A massive swarm of jellyfish clogged a water intake pipe at the Oskarshamn power plant in Sweden, forcing operators to temporarily shut down the reactor. The Oskarshamn plant on the Baltic Sea coast of southeastern Sweden is the world's largest boiling-water reactor, producing 1,400 megawatts of output.
A spokesman for the plant, Andres Osterberg, told the New York Times that the jellyfish had been cleared out by Tuesday, and that they are preparing to restart the reactor. However, this may only be a temporary fix:
“We hope we have solved the problem regarding the jellyfish, but we are not sure because they can come back,” Mr. Osterberg said by phone. The species is known as the common moon jellyfish, a resilient type that can sting, but it is generally not dangerous to humans.
The moon jellyfish, which can grow as big as 15 inches in diameter, entered the pipes about 60 feet below the water's surface. Cold water from these pipes is used to cool the reactor and turbine systems. Osterberg said they were likely to have been killed by the plant's water filtration systems, and that there was no risk of a nuclear accident.
This is not the first time a nuclear plant has been affected by clouds of jellyfish, because the reactors are often build on or near large bodies of water. In fact, Oskarshamn was forced to shut down one of its reactors in 2005 because of a similar invasion. In 2011, the creatures took down a power plant in the UK.
Although there has been a number of dramatic jellyfish blooms in recent years, ocean scientists debate whether or not the total population is growing. A report last year from the Global Jellyfish Group argued that there's not enough historical evidence to know if the jellyfish population is experiencing growth.
What is clear, however, is that in changing ocean environments, jellyfish seem well-suited for survival. Lene Moller, a researcher at the Swedish Institute for the Marine Environment, told NPR that although she agrees that there's not enough data to know if jellyfish blooms are more common, they can thrive in extreme environments:
"It's one of the species that can bloom in extreme areas that . . . are overfished or have bad conditions," said Moller. "The moon jelly likes these types of waters. They don't care if there are algae blooms, they don't care if the oxygen concentration is low. The fish leave . . . and (the moon jelly) can really take over the ecosystem."