IE 11 is not supported. For an optimal experience visit our site on another browser.

Diablo Canyon nuclear plant in California knocked offline by jellyfish-like creature called salp

This photo provided by the Diablo Canyon Power Plant on Friday shows salp, a gelatinous sea creature, at a nuclear reactor intake structure.
This photo provided by the Diablo Canyon Power Plant on Friday shows salp, a gelatinous sea creature, at a nuclear reactor intake structure.Diablo Canyon Power Plant / AP

In Japan, it was a monstrous earthquake and tsunami that brought down the Fukushima nuclear plant. In California, it’s a tiny, jellyfish-like sea creature called salp that’s causing problems at the Diablo Canyon atomic plant.

An invasion of salp has prompted Pacific Gas and Electric Co. to temporarily shut down a nuclear reactor at Diablo Canyon, in Avila Beach, San Luisa Obispo County, on the central California coast.

A giant swarm of the transluscent barrel-shaped organisms this week clogged intake screens that are used to keep marine life out of the seawater that is used as a coolant for the nuclear plant.

On Wednesday, PG&E officials reduced power output at the Unit 2 reactor, then decided to shut it down altogether “until conditions improve at the intake structure.” The plant’s other reactor, Unit 1, had already been shut down earlier in the week for a planned refueling and maintenance outage.

“Safety being the number one priority, there was such an influx of salp and you need ocean water to cool the reactors,” PG&E spokesman Tom Cuddy told on Friday. “At that point we made a conservative decision to safely shut down the unit.”

PG&E owns and operates the Diablo Canyon Power Plant, whose two reactors together produce approximately 2,300 net megawatts of electricity – enough to serve nearly 3 million northern and central California homes.

Cuddy said he wasn’t sure when the Unit 1 reactor would come back online.

“We’ll turn the unit on to full power when it’s safe to do so – when the salps leave,” he said. “The bottom line is we’re taking a methodical and conservative approach.”

Lara Uselding, a spokeswoman for the Nuclear Regulatory Commission, the federal agency that oversees reactor safety and security, said the plant is not in any danger.

“It’s not a normal operation condition, but the plant is safe and all the systems operated as designed,” she said.

Watch US News videos on

Salps are tiny, gelatinous organisms that move by contracting, thus pumping water throughout their bodies. They can reproduce and multiply quickly.

Though salps look a bit like jellyfish, they are actually more closely related to organisms that have backbones. They typically grow to 1 or 2 inches long and usually do not appear at the coast, says Larry Madin, a salp expert and research director at Woods Hole Oceanographic Institution in Massachusetts.

“They’re typically more of an offshore living organism," Madin says. He surmises that the swarm at Diablo may have been carried in on currents blown by wind.

But Steve Haddock, a scientist with the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., said salps have been blooming in high numbers along the California coast since at least December. Several sightings have been reported to JellyWatch, a website Haddock runs to track sightings of jellyfish and other marine organisms.

Other than clogging the cooling system filters of a nuclear plant, the organisms pose no danger, says Bruce Robison, senior scientist at the Monterey Bay Aquarium Research Institute. They don’t sting, they don’t have teeth and they’re not poisonous.

Salps passively feed off tiny organic particles in the water and can reproduce sexually or asexually. “They can have their population size expand tremendously within a short period of time, which makes them very abundant. In a small space, they can take up all the space,” Robison says.

Madin said the slimy swarm at Diablo would probably go away in a few days, carried off by currents. Or, says Robison, they’ll quickly die off when their food supply runs out.

So the best bet, experts say, is for nuclear officials to just wait it out in the short term. "Long term, perhaps if their intakes were a bit deeper, it would not be a problem," Haddock said.

Despite the reactor outage, California is not expected to experience any electricity shortages because it has ample reserves, said Stephanie McCorkle, spokeswoman California ISO, which operates the state's power grid and wholesale markets.

It’s not the first time that sea creatures have interfered with nuclear plant activity.

In 2008, a swarm of jellyfish led to a sharp decrease in power generation at Diablo Canyon, according to the Los Angeles Times.  Similar jellyfish problems have cropped up at nuclear plants in the U.S., Japan, Israel and Scotland over the years, the newspaper said.

“It happens. It’s something you would expect along the coast,” Uselding said.

Madin said this is the first time he’s heard of salps interfering with the operation of a nuclear plant.

 More content from and NBC News:

Follow US News on on Twitter and Facebook