Seaweed farming, also known as seaweed aquaculture, involves cultivating and harvesting marine algae in controlled aquatic environments. This practice ranges from managing natural seaweed beds to fully controlling the entire life cycle of the crop. It represents a rapidly expanding segment of aquaculture, drawing increasing global attention due to its diverse applications and environmental characteristics.
How Seaweed is Cultivated
Seaweed cultivation begins with “seed” material (young seaweed plants or spores), often sourced from specialized hatcheries. These seeds are then attached to underwater structures. One common technique is the longline system, where ropes, resembling underwater clotheslines, are suspended horizontally between buoys in deeper waters. Seaweed can be tied directly to these ropes, allowing it to grow along the length of the line.
Another common method is the raft system, where seaweed is cultivated on floating structures or frames, often made from bamboo or other durable timber. This allows the seaweed to remain suspended at a consistent depth, typically around 50 centimeters below the surface, optimizing its exposure to sunlight for photosynthesis. For shallower coastal areas, off-bottom or fixed-bottom methods involve driving wooden stakes into the seabed, with lines strung between them to which seaweed is attached. Common types of cultivated seaweed include kelp (Saccharina spp.), nori (Pyropia spp.) used for sushi, and Gracilaria spp., farmed for various food and industrial applications.
Products Derived from Farmed Seaweed
Farmed seaweed has diverse uses, extending far beyond direct consumption. In the food industry, it is a popular ingredient in dishes like sushi, salads, and soups. Beyond whole seaweed, extracts such as carrageenan, agar, and alginate are used for their gelling, thickening, and stabilizing properties in many food products, including dairy items, baked goods, and even chocolate milk. Agar, derived from red algae, is also a long-standing tool for culturing bacteria in scientific research.
Beyond food, seaweed is used in various industrial and agricultural sectors. It is explored for the production of biofuels and bioplastics, offering more sustainable alternatives. Ground seaweed, or seaweed meal, is incorporated into animal feed supplements, improving animal health and reducing methane emissions from livestock. Seaweed is also utilized as a natural fertilizer, either applied directly as compost or processed into liquid extracts, enriching soil with macro and micronutrients and promoting plant growth. Furthermore, its extracts are found in cosmetics as thickeners and in pharmaceuticals as emulsifiers, binders, and for wound care applications, demonstrating its versatile chemical properties.
The Ecological Function of Seaweed Farms
Seaweed farms interact with their surrounding marine environment in several ways. These underwater cultivation sites absorb substantial amounts of carbon dioxide from the seawater as they grow through photosynthesis. This absorption helps reduce dissolved carbon dioxide levels, which can mitigate ocean acidification in the immediate vicinity of the farm. The process also releases oxygen into the water, contributing to the oxygenation of coastal areas.
Seaweed also absorbs excess nutrients like nitrogen and phosphorus that may enter coastal waters from agricultural runoff or wastewater. By taking up these nutrients, seaweed farms can help counteract coastal eutrophication, which can lead to harmful algal blooms and oxygen-depleted “dead zones.” The physical structures of the farms, along with the dense seaweed growth, create complex habitats. These environments serve as nursery grounds and shelters for marine life, enhancing local biodiversity. However, like any large-scale cultivation, unmanaged seaweed farms pose risks like monoculture if diverse species are not cultivated.
Global Scope of Seaweed Aquaculture
Seaweed aquaculture is a global industry, though its production is highly concentrated. Asia remains the dominant producer, accounting for 98% of the world’s farmed seaweed. Countries like China, Indonesia, the Philippines, South Korea, and Japan lead this sector, with commercial farming having been established in Asia over 50 years ago.
While Asia continues to dominate, there is a growing interest and developing industry in other parts of the world. Countries in North America, such as the United States and Canada, along with European nations like France and Norway, are expanding their seaweed farming operations. Despite vast suitable areas, countries like Australia, Russia, Canada, and the U.S. produce less than 1% of global seaweed. The global seaweed cultivation market was valued at $22.45 billion in 2024, with projections indicating rapid growth to $41.23 billion by 2029, highlighting its economic significance.