These monster jellyfish have invaded a Norwegian fjord

Its Latin name is Periphylla periphylla.

It's more commonly called the Helmet jellyfish.

And, it's an unwelcome resident of the Trondheimsfjord in Norway.

The fjord now holds an estimated 40,000 tons of these round, red-colored, sea creatures.

And this invasive species is impacting local fishing stocks.

Jarle Mork, a professor and researcher at the Norwegian University of Science and Technology in Trondheim, has been studying the effects of the booming number of jellyfish.

"They are very efficient predators," Mork says. "The population can grow to huge sizes in relatively few years. And they eat the same food as the young stages of the commercial fishes. And in addition they eat small and young stages of those competitors."

Mork says that the jellyfish are harming commercial species like cod, haddock, whiting and hake.

Periphylla periphylla usually lives at depths of 3,000 feet but began invading the shallow waters of the fjords in the 1970's.

"These creatures, they don’t like light so they are deep dwelling," says Mork. "They only come to the surface at the darkest of the night."

The jelly invasion is causing headaches for fishermen but the jellyfish pose no threat to swimmers.

"You can swim without any danger," Mork says. "It is not seen in the surface layers [of the water]. In addition, it’s not as poisonous as other jellies which also occupy Norwegian waters in summer."

Mork says that researchers are looking into ways to capitalize on the high number of fjord jellies. One possibility is using the jellyfish's collagen for cosmetics.

Its Latin name is Periphylla periphylla.

It's more commonly called the Helmet jellyfish.

And, it's an unwelcome resident of the Trondheimsfjord in Norway.

The fjord now holds an estimated 40,000 tons of these round, red-colored, sea creatures.

And this invasive species is impacting local fishing stocks.

Jarle Mork, a professor and researcher at the Norwegian University of Science and Technology in Trondheim, has been studying the effects of the booming number of jellyfish.

"They are very efficient predators," Mork says. "The population can grow to huge sizes in relatively few years. And they eat the same food as the young stages of the commercial fishes. And in addition they eat small and young stages of those competitors."

Mork says that the jellyfish are harming commercial species like cod, haddock, whiting and hake.

Periphylla periphylla usually lives at depths of 3,000 feet but began invading the shallow waters of the fjords in the 1970's.

"These creatures, they don’t like light so they are deep dwelling," says Mork. "They only come to the surface at the darkest of the night."

The jelly invasion is causing headaches for fishermen but the jellyfish pose no threat to swimmers.

"You can swim without any danger," Mork says. "It is not seen in the surface layers [of the water]. In addition, it’s not as poisonous as other jellies which also occupy Norwegian waters in summer."

Mork says that researchers are looking into ways to capitalize on the high number of fjord jellies. One possibility is using the jellyfish's collagen for cosmetics.