Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form, it consists of the management of naturally found batches. In its most advanced form, it consists of fully controlling the life cycle of the algae.
The top seven most cultivated seaweed taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme. Eucheuma and K. alvarezii are farmed for carrageenan (a gelling agent); Gracilaria is farmed for agar; while the rest are farmed for food. The largest seaweed-producing countries are China, Indonesia, and the Philippines. Other notable producers include South Korea, North Korea, Japan, Malaysia, and Zanzibar (Tanzania). Seaweed farming has frequently been developed as an alternative to improve economic conditions and to reduce fishing pressure and overexploited fisheries.
Global production of farmed aquatic plants, overwhelmingly dominated by seaweeds, grew in output volume from 13.5 million tonnes in 1995 to just over 30 million tonnes in 2016. As of 2014, seaweed was 27% of all marine aquaculture. Seaweed farming is a carbon negative crop, with a high potential for climate change mitigation . The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.
Seaweed farming began in Japan as early as 1670 in Tokyo Bay. In autumn of each year, farmers would throw bamboo branches into shallow, muddy water, where the spores of the seaweed would collect. A few weeks later these branches would be moved to a river estuary. The nutrients from the river would help the seaweed to grow.
In the 1940s, the Japanese improved this method by placing nets of synthetic material tied to bamboo poles. This effectively doubled the production. A cheaper variant of this method is called the hibi method — simple ropes stretched between bamboo poles. In the early 1970s, there was a recognized demand for seaweed and seaweed products, outstripping supply, and cultivation was viewed as the best means to increase productions.
In the tropics, commercial cultivation of Caulerpa lentillifera (sea grapes) was pioneered in the 1950s in Cebu, Philippines, after accidental introduction of C. lentillifera to fish ponds in the island of Mactan. This was further developed by local research, particularly through the efforts of Gavino Trono, since recognized as a National Scientist of the Philippines. Local research and experimental cultures led to the development of the first commercial farming methods for other warm-water algae (since cold-water red and brown edible algae favored in East Asia do not grow in the tropics), including the first successful commercial cultivation of carrageenan-producing algae. These include Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., and Halymenia durvillei. In 1997, it was estimated that 40,000 people in the Philippines made their living through seaweed farming. The Philippines was the world's largest producer of carrageenan for several decades, until it was overtaken by Indonesia in 2008.
The practice of seaweed farming has long since spread beyond Japan and the Philippines. Cultivation is also common in all of southeast Asia, Canada, Great Britain, Spain, and the United States.
In the 2000s, Seaweed farming has been getting increasing attention due to its potential for mitigating both climate change and other environmental issues, such as agricultural runoff. Seaweed farming can be mixed with other aquaculture, such as shellfish, to improve water bodies, such as in the practices developed by American non-profit GreenWave. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.
The earliest seaweed farming guides in the Philippines recommended the cultivation of Laminaria seaweed and reef flats at approximately one meter's depth at low tide. They also recommended cutting off seagrasses and removing sea urchins before farm construction. Seedlings are then tied to monofilament lines and strung between mangrove stakes pounded into the substrate. This off-bottom method is still one of the primary methods used today.
There are new long-line cultivation methods that can be used in deeper water approximately 7 meters in depth. They use floating cultivation lines anchored to the bottom and are the primary methods used in the villages of North Sulawesi, Indonesia. Species cultured by long-line include those of the genera Saccharina, Undaria, Eucheuma, Kappaphycus, and Gracilaria.
Cultivation of seaweed in Asia is a relatively low-technology business with a high labor requirement. There have been many attempts in various countries to introduce high technology to cultivate detached plants growth in tanks on land in order to reduce labor, but they have yet to attain commercial viability.
There has been considerable discussion as to how seaweeds can be cultivated in the open ocean as a means to regenerate decimated fish populations and contribute to carbon sequestration. Notably, Tim Flannery has highlighted how growing seaweeds in the open ocean, facilitated by artificial upwelling and substrate, can enable carbon sequestration if seaweeds are sunk below a depth of one kilometer. Similarly, the NGO Climate Foundation and a number of permaculture experts have posited that the offshore mariculture of seaweed ecosystems can be conducted in ways that embody the core principles of permaculture, thereby constituting Marine Permaculture. The concept envisions using artificial upwelling and floating, submerged platforms as substrate to replicate natural seaweed ecosystems that provide habitat and the basis of a trophic pyramid for marine life. Following the principles of permaculture, seaweeds and fish can be sustainably harvested while sequestering atmospheric carbon. As of 2020, a number of successful trials have taken place in Hawaii, the Philippines, Puerto Rico and Tasmania. The idea has received substantial public attention, notably featuring as a key solution covered by Damon Gameau’s documentary 2040 and in the book Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming edited by Paul Hawken.
Several environmental problems can result from seaweed farming. Sometimes seaweed farmers cut down mangroves to use as stakes for their ropes. This, however, negatively affects farming since it reduces the water quality and mangrove biodiversity due to depletion. Farmers may also sometimes remove eelgrass from their farming areas. This, however, is also discouraged, as it adversely affects water quality.
Seaweed farming helps to preserve coral reefs by increasing diversity where the algae and seaweed have been introduced, and it also provides an added niche for local species of fish and invertebrates. Farming may be beneficial by increasing the production of herbivorous fishes and shellfish in the area. Pollnac & et al 1997b harvnb error: no target: CITEREFPollnacet_al1997b (help) reported an increase in Siginid population after the start of extensive farming of eucheuma seaweed in villages in North Sulawesi, Indonesia.
Seaweed culture can also be used to capture, absorb, and eventually incorporate excessive nutrients into living tissue. "Nutrient bioextraction" is the preferred term for bioremediation involving cultured plants and animals. Nutrient bioextraction (also called bioharvesting) is the practice of farming and harvesting shellfish and seaweed to remove nitrogen and other nutrients from natural water bodies. (See main article Nutrient pollution.)
There has been considerable attention to how large-scale seaweed cultivation in the open ocean can act as a form of carbon sequestration to mitigate climate change. A number of academic studies have demonstrated that nearshore seaweed forests constitute a source of blue carbon, as seaweed detritus is carried by wave currents into the middle and deep ocean thereby sequestering carbon. Moreover, nothing on earth sequesters carbon faster than macrocystis pyrifera (also known as giant kelp) which can grow up to 60m in length and as rapidly as 50 cm a day in ideal conditions. It has therefore been suggested that growing seaweeds at scale can have a significant impact on climate change. According to one study, covering 9% of the world’s oceans with kelp forests “could produce sufficient biomethane to replace all of today’s needs in fossil fuel energy, while removing 53 billion tons of CO2 per year from the atmosphere, restoring pre-industrial levels”. As well as climate change mitigation, seaweed farming may be an initial step towards adapting to inevitable environmental constraints that may arise as a result of climate change in the near future. These include essential shoreline protection through the dissipation of wave energy, especially important to mangrove coasts. Carbon dioxyde intake would lower pH locally which will be highly beneficial to calcifiers like crustaceans or in preventing the irreversibility of coral bleaching. Finally, seaweed farming would provide a strong oxygen input to coastal waters, thus countering the effects of ocean deoxygenation through the rising ocean temperature . 
In Japan alone, the annual production value of nori amounts to US$2 billion and is one of the world's most valuable crops produced by aquaculture. The high demand for seaweed production provides plentiful opportunities and work for the local community. A study conducted by the Philippines showed that plots of approximately one hectare could have a net income from eucheuma farming that was 5 to 6 times that of the minimum average wage of an agriculture worker. In the same study, they also saw an increase in seaweed exports from 675 metric tons (MT) in 1967 to 13,191 MT in 1980, which doubled to 28,000 MT by 1988.
Seaweed farming has had widespread socio-economic impacts in Tanzania, and has become a very important source of resources for women, and is the third biggest contributor of foreign currency to the country. 90% of the farmers are women, and much of it is used by the skincare and cosmetics industry.
Zanzibar's seaweed growers face a changing climate. Here, a farmer tends to her farm in Paje, on the southeast coast of the island.
Mwanaisha Makame and Mashavu Rum, who have been farming seaweed on beautiful Zanzibar island for 20 years, wade through the low tide to their farm.
The seaweed grows underwater for 45 days. When it reaches one kilogram, the women pick it and dry it, then pack it in bags to be exported to countries like China, Korea and Vietnam. There, it's used in medicines and shampoos.
The farmers have a lot of problems due to climate change. Two decades ago, 450 seaweed farmers roamed Paje. Now, only about 150 farmers remain.
Mwanaisha holds up a healthy clump of seaweed. Then she holds up seaweed the farmers won't be able to use. A hard white substance grows on it - ice-ice disease, caused by higher ocean temperatures and intense sunlight.
The seaweed farmers learned how to make soap from their seaweed at the Zanzibar Seaweed Center, a business that started as an NGO in 2009. At their homes, they mix water, ground seaweed powder, coconut oil, caustic soda and essential oils in a large plastic tub.
Later in the week, the seaweed farmers will sell their finished soaps in Zanzibar town or to regular local customers. As seaweed levels decline, they have found a way to increase the value of their work.
The finished product - a bar of seaweed soap.
Farmed seaweed is used in a number of different industrially produced products, directly as food, and as source materials for things like biofuels.
Many seaweeds are used to produced derivative chemicals that can be used for various industrial, pharmaceutical or food products. Two major derivitative products are Carrageenan and Agar. However, there are a wide range of bioactive ingredients that can be used for a variety of industries, such as the pharmaceutical industry, industrial food, and the cosmetic industry.
Carrageenans or carrageenins (// karr-ə-gee-nənz, from Irish carraigín, "little rock") are a family of natural linear sulfated polysaccharides that are extracted from red edible seaweeds. The most well-known and still most important red seaweed used for manufacturing the hydrophilic colloids to produce carrageenan is Chondrus crispus (Irish moss) which is a dark red parsley-like plant that grows attached to the rocks. Carrageenans are widely used in the food industry, for their gelling, thickening, and stabilizing properties. Their main application is in dairy and meat products, due to their strong binding to food proteins. In recent years, carrageenans have emerged as a promising candidate in tissue engineering and regenerative medicine applications as they resemble native glycosaminoglycans (GAGs). They have been mainly used for tissue engineering, wound coverage and, drug delivery.
Carrageenans contain 15-40% ester-sulfate content, which makes anionic polysaccharide. They can be mainly categorized into three different classes based on their sulfate content. Kappa-carrageenan has one sulfate group per disaccharide, iota-carrageenan has two, and lambda-carrageenan has three. 
Gelatinous extracts of the Chondrus crispus seaweed have been used as food additives since approximately the fifteenth century. Carrageenan is a vegetarian and vegan alternative to gelatin in some applications or may be used to replace gelatin in confectionery. There is no clinical evidence for carrageenan as an unsafe food ingredient, mainly because its fate after digestion is inadequately determined.The first commercial cultivation of Eucheuma and Kappaphycus spp. for carrageenan was developed in the Philippines. The global top producers of carrageenan are the Philippines and Indonesia. Carrageenan, along with agar, are used to produce traditional jelly deserts in the Philippines called gulaman.
Agar is a mixture of two components: the linear polysaccharide agarose, and a heterogeneous mixture of smaller molecules called agaropectin. It forms the supporting structure in the cell walls of certain species of algae, and is released on boiling. These algae are known as agarophytes, and belong to the Rhodophyta (red algae) phylum.
Agar has been used as an ingredient in desserts throughout Asia, and also as a solid substrate to contain culture media for microbiological work. Agar can be used as a laxative, an appetite suppressant, a vegetarian substitute for gelatin, a thickener for soups, in fruit preserves, ice cream, and other desserts, as a clarifying agent in brewing, and for sizing paper and fabrics.The gelling agent in agar is an unbranched polysaccharide obtained from the cell walls of some species of red algae, primarily from tengusa (Gelidiaceae) and ogonori (Gracilaria). For commercial purposes, it is derived primarily from ogonori.
Edible seaweed, or sea vegetables, are seaweeds that can be eaten and used for culinary purposes. They typically contain high amounts of fiber. They may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae.
Seaweeds are also harvested or cultivated for the extraction of polysaccharides such as alginate, agar and carrageenan, gelatinous substances collectively known as hydrocolloids or phycocolloids. Hydrocolloids have attained commercial significance, especially in food production as food additives. The food industry exploits the gelling, water-retention, emulsifying and other physical properties of these hydrocolloids.
Most edible seaweeds are marine algae whereas most freshwater algae are toxic. Some marine algae contain acids that irritate the digestion canal, while some others can have a laxative and electrolyte-balancing effect. Most marine macroalgae are nontoxic in normal quantities, but members of the genus Lyngbya are potentially lethal. Typically poisoning is caused by eating fish which have fed on Lyngbya or on other fish which have done so. This is called ciguatera poisoning. Handling Lyngbya majuscula can also cause seaweed dermatitis. Some species of Desmarestia are highly acidic, with vacuoles of sulfuric acid that can cause severe gastrointestinal problems.The dish often served in western Chinese restaurants as 'Crispy Seaweed' is not seaweed but cabbage that has been dried and then fried.
Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made from seaweed (macroalgae) it can be known as seaweed fuel or seaweed oil.
Several companies and government agencies are funding efforts to reduce capital and operating costs and make algae fuel production commercially viable. Like fossil fuel, algae fuel releases CO
2 when burnt, but unlike fossil fuel, algae fuel and other biofuels only release CO
2 recently removed from the atmosphere via photosynthesis as the algae or plant grew. The energy crisis and the world food crisis have ignited interest in algaculture (farming algae) for making biodiesel and other biofuels using land unsuitable for agriculture. Among algal fuels' attractive characteristics are that they can be grown with minimal impact on fresh water resources, can be produced using saline and wastewater, have a high flash point, and are biodegradable and relatively harmless to the environment if spilled. Algae cost more per unit mass than other second-generation biofuel crops due to high capital and operating costs, but are claimed to yield between 10 and 100 times more fuel per unit area. The United States Department of Energy estimates that if algae fuel replaced all the petroleum fuel in the United States, it would require 15,000 square miles (39,000 km2), which is only 0.42% of the U.S. map, or about half of the land area of Maine. This is less than 1⁄7 the area of corn harvested in the United States in 2000.
"We're hoping to be at parity with fossil fuel-based petroleum in the year 2017 or 2018, with the idea that we will be at several billions of gallons," Rosenthal told SolveClimate News in a phone interview.
This article incorporates text from a free content work. Licensed under CC BY-SA 3.0 IGO License statement/permission on Wikimedia Commons. Text taken from In brief, The State of World Fisheries and Aquaculture, 2018, FAO, FAO.