CO2e ha−1 yr−1, confirming that seaweed farming in depositional environments buries carbon in the underlying sediments at rates towards the low range of that of Blue Carbon habitats, but increasing with farm age.”

 

References:

 

Seaweed farms show potential for carbon storage that gets better with age. Bob Yirka. Phys.org. January 24, 2025. Seaweed farms show potential for carbon storage that gets better with age

Carbon burial in sediments below seaweed farms matches that of Blue Carbon habitats. Carlos M. Duarte, Antonio Delgado-Huertas, Elisa Marti, Beat Gasser, Isidro San Martin, Alexandra Cousteau, Fritz Neumeyer, Megan Reilly-Cayten, Joshua Boyce, Tomohiro Kuwae, Masakazu Hori, Toshihiro Miyajima, Nichole N. Price, Suzanne Arnold, Aurora M. Ricart, Simon Davis, Noumie Surugau, Al-Jeria Abdul, Jiaping Wu, Xi Xiao, Ik Kyo Chung, Chang Geun Choi, Calvyn F. A. Sondak, Hatim Albasri, …Pere Masque. Nature Climate Change volume 15, pages180–187 (2025). Carbon burial in sediments below seaweed farms matches that of Blue Carbon habitats | Nature Climate Change

Seaweed farming. Wikipedia. Seaweed farming - Wikipedia

Seaweed Aquaculture. NOAA Fisheries. Seaweed Aquaculture | NOAA Fisheries