Over the weekend, a huge swarm of moon jellyfish shut down the 1,400 megawatt Unit 3 reactor at the Oskarshamn nuclear power plant on Sweden’s Baltic Sea coast.  The jellyfish clogged the cooling water intakes, located roughly 60′ feet below the surface of the sea.  They have since been cleared away and engineers are preparing to restart the reactor, but there is no guarantee the jellyfish will not return.  “We hope we have solved the problem regarding the jellyfish, but we are not sure because they can come back,” Anders Osterberg, a spokesman for the operator, Oskarshamns Kraftgrupp AB, said Tuesday.

The Oskarshamn nuclear power facility produces about 10% of the electricity needs of Sweden.  The plant uses the same technology as that of Japan’s Fukushima Daiichi nuclear complex which experienced the worst nuclear disaster since Chernobyl, following the powerful earthquake and tsunami of 2011.

Jellyfish Invasion Paralyzes Swedish Reactor

Is this incident just another sign that jellyfish are taking over the ocean?  In her recent book, “Stung!: On Jellyfish Blooms and the Future of the Ocean“, Lisa-ann Gershwin writes, “Our oceans are becoming increasingly inhospitable to life—growing toxicity and rising temperatures coupled with overfishing have led many marine species to the brink of collapse. And yet there is one creature that is thriving in this seasick environment: the beautiful, dangerous, and now incredibly numerous jellyfish.”

Monsters of the Deep: Jellyfish Threaten the World’s Seas

It isn’t just a problem in the Mediterranean, but worldwide. Especially in late summer, swimmers in the North and Baltic Seas often encounter lion’s mane jellyfish, which are known as “fire jellyfish,” and for good reason. Their stringy stinging tentacles are often the color of flames. Far more common in the region are blooms of milky-blue moon jellyfish, which, like the majority of jellyfish species, do not inflict pain on human beings.

Compass and crystal jellyfish now dominate the coastal waters of Namibia, where sardines were once abundant. And since the mid-1990s, fishermen in the East China Sea and the Yellow Sea have complained that their nets are being filled with more and more jellyfish and fewer and fewer fish.

A species prevalent in Japanese waters could provide the material for a horror film: the giant Nemopilema nomurai, or Nomura’s jellyfish, with a bell diameter of up to two meters (6 feet, 6 inches). In the last century, there were only three population blooms of the species, in 1920, 1958 and 1995. But Japanese scientists report that the Nomura’s jellyfish has invaded Asian waters almost every year since 2002, with only two light years in the interim: 2004 and 2010. The species is so heavy that large numbers caught in nets can capsize fishing vessels.

What does all of this signify? Why are the seas becoming jellified?

[Oceanographer Josep Maria] Gili wrinkles his brow. “The jellyfish are a message in a bottle that the sea is depositing on our beaches,” he says. The ocean’s message to mankind, he adds, is simple: “You are destroying me.”

Not all scientists are convinced that we are facing a jellyfish apocalypse. Some argue that the jellyfish blooms around the world are part of natural cycles in jellyfish populations.

Jellyfish populations might not be exploding after all, suggests Dauphin Island Sea Lab scientist

After a decade or so of somewhat breathless warnings of a jellyfish apocalypse unfolding in the world’s oceans, new research by an international coalition of scientists suggests that the global jellyfish population may be about the same size it always was.

Rob Condon with the Dauphin Island Sea Lab was the lead researcher on a scientific paper published this week by the Global Jellyfish Group, “Recurrent jellyfish blooms are a consequence of global oscillations.”

One of the most fascinating aspects of the research is that the rising phases affect jellyfish all around the globe. Populations rise in all of the world’s oceans at the same time.

“These natural cycles are not uncommon in nature. If you look at cicadas, cicadas are on a 17 year cycle. If you look at tree ring growth, some of the trees have these 18 to 20 year growth spurts,” Condon said. “These cycles are actually quite common. The question now is to understand how human influences on a particular ecosystem may be influencing the natural system.”

Condon said the group’s research shows a rise in jelly numbers in the 1970s, with a much larger rise in jellyfish populations detected in the 1950s. The problem, he said, is the older data are not quite as robust as the more recent data.