In recent years, seaweed farming has become a global agricultural practice, providing food, source material for various chemical uses (such as carrageenan), cattle feeds and fertilizers.

Due to their importance in marine ecologies and for absorbing carbon dioxide, recent attention has been on cultivating seaweeds as a potential climate change mitigation strategy for biosequestration of carbon dioxide, alongside other benefits like nutrient pollution reduction, increased habitat for coastal aquatic species, and reducing local ocean acidification.

[5] The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.

[14][15] Alternatively, pneumatocysts (gas filled "bubbles") can keep the macroalgae thallus afloat; fronds are transported by wind and currents from the coast into the deep ocean.

[15] As macroalgae takes up carbon dioxide and releases oxygen in the photosynthesis, macroalgae fronds can also contribute to carbon sequestration in the ocean, when the macroalgal fronds drift offshore into the deep ocean basins and sink to the sea floor without being remineralized by organisms.

[16][17][18] Nowadays a number of vectors—e.g., transport on ship hulls, exchanges among shellfish farmers, global warming, opening of trans-oceanic canals—all combine to enhance the transfer of exotic seaweeds to new environments.

Since the piercing of the Suez Canal, the situation is particularly acute in the Mediterranean Sea, a 'marine biodiversity hotspot' that now registers over 120 newly introduced seaweed species -the largest number in the world.

The seven most cultivated taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme.

Eucheuma and K. alvarezii are attractive for carrageenan (a gelling agent); Gracilaria is farmed for agar; the rest are eaten after limited processing.

[23][24] Seaweed farming has frequently been developed to improve economic conditions and to reduce fishing pressure.

[32] Seaweed is consumed across the world, particularly in East Asia, e.g., Japan, China, Korea, Taiwan and Southeast Asia, e.g. Brunei, Singapore, Thailand, Burma, Cambodia, Vietnam, Indonesia, the Philippines, and Malaysia,[33] as well as in South Africa, Belize, Peru, Chile, the Canadian Maritimes, Scandinavia, South West England,[34] Ireland, Wales, Hawaii and California, and Scotland.

Gim (김, Korea), nori (海苔, Japan) and zicai (紫菜, China) are sheets of dried Porphyra used in soups, sushi or onigiri (rice balls).

In northern Belize, seaweed is mixed with milk, nutmeg, cinnamon and vanilla to make "dulce" ("sweet").

Carrageenan is used in salad dressings and sauces, dietetic foods, and as a preservative in meat and fish, dairy items and baked goods.

In some emerging countries, seaweed is harvested daily to support communities.Seaweed is sometimes used to build roofs on houses on Læsø in Denmark.

[61] The so-called "stinging seaweed" Microcoleus lyngbyaceus is a filamentous cyanobacteria which contains toxins including lyngbyatoxin-a and debromoaplysiatoxin.

Direct skin contact can cause seaweed dermatitis characterized by painful, burning lesions that last for days.

[1][62] Bacterial disease ice-ice infects Kappaphycus (red seaweed), turning its branches white.

When stressed by hunger, their jaws and teeth enlarge, and they form "fronts" and hunt for food collectively.