Edible seaweed

Edible seaweeds are broadly classified by color: red (Rhodophyta), brown (Phaeophyceae), and green (Chlorophyta). The most widely consumed species include Porphyra spp. (nori), Laminaria and Saccharina (kombu), Undaria pinnatifida (wakame), and Gracilaria and Eucheuma (used for agar and carrageenan). In Japan, nori is essential for sushi and onigiri; in Korea, gim is roasted and seasoned; in China, kelp is used in soups and salads. Beyond Asia, seaweeds appear in Irish moss pudding, Welsh laverbread, and Hawaiian limu.¹

Seaweeds are low in calories but dense in nutrients: they provide dietary fiber, iodine, iron, calcium, magnesium, and vitamins A, C, E, and K. They contain unique polysaccharides such as fucoidan and alginate, which have shown antioxidant, anti-inflammatory, and prebiotic effects in studies.² However, iodine content varies widely among species, and excessive consumption can lead to thyroid dysfunction. Some compounds may also bind heavy metals, so sourcing from clean waters is important.³

Commercial seaweed farming began in Japan in the 17th century and has expanded globally, with China, Indonesia, and South Korea leading production. Seaweed aquaculture requires no freshwater, fertilizer, or land, and it can absorb carbon and nitrogen, mitigating eutrophication. Integrated multi-trophic aquaculture (IMTA) pairs seaweed with fish or shellfish farms to create balanced ecosystems.⁴ Wild harvesting remains important in some regions, but overharvesting has led to management regulations.⁵

Beyond food, edible seaweeds have niche uses: Palmaria palmata (dulse) is eaten raw or fried in Atlantic Canada; Caulerpa lentillifera (sea grapes) is a delicacy in Southeast Asia with a popping texture. Seaweed extracts are used in cosmetics, pharmaceuticals, and bioplastics. Historically, Welsh miners ate laverbread for its mineral content, and Pacific Islanders used Gracilaria in traditional dishes. Some species, like Asparagopsis taxiformis, are being studied to reduce methane emissions from livestock when added to feed.⁶

Nori

Dried sheets of Porphyra seaweed, used in sushi.

Kombu

Kelp species used to make dashi broth.

Wakame

Brown seaweed with a sweet flavor, used in miso soup.

Agar

Gelatinous substance derived from red algae, used as a thickener.

Carrageenan

Polysaccharide extracted from red seaweeds, used as a stabilizer.