Seaweed farming, also known as mariculture or kelp farming, involves cultivating and harvesting marine algae in controlled environments. This practice has ancient roots, with cultivation in Japan dating back to the 8th century. Today, it is a rapidly expanding global industry, with a reported world production of over 35 million tonnes in 2019, representing 30% of marine aquaculture. It is gaining increased attention for its capacity to provide sustainable resources and address various environmental challenges.
How Seaweed is Farmed
Cultivating seaweed begins with spore collection from mature plants or through controlled laboratory settings. These spores are nurtured in a nursery phase, often in tanks or protected outdoor systems, until they develop into seedlings. The specific cultivation method depends on the seaweed species and local environmental factors such as water depth, current, and salinity.
Offshore cultivation is a common approach, utilizing systems like long-lines, rafts, or nets. The long-line method suspends ropes horizontally below the surface, anchored to the seabed, allowing seaweed to grow along the lines. Nori cultivation involves nets where spores settle and grow, hung at a depth that exposes the seaweed to air during low tide. Onshore methods, such as tank or pond cultivation, offer a more controlled environment, particularly for species requiring specific water parameters.
Once seedlings are developed, they are outplanted to larger farm structures. Farmers attach the small seaweed pieces to ropes, lines, or nets. Regular monitoring ensures optimal growth and manages potential issues. Harvesting occurs when the seaweed reaches marketable maturity, usually within approximately six months for many species. This can be done manually by cutting the seaweed from the lines or, in larger operations, using mechanical methods.
Applications of Farmed Seaweed
Cultivated seaweed serves a wide array of applications across various industries. A primary use is human consumption, particularly in East Asian cuisines where it is a dietary staple in dishes like soups, snacks, and sushi. Seaweed is also valued for its nutritional content, providing minerals, vitamins, dietary fiber, and flavonoids.
Seaweed plays a significant role in animal feed. In agriculture, extracts are utilized as biofertilizers and biostimulants, enhancing plant growth and nutrient uptake. Compounds like alginates, agar, and carrageenan are widely used in cosmetics and pharmaceuticals for their gelling, thickening, and emulsifying properties. Seaweed is also explored as a sustainable source for biomaterials like bioplastics and packaging, and as a feedstock for biofuels and biogas production.
Ecological Contributions of Seaweed Cultivation
Large-scale seaweed cultivation provides numerous benefits to marine ecosystems and the broader environment. A significant contribution is carbon dioxide absorption, or carbon sequestration. As seaweed grows, it photosynthesizes, converting dissolved CO2 from the ocean into its biomass, and can sequester carbon in marine sediment.
Seaweed farms also contribute to nutrient bioremediation by removing excess nitrogen and phosphorus from coastal waters. These excess nutrients can lead to harmful algal blooms and “dead zones.” By absorbing these nutrients, seaweed helps to improve water quality and restore ecological balance.
Seaweed cultivation can help mitigate localized ocean acidification. As seaweed takes up CO2, it can increase the pH of the surrounding water, providing a buffering effect that benefits calcifying organisms sensitive to acidic conditions. Seaweed farms also create complex three-dimensional habitats, offering refuge, food, and spawning grounds for various marine species, thereby enhancing biodiversity.