U.S. News - Diablo Canyon nuclear plant in California knocked offline by jellyfish-like creatures called salp Diablo Canyon Power Plant / AP This photo provided by the Diablo Canyon Power Plant on Friday shows salp, a gelatinous sea creature, at a nuclear reactor intake structure. 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 msnbc.com 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. Salps are tiny, gelatinous organisms that move by contracting, thus pumping water throughout their bodies. They can reproduce and multiply quickly, and are most common in equatorial, temperate and cold seas. Salps do not usually appear at the coast. "Ordinarily they live further out at sea," Larry Madin, a salp expert and research director at Woods Hole Oceanographic Institution in Massachusetts, told the Los Angeles Times. It sounds like these were brought in on a current or blown in by wind. Madin said the slimy swarm at Diablo would probably go away in a few days. "They're harmless - they don't sting - but they're not too good for power plants," he told the Times. Despite the 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 Times. Similar problems have cropped up at nuclear plants in the U.S., Japan, Israel and Scotland over the years, the newspaper said. It's something you would expect along the coast," Uselding said.