SEOUL: As South Korea enters the height of summer, warming seas are bringing an unwelcome visitor to its coasts: jellyfish.
Marine experts say rising water temperatures are driving a sharp increase in venomous jellyfish, posing growing risks not only to beachgoers but also to fishermen and coastal industries.
The greatest concern is Nomura’s jellyfish (pic), one of the world’s largest jellyfish species that usually originates off the coast of China and drifts into South Korean waters on ocean currents.
It can grow up to 2m in diameter and weigh as much as 200kg, with tentacles capable of delivering painful stings.
According to a report released last week by the National Institute of Fisheries Science (NIFS), the appearance rate of Nomura’s jellyfish rose from 2.9 per cent on June 18 to 11.4 per cent by July 2, indicating the species is spreading rapidly in South Korean waters.
The appearance rate was the highest around the southern island of Jeju, reaching 80 per cent so far this year, up from 36 per cent in 2016. In other words, eight in 10 fisheries monitoring personnel in the region reported spotting Nomura’s jellyfish.
While swimmers face the risk of painful stings, the impact extends well beyond beaches. Large jellyfish can clog fishing nets, damage catches and increase costs for fishermen.
Scientists attribute the increase to warmer ocean temperatures, which create more favourable conditions for jellyfish to survive and spread.
The warming seas are also drawing more sharks into coastal waters.
On July 4, residents in Gangneung, Gangwon province, received an emergency phone alert after sharks were spotted about 4km east of Anmok Beach.
The Gangneung Coast Guard said sharks had been sighted near both Anmok and Gyeongpo beaches, prompting city officials to advise caution for swimmers, divers and other marine leisure activities.
According to the NIFS, 46 large sharks had been reported in South Korean waters as at June 24, nearly four times the 12 recorded during the same period in 2025.
The authorities in several coastal regions have stepped up precautions against jellyfish and sharks.
Measures include installing offshore safety nets at popular beaches to keep large marine animals away from swimmers, while officials are urging beachgoers and fishermen to closely monitor local advisories throughout the summer. - The Korea Herald/ANN
