Highly venomous large jellyfish are appearing earlier and in greater numbers than in previous years due to climate change. With crowds flocking to beaches nationwide amid the heat wave, caution is required.
Nomura's Jellyfish Appearance Rate Doubles in a Decade
According to nationwide jellyfish monitoring results from the National Institute of Fisheries Science released Tuesday, the appearance rate of Nomura's jellyfish in waters off Jeju during the first week of July jumped from 36% in 2016 to 80% this year, more than doubling over the decade. This marks a sharp increase even compared with the appearance rate during the same period last year (55.6%). In addition to Jeju, the jellyfish have also been detected at low densities in waters off South Jeolla, South Gyeongsang, and Busan.
Originating along China's coast and carried into Korean waters by ocean currents, this jellyfish is a super-large species that can grow up to 2 meters in diameter and weigh as much as 200 kilograms. It is considered the most concerning species, as merely touching its venomous tentacles can threaten one's health.
In response, the institute issued a preliminary jellyfish advisory for waters off Jeju on May 22, and the Ministry of Oceans and Fisheries raised its crisis alert level from "caution" to "warning" on the 8th of last month. Last year, the special advisory was first issued only on June 4, meaning this year's warning came about 10 days earlier.
Rising water temperatures around the Korean Peninsula have been cited as the reason for the early appearance of jellyfish. Analysts say that as water temperatures during March and April, when jellyfish larvae emerge, remained higher than in previous years, plankton—their food source—increased and their growth rate accelerated. In addition, with ocean currents along China's coast growing stronger, Nomura's jellyfish appear to have been observed more frequently than last year.
The problem is that water temperatures are likely to rise even further this summer. The oceans ministry forecast that water temperatures in Korean waters this year will be 1.2 to 2.8 degrees higher than normal, while the Korea Meteorological Administration put the probability of sea surface temperatures exceeding normal levels from July to September at 50 to 70%. As water temperatures rise, the reproduction of highly venomous species such as the curtain jellyfish and the moon jellyfish could increase, raising the likelihood of unfamiliar species entering Korean waters, such as the tropical Portuguese man o' war that appeared off Jeju last month.
Evacuate If Spotted, Rinse With Seawater If Stung
According to the Jeju Fire and Safety Headquarters, emergency dispatches related to jellyfish stings fell from 32 cases in 2021 to 11 cases in 2024, then rose again to 19 cases last year. Nationwide jellyfish sting incidents reached 2,039 last year, with one person recorded as having died.
When stung, victims experience pain, itching, burning, and redness, along with a whip-shaped rash, which may be followed by fever, chills, vomiting, and muscle pain. In severe cases, it can lead to difficulty breathing or nerve paralysis, and in the worst cases, death from anaphylaxis, requiring particular vigilance. Since small children can suffer fatal injuries from even a small amount of venom, careful observation by guardians is required.
If a jellyfish is spotted, one should immediately leave the area, get out of the water, and notify a lifeguard. On the beach, wearing shoes is safer than going barefoot, and it is best not to touch even dead jellyfish with bare hands.
Rinsing with tap water or bottled water when stung is cited as a typical incorrect response. This is because when fresh water or alcohol contacts the skin, osmotic pressure can stimulate remaining nematocysts and release more venom. Spraying vinegar or alcohol is also prohibited.
The safest method is to thoroughly rinse the wound with seawater or saline solution. If tentacles remain, they should be carefully removed with tweezers or a plastic card such as a credit card, and rubbing or wrapping with a compression bandage should be avoided. If pain is severe or symptoms such as nausea, vomiting, headache, cold sweat, or fainting appear, one should immediately call 119 and seek a hospital. Children, the elderly, pregnant women, and those with underlying conditions should seek medical attention even if symptoms are mild.
