Seaweeds are macroscopic algae that grow in the marine and shallow coastal waters and on
rocky shores. They’re a renewable source of food, energy, chemicals and medicines. They’re also termed as the ‘Medical Food of the 21st Century’ as they are being used as laxatives, for making pharmaceutical capsules that is used in treatment of goiter, cancer, bone-replacement therapy and in cardiovascular surgeries.
They are also used as a source of agar, agarose and carrageenan that are used in laboratories, pharmaceuticals, cosmetics, cardboard, paper, paint and processed foods.
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Global Leaders In Seaweed Farming
Seaweed production is led by China, the world’s largest producer, followed by Indonesia, the Philippines, and South Korea. There’s been a surge of interest in India, where coastal regions are being tapped for their potential. European countries like Norway, Ireland, and France are also investing in cold-water species.
Economic Benefits
If we look at various trusted sources, we can notice that in Indonesia, farmers in Southeast Sulawesi earn an average of USD 800–2,700 per year from seaweed. While in Philippines, seaweed farming returns are exceptionally high, 93% ROI using raft culture and up to 243% ROI using bottom-line methods. (FAO)
Cultivation of seaweed requires minimal capital and labor, this makes it suitable for low-income coastal communities. Fast-growing species like Kappaphycus alvarezii mature in 45–60 days due to which farmers can harvest 4 to 6 times a year.
| Country | Avg. Income/Year | ROI (%) | Harvests/Year | Notable Crop |
|---|---|---|---|---|
| Indonesia | $800–$2,700 | 150–240% | 6 | Kappaphycus, Gracilaria |
| Philippines | $1,000–$3,000 | 93–243% | 5–6 | Eucheuma spp. |
| India (Tamil Nadu) | ₹1.5–2 Lakh ($1,800–$2,400) |
~200% | 5–6 | Kappaphycus alvarezii |
| Kenya / Tanzania | Community-based | N/A | 5–6 | Spinosum, Cottonii |
The global seaweed market size was valued at USD 9.01 Billion in 2024 and is projected to grow at a CAGR of 8.17% from 2025 to 2033.
Environmental Benefits
Seaweed can absorb CO₂ up to 50 times faster than land plants. You will be surprised to know that 1 hectare of seaweed can capture up to 1,500–2,000 kg of CO₂ per year. It helps to lower ocean acidity, and restore marine ecosystems. Seaweeds also act as habitats and breeding grounds for fish, crabs, and mollusks, therefore helps to promote ecological balance and boost local marine fish stocks.
Unlike traditional crop farming, seaweed cultivation requires no irrigation, no land clearing, and no chemical inputs, that makes it one of the most sustainable crops in the world. They also absorb excess nitrogen and phosphorus from water and prevent harmful algal blooms and eutrophication.
How Seaweed Is Cultivated
Farmers can cultivate seaweed in shallow coastal waters of maritime states by using Bamboo-Rafts or Tube-Nets. So, if you want to cultivate seaweed, you have to start by selecting a suitable location. Here is how you can do that:
- Stable seawater with not less than 30 ppt salinity,
- Sandy or rocky bottom with transparent water,
- Ideal temperature: 26-30o Celsius.
- The area should have minimum 1.0 m water depth during low tide.
- Area with mild water currents are preferred.
Raft Preparation
Prepare 3×3 m raft made of bamboo poles having 7.5 to 10 cm diameter. Floating line culture systems can be used for seaweed cultivation in calm, shallow coastal waters. To prepare a raft you will need to have: 4 long poles (3 m each) + 4 short poles (for cross-bracing), nylon rope or coir rope, empty sealed plastic bottles of 2–4 L for buoyancy, anchor stones or concrete blocks, and seaweed planting material.
Seaweed Varieties For Cultivation
| Scientific Name | Common Use | Cultivation Suitability |
|---|---|---|
| Kappaphycus alvarezii | Source of carrageenan (thickener) | Widely cultivated on floating bamboo rafts in India, Philippines, Indonesia |
| Gracilaria edulis | Used for agar extraction, animal feed | Grown on tube nets and floating rafts in coastal India |
| Gracilaria dura | Agar production, biostimulants | Suitable for floating structures; used in Indian coastal waters |
| Eucheuma denticulatum | Carrageenan production | Grown using raft systems in East Africa and Southeast Asia |
Management
To get good yield, keep inspecting your rafts. Clean the culture lines to remove epiphytes, barnacles, and algae overgrowth. Remove pest species like fish, sea urchins, or turtles.
Harvesting Of Seaweed
Seaweed gets ready for harvesting 45 to 60 days after planting, depending on the species and environmental conditions. To harvest seaweed you can cut mature seaweed from the culture lines using knives or scissors and 10–15% of the part for regeneration. After harvesting, rinse with clean seawater to remove sand, debris, and biofouling. Sun-dry seaweed on clean tarpaulin or drying racks for 2–3 days until moisture content is reduced to less than 20%.
Thereafter, store in cool, dry, and ventilated space.
Yield Of Seaweed
Farmers can expect around 200 Kilograms per raft, it may vary from species to species.
That’s why cultivating seaweed is not only economical and sustainable, but also easy and less time consuming. If you’re a farmer living in coastal areas, then starting seaweed cultivation can have positive impact on your livelihood.
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