KIOST develops high-density seaweed farming technology that doubles output and absorbs CO2

South Korean researchers have developed a new aquaculture technique that more than doubles the productivity of seaweed such as kelp and sea mustard while absorbing large quantities of carbon dioxide from the ocean.

The Korea Institute of Ocean Science and Technology (KIOST) announced Tuesday that it has developed a high-density "longline suspension" farming method capable of increasing seaweed output by up to twice that of conventional techniques. The method uses vertical space rather than expanding horizontal coverage, significantly raising production per unit area and offering a new model for large-scale seaweed cultivation.

Coastal fishing communities in South Korea have long relied on the conventional longline method, in which sea mustard and kelp are grown along horizontally extended ropes. While that approach reduces exposure to tidal flat sediment and contamination, large-scale installations can obstruct vessel navigation and make inefficient use of available sea space.

KIOST's longline suspension method addresses those constraints by hanging 3-meter vertical ropes called "suspension lines" at 1-meter intervals from a 200-meter horizontal mainline. Seed strings carrying juvenile seaweed are wound around each suspension line. The technique — adapted from longline suspension systems already used in oyster and sea squirt farming — dramatically increases cultivation density without expanding the horizontal footprint.

The system is also built for durability. The ropes are made from polypropylene at least 20 millimeters in diameter, chosen for its resistance to corrosion and decay, its light weight, and its low raw-material cost. To prevent the suspension lines from tangling or twisting, a secondary mainline and anchor weights are installed at the bottom, and metal spacers are placed every 50 meters to maintain consistent spacing between the upper and lower lines, keeping the structure intact against strong currents and waves.

Field trials were conducted in the waters off Tongyeong, South Gyeongsang Province, home to KIOST's Tongyeong Maritime Demonstration Base, using sea mustard and kelp as test crops. Measuring average output across the upper, middle, and lower sections of a 3-meter suspension line yielded 12.11 kilograms per meter at the top, 8.29 kilograms per meter in the middle, and 7.78 kilograms per meter at the bottom — a combined total of 28.18 kilograms per suspension line. Output over a 200-meter stretch reached approximately 5.6 tons, compared with roughly 3 tons per 200 meters recorded by conventional longline farmers in Wando, South Jeolla Province, and about 2 tons in Gijang, Busan — 1.9 times and 2.8 times higher, respectively, based on field surveys of local fishers.

The productivity gains carry significance beyond economics. Unlike land plants, which absorb carbon dioxide from the air, seaweed takes in dissolved CO2 through its entire body. Kelp in particular absorbs carbon at more than twice the rate of tropical rainforests. Because seaweed grows quickly and can be harvested and replanted every year, scaling up cultivation directly expands the ocean's carbon absorption capacity.

"Seaweed is not only a next-generation blue carbon resource but also a strategic asset that can simultaneously drive marine ecosystem recovery, raise fishing community incomes, and create high-value industries," KIOST President Lee Hee-seung said. "We will use science and technology to enhance the productivity and utilization value of seaweed, and develop sustainable solutions for marine and fisheries resources in the era of carbon neutrality."