Barbed wire jellyfish season begins with fewer sightings reported.
Researchers at Norway’s Institute of Marine Research (Havforskningsinstituttet) report that the seasonal appearance of the barbed wire jellyfish (Apolemia sp.) has begun, though early observations suggest fewer sightings than at the same time last year.
Marine scientist Tone Falkenhaug said the species has so far been recorded in Troms and West Finnmark, but numbers remain low. “There have been fewer observations so far than at the same point last year and the year before,” she said.
The colonial jellyfish, which forms long chains of individual organisms and delivers a powerful sting, has previously caused damage to farmed fish. In 2023, a mass occurrence was believed to have led to the deaths of about three million salmon, according to the Institute’s risk assessment report. It was the first large-scale outbreak in more than 20 years to cause significant losses for Norway’s aquaculture sector.
Data from the citizen science platform Dugnad for havet indicate a consistent seasonal pattern, with the barbed wire jellyfish typically appearing from September through January, peaking in November. Since 2019, more than 2,000 reports of the species have been logged along the Norwegian coast, with a record number in 2023.
Researchers are continuing to investigate where the jellyfish originate and why occurrences have increased in recent years. One leading hypothesis is that the species arrives with Atlantic water inflows.
“There are several indications that the jellyfish are transported toward the Norwegian coast,” Falkenhaug said. Preliminary modelling by Jon Albretsen supports this theory, showing that simulated jellyfish particles released west of Scotland in February and March align closely with later observations along the coast.
The findings strengthen the hypothesis that Atlantic inflow via the Faroe–Shetland Channel is the main route bringing the barbed wire jellyfish into Norwegian waters.
