Domestic researchers have identified the cause of the increase in seaweed, known as "the uninvited guest of the sea," which damages not only coastal ecosystems but also aquaculture, fishing, and tourism.
The Korea Institute of Ocean Science & Technology (KIOST) announced on the 21st that a research team led by Dr. Seo Seong-bong from the Department of Marine Circulation and Climate Research has identified the cause of the massive influx of Sargassum horneri into Korea's southwestern waters since 2015. The findings were published in the June issue of the international journal Marine Pollution Bulletin.
Sargassum horneri is a type of seaweed from the Sargassum family and is widely distributed in East Asia, including Korea. The organisms drift and live buoyantly, moving hundreds of kilometers offshore from their original habitat due to waves. According to the Ministry of Oceans and Fisheries' statistical environmental information portal "Annual, Regional Collection Statistics of Sargassum horneri," the annual collection volume had been about 300 to 6,000 tons, but around 16,000 tons of Sargassum horneri were collected in Korea's southwestern waters in 2015 and 2021.
To find the cause of the massive influx of Sargassum horneri in certain years, the research team analyzed observational data from the Geostationary Ocean Color Imager 1 (GOCI) and the Geostationary Ocean Color Imager 2B (GOCI-II), as well as a particle tracking model developed by KIOST to analyze migration routes. This model is a numerical model that predicts the movement paths and dispersion areas of marine floating materials by combining physical elements of the ocean, such as ocean currents and winds, and is utilized in tracing studies of marine plastic waste, flood runoff, and radioactive materials.
The research revealed that the main cause of the massive influx of Sargassum horneri into Korea in certain years since 2015 originated from the northern Yellow Sea. In the past, the water temperature in the northern Yellow Sea was low and unsuitable for habitat, but as global warming has increased the water temperature, conditions suitable for habitation have developed. It is believed that Sargassum horneri detached from this area between November and February of the following year moved to the central East China Sea and then to the Korean coastline along ocean currents and the northwestern winter monsoon.
The research team noted that the results of this study will be utilized as important foundational data for establishing a system to scientifically monitor and forecast the influx timing and volume of Sargassum horneri and for preparing rapid response guidelines.
Lee Hee-seung, the head of KIOST, stated, "This research is significant in that it provides a scientific basis for reducing the socio-economic damage caused by the mass influx of Sargassum horneri," adding, "We will continue to analyze the causes of floating seaweed like Sargassum horneri and contribute to establishing a predictable warning system by continuing related research."
References
Marine Pollution Bulletin (2025), DOI: https://doi.org/10.1016/j.marpolbul.2025.117898