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Over 100 observations of string jellyfish reported


This colonial jellyfish can reach lengths of up to 30 metres.

Photo: Erling Svensen / IMR

This autumn there has been a big increase in the number of string jellyfish along the coast. This colonial jellyfish can reach lengths of up to 30 metres and it can be fatal to farmed fish.

Through the Marine Citizen Science portal (Dugnad for havet), members of the public can report any interesting things they observe along the coast. So far this year, 110 observations of string jellyfish have been reported.

“But the big increase in reports only began in September–October”, says marine scientist Tone Falkenhaug.

From Oslofjorden to Troms

This is the same situation as we saw last autumn.

“Of the past 20 years, only last year had similarly high levels to this year”, says Falkenhaug. 

The string jellyfish is an Atlantic species, and the researchers believe that it comes to the coast with inflows of Atlantic waters. 

“We have received reports of observations along the whole coast, from Oslofjorden all the way up to Troms. Over the past week, we have received most reports from Trøndelag”, she says. 

Like other jellyfish, string jellyfish can appear very suddenly, and then disappear for a number of years. 

Many farmed fish were killed in 1997 and 2001

The string jellyfish is a colonial jellyfish that can reach lengths of up to 30 metres. Within the colony, individuals have different roles. The ones whose job is to catch food or defend the colony have stinging cells. 

“This means they may sting and cause harm to farmed fish”, says Falkenhaug. 

If a colony hits a cage, it gets broken up, and small bits of jellyfish, including the stinging cells, may enter the cages. 

On two previous occasions, string jellyfish have caused mass mortality events at fish farms. In 1997, jellyfish killed 12 tonnes of salmon, while 600 tonnes of fish died in 2001. 

“That’s why we try to keep an eye on this species of jellyfish”, explains Falkenhaug. 

Smilende kvinne med sjø og solskinn i bakgrunnen.
Jellyfish are difficult animals to study because they are made of jelly-like matter that break up so easily, explains Tone Falkenhaug. (Photo: Erlend Astad Lorentzen / IMR)

Researchers need YOUR help

However, doing that is not so easy, because jellyfish are difficult animals to study. 

“That is mainly because they are made of jelly-like matter. That makes jellyfish hard to catch using normal gear, because they break up so easily”, says Falkenhaug. 

That’s why marine scientists need help from the general public. 

“The Marine Citizen Science portal is a good tool. In addition, we have received great help from divers, as well as from the aquaculture industry, which has spotted these jellyfish in the vicinity of their farms”, she says. 

In short: if you see a string jellyfish, report your observation to the Marine Citizen Science portal.