A small but potentially dangerous jellyfish species, native to the Pacific Ocean, has been found in Danish waters for the first time. While its sting can cause allergic shock, experts say the risk of encountering it remains extremely low.
Toxic Pacific Jellyfish Found in Danish Waters
Biologists at Denmark’s Øresund Aquarium have made an unusual find: a jellyfish species called Gonionemus vertens, better known in Danish as the “sticky jellyfish,” has been discovered in the Øresund strait between Denmark and Sweden. The small and highly venomous species is originally native to the Pacific Ocean but has previously been detected in limited areas of Norway and on Sweden’s west coast. The jellyfish is usually found in Pacific Oceans, which makes this case interesting.
The jellyfish, typically measuring just 2 to 3 centimeters (less than 1.2 inches), was accidentally discovered when aquarium staff were collecting larger jellyfish for research. One of the Gonionemus vertens had latched onto a common jellyfish and was only noticed once the specimen had been brought into the aquarium’s tanks. It’s size makes it harder to spot than the normal jellyfish, so it’s good to be aware of when swimming at the beach.
Highly Toxic Sting with Severe Reactions
Despite its small size and nearly transparent body which makes it difficult to spot underwater, the jellyfish poses a health concern. It contains powerful venom in its tentacle cells—more potent than the larger jellyfish species commonly found in Danish waters, such as the moon jellyfish or lion’s mane jellyfish.
People who accidentally come into contact with this species have reported effects ranging from skin irritation and local pain to more severe symptoms such as breathing difficulties, muscle soreness, exhaustion, and in extreme cases, anaphylactic shock. These reports originate primarily from regions such as Japan and the Pacific Northwest, where the jellyfish is more commonly observed.
Few Sightings, Minimal Risk for Swimmers
Although one specimen has been confirmed found in Danish waters, marine experts are emphasizing that there’s no reason for the public to panic or avoid swimming in the Øresund strait. The discovery appears to be an isolated incident, and only a handful of sightings have been documented across Scandinavia to date.
The jellyfish likely arrived via ballast water—seawater taken into cargo ships for stability and later released at other ports. This is a well-known pathway for marine species to travel long distances and enter non-native ecosystems. However, its survival in Øresund is not surprising, as the area features both saltwater and brackish conditions, which align with the jellyfish’s preferred environment.
Monitoring is Underway
While there is little cause for concern at the moment, marine biologists are keeping a close watch for further sightings. Continued monitoring will help determine whether the species is an isolated occurrence or part of a broader trend.
With competition for food already high among jellyfish species found in Danish waters, biologists say it is unlikely that Gonionemus vertens will proliferate rapidly. Still, its presence marks yet another example of marine species shifting their habitats, sometimes due to climate change, global trade, or changes in water temperature and salinity.
How to Stay Safe
Should swimmers notice a small, reddish-orange jellyfish roughly the size of a bottle cap, they are advised not to touch it. The jellyfish’s tentacles can still sting even if detached or seemingly motionless.
From a distance, Gonionemus vertens has a distinctive look—a round, transparent bell with orange markings and sticky-looking tentacles extending underneath. It’s this adhesive quality that gives it its nickname in Danish, as it tends to cling to seaweed and even other jellyfish.
Conclusion
This first-time discovery of a Pacific jellyfish in Øresund highlights the evolving dynamics of marine ecosystems and the subtle risks posed by non-native species. While the “sticky jellyfish” may cause concern due to its toxicity, minimal sightings and expert reassurance indicate that swimming in Danish waters remains safe. Authorities and scientists will continue to monitor the situation closely to ensure both public safety and ecological balance.
