Seaweed farming is the practice of cultivating and harvesting seaweed or algae. Some seaweed farmers manage naturally occurring crops, whilst others fully control the growing process, from seed to harvest.

Seaweed are classified as protist. Seaweed are plant-like protists that has been farmed and cultivated for centuries in Asia. In recent years, as its popularity has spread, seaweed farming has expanded rapidly around the globe.

World production of seaweed grew from 10.6 million tonnes in 2000 to 32.4 million tonnes in 2018 according to the Food and Agriculture Organization of the United Nations (FAO). In 2018, farmed seaweed represented 97.1 percent by volume of total production.

The value of the industry is estimated at USD 6 billion. In Japan, the annual production value of nori is worth around USD 2 billion, making it one of the world’s most valuable aquaculture species.

Diversity of species
The seaweed family is truly diverse, with more than 1,800 species of green algae, 2,000 species of brown algae, and well over 7,200 species of red algae growing around the world. In addition, there is estimated to be between 200,000 and 800,000 species of microalgae.

The most commonly cultivated seaweeds are Eucheuma spp. and Kappaphycus alvarexii, which are farmed for the natural gelling agent carrageenan;  Gracilaria spp. are important for agar; Saccharina spp. (kelp), Undaria pinnatifida (Wakame), Pyropia spp. (Nori) and Sargassum fusiforme (Hiziki), are all farmed for food.

The microalgae Euglena and Chlorella are being grown successfully on a commercial scale in Japan in freshwater tanks and are being used for both nutritional and biofuel applications.

Farming seaweed
The most important seaweed-producing countries are China, Indonesia and the Philippines. Other significant producers include Korea, Japan, Malaysia, and Zanzibar.

Seaweed is grown in a number of different ways, depending on the species and the climate in which it is grown. It is often seeded onto thin ropes, which can be suspended in deep water using traditional mussel longline techniques, or between bamboo poles in shallow-water. The majority of seaweed species attach themselves to their growing structure with holdfasts, which are highly effective anchors.

No external inputs or feed are needed to grow seaweed, as it converts sunlight to energy through photosynthesis.

One of the exciting benefits of growing seaweed is its ability to sequester carbon dioxide from the oceans, which in turn, reduces atmospheric carbon and ocean acidification. It is estimated that if 9% of the ocean was dedicated to seaweed farming, 53 billion tons of carbon dioxide could be removed from the atmosphere each year. Seaweed also absorbs nitrogen from the oceans, which further helps to reduce ocean acidification.

Impacts of farming seaweed
Due to rapid growth of global seaweed production and its increasing economic importance, the sector is facing many of the same environmental and social challenges experienced by farms and fisheries.

Seaweed farming has been associated with a number of environmental impacts, including changes in water quality, primary and secondary productivity and native fisheries.

The joint ASC-MSC Seaweed Standard is an important tool that addresses these impacts and promotes environmentally sustainable and socially responsible use of seaweed.

Launched in 2017, the standard applies to both farmed and wild-caught seaweed, and requires producers to minimise their impact on the surrounding natural environment, and to manage their operations in a responsible manner, caring for their employees, working with the local community, and being a conscientious neighbour.

Water quality
Seaweed operations must show that they actively minimise their impact on the surrounding natural environment. For example, ASC certified seaweed farmers must not cut down mangroves. As well as damaging natural mangrove forests, this practice negatively affects seaweed farming, by reducing water quality.

Ecosystem
ASC certified seaweed farmers are audited to ensure that productivity can be maintained without affecting the diversity of the local ecosystem on which their activity depends. They must also pay strict attention to waste management and pollution control, energy efficiency, disease and pest management practices, which can all negatively impact on the ecosystem.

Social responsibility
Seaweed operations must also be managed in a socially responsible manner. This means that producers must care for their employees, work with the local community and be good and conscientious neighbours. For example, seaweed farmers must ensure the safety of their workers by ensuring they are protected from harmful practices such as child labour, forced labour or discrimination, and supporting their rights to health and safety, fair and decent wages, and appropriate working conditions.

Uses of cultivated seaweed
Seaweed is consumed as a food, and in a multitude of applications outside the kitchen, including health supplements and drinks, as a natural thickener, in medicines, in feed for fish and livestock, in toothpaste and cosmetics, and as a biofuel. It is also increasingly being used to make textiles and plastic alternatives, including biodegradable packaging, water capsules, and drinking straws.

Cooking and eating seaweed
Seaweed is often referred to as a superfood, because it is rich in iodine and calcium and contains natural antioxidants, minerals and amino acids.  It is a versatile culinary ingredient, with many health benefits, and is attracting a growing health-conscious world population.

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