Most of the seaweed you eat comes from farms in East and Southeast Asia. About 97% of the world’s seaweed supply is cultivated through aquaculture rather than harvested from the wild, and that ratio has held steady for over 50 years. China alone produces more than half of all seaweed globally, followed by Indonesia, South Korea, the Philippines, and North Korea.
Where Seaweed Is Farmed
China dominates global seaweed production, accounting for roughly 57% of the world total with over 20 million tonnes in 2019. Indonesia is the second largest producer at nearly 10 million tonnes (about 28%), followed by South Korea at 5%, the Philippines at 4%, and North Korea at just under 2%. Together, these five countries produce more than 95% of the world’s seaweed.
The remaining 3% that isn’t farmed comes from wild harvesting along coastlines in places like Norway, France, Ireland, Canada, and parts of the United States. Wild-harvested seaweed tends to supply smaller specialty markets and local food traditions rather than the mass-produced sheets and snacks you find in grocery stores.
The Main Types You’ll Find
Out of more than 200 commercially used seaweed species, only about 10 are farmed at large scale. They fall into three color groups, each with varieties you’ve likely seen on a menu or store shelf.
- Nori is a red seaweed (Porphyra or Pyropia species) best known as the dark, papery wrapper around sushi rolls. It’s remarkably protein-rich, containing up to 33% protein by dry weight, which is comparable to many high-protein plants.
- Wakame is a brown seaweed (Undaria pinnatifida) commonly found in miso soup and seaweed salads. It contains about 17% protein by dry weight and has a mild, slightly sweet flavor.
- Kombu is another brown seaweed (Saccharina japonica) used heavily in Japanese cooking as the base for dashi broth. It’s prized for its intense umami flavor.
Green seaweeds like sea lettuce also appear in commercial products, though they’re less common in Western grocery stores. In parts of Southeast Asia, species like Caulerpa (sometimes called sea grapes) are eaten fresh as a salad ingredient.
How Seaweed Farming Works
Seaweed farming doesn’t require soil, freshwater, or fertilizer. The plants absorb nutrients directly from ocean water and convert dissolved CO2 into biomass through photosynthesis, making it one of the lowest-input forms of food production.
Nori farming offers a good example of how the process works. Centuries ago, Japanese fishermen noticed that seaweed naturally colonized the bamboo stakes holding their fishing nets. They started driving stakes into shallow seabeds deliberately to encourage growth, eventually developing horizontal net systems along the water’s surface. Modern nori farms still use nets, but the process now begins indoors. Scientists control water temperature in tanks to guide nori spores through their early life stages. Once the spores reach the right developmental phase, they’re seeded onto nets and transferred to the ocean, where they grow into the leafy sheets that get harvested.
Other species use different setups. Kombu and wakame are typically grown on long ropes suspended in the water column, while tropical species like those farmed in Indonesia and the Philippines often grow on lines staked to the shallow seafloor. Growing cycles vary from a few weeks for fast-growing tropical species to several months for cold-water kelps.
From Ocean to Package
Raw seaweed is highly perishable. Once harvested, it needs to be processed quickly to prevent spoilage. Drying is the most common preservation method, and the industry uses several approaches depending on the end product. Some seaweed is sun-dried on racks (still common in smaller operations), while large-scale producers use industrial hot-air dryers or freeze-drying equipment.
Nori goes through additional steps. After harvesting, the sheets are washed in fresh water, shredded, and spread into thin layers on frames, similar to traditional papermaking. These layers are then dried and often roasted or toasted, which gives the final product its characteristic dark color, crisp texture, and toasty flavor. The finished sheets are graded by color, thickness, and sheen before packaging.
Seaweed powder is another growing product format, used both as a seasoning for its salty, umami-rich flavor and as an ingredient in smoothies, supplements, and processed foods. Dried seaweed snacks, seasoned with salt and sesame oil, have become one of the fastest-growing segments of the market. The global edible seaweed market was valued at about $14 billion in 2025 and is projected to reach $26 billion by 2034.
Environmental Benefits of Seaweed Farms
Seaweed farming is often described as one of the most sustainable forms of food production. The plants pull carbon dioxide from seawater and convert it into biomass efficiently, and farms can absorb excess nitrogen and other nutrients that would otherwise fuel harmful algal blooms. Seaweed operations also create underwater habitat for fish and invertebrates, buffer shorelines against wave damage, and can create local refuges from ocean acidification.
The climate benefits are real but modest. Modeling of large-scale seaweed farming in British Columbia found that, depending on growth rates and how the harvested seaweed is used, farms could offset between 0.3% and 13% of the province’s annual greenhouse gas emissions. The biggest climate gains come not from sinking seaweed to the ocean floor (where most of the carbon gets released back into the water) but from using harvested seaweed to replace higher-emission products like animal feed or synthetic fertilizers.
Safety Considerations
Seaweed is nutritious, but two things are worth knowing about: iodine and heavy metals. Seaweed concentrates iodine from seawater, and some species, particularly kombu, contain very high levels. The tolerable upper intake for iodine in adults is 600 micrograms per day, and a single serving of kombu can exceed that. If you eat seaweed regularly, varying the types you consume helps keep iodine intake in a reasonable range. Nori tends to be much lower in iodine than kombu or wakame.
Heavy metals like arsenic, cadmium, lead, and mercury can also accumulate in seaweed tissue, though levels vary widely by species, growing location, and water quality. Notably, most countries haven’t established formal maximum limits for heavy metals in edible seaweed products, with the exception of cadmium in seaweed-based supplements. France recommends a maximum iodine concentration of 2,000 mg per kilogram of dry seaweed, while Germany recommends capping daily iodine intake from seaweed at 500 micrograms. Buying from established brands that test their products and sourcing seaweed grown in clean waters are the most practical ways to minimize risk.