A Monster Jellyfish Is Threatening Norway's Fjords

The helmet jellyfish. Photo via Flickr user biodivlibrary

Breaking news: A fiendish jellyfish is disturbing the (I assume) otherwise peaceful fauna of the Norwegian fjords. Scientists recently discovered that Beitstadfjord, which is a part of the famous Trondheimsfjord in the very north of Norway, has found its native fish stock annihilated by helmet jellyfish.

Also known as Periphylla periphylla, the jellyfish is most commonly referred to as the “Prince of darkness” because it likes hanging out in dark and deep waters and there's an estimated 40.000 tons of it in just this one fjord. Local media reports that the Beitstadfjord has been “invaded by a monster jellyfish”, which sounds absolutely terrifying, so I called up Biology professor Jarle Mork – whose research acually focuses on fjords – to find out what this all means.   VICE: Hi Jarle. Please tell me, is there any information on why this type of jellyfish has come to Norway?
Jarle Mork: The helmet jellyfish has been recognised in Norway before; back in the 1970s in a fjord outside of Bergen. It seems to have spread from there with the current further north. Right. So what’s going on with other species living in the fjord? Have the jellyfish been consuming them, or have they vanished because the jellyfish eats their food?
The exceptional rise of this jellyfish's population – from about 20,000 tons in 2001 to 40,000 tons in 2014 – has definitely happened at cost of other species in the pelagic ecosystem of Trondheimsfjorden. Periphylla eats the same plankton organisms as young species of other life – particularly the offspring of the economic/ecologic important species in the cod family, such as cod, haddock, whiting, hake, Norway pout, poor cod, ling, and tusk.

As for herring, which has a genetically distinct and native population in Trondhemsfjorden, the helmet jellyfish has been trying to grab their plankton foods all their lives. It’s reasonable to believe, but hard to prove, that the jellyfish’s rise in the fjord has contributed to a current decline in cod, haddock and whiting in the fjord. So in what way is this jellyfish actually affecting other life in the fjord?
The fact that the jellyfish eats pelagic organisms, as well as that it eats fish in their early stages makes it the top predator, in a way. It ultimately eats both the food of its competitors and their offspring. Have similar things happened to sea life creatures in the past?
Well, in Trondheimsfjorden, we’ve seen that edible fish stock – such as cod – has been greatly reduced whenever jellyfish population has increased. However, I must say that the connection between the reduction of cod and the increasing amount of jellyfish is very thin; it’s a quite precarious assumption to point out a connection between the two. There’s also been a slight increase in the temperature along the coast, which has a tendency to mess things up in the eco-balance, too. So what long-term effects can this have?
Well, it is a species that exists naturally in most waters. It may have had similar conditions for breeding before, we don’t know. But we’ve never seen a jellyfish blooming quite like this before. The thing with this jellyfish is that, as apposed to moon jelly or hair jelly, they have a remarkably high capacity of reproduction. So if this actually is the annihilation of man, and the jellyfish are taking over the world, what signs should we be looking out for?
We must have in mind, that this particular species has been found in fossils as old as 550 million years (compared to mankind’s modest 200 thousand years), so it’s not a newbie in the ecosystem. They’ve survived through most of the planet's mass extinctions and have a few properties at hand to positions itself as a top predator. So they’ll probably outlive mankind?
Ha, that just might be the case. I read on Wikipedia that other sea life eats the helmet jellyfish’s faeces. Is that true?
No, except for bacteria and algae, there are barely any forms of life that benefit from eating jellyfish-poop. Thanks, Jarle!