Jellyfish smothered the sea water cooling system at a Japanese nuclear power plant on Wednesday, forcing operators to cut output by nearly 30 per cent, officials said. Countless translucent jellyfish choked up sea water intakes at Kashiwazaki Kariwa Nuclear Power Plant in Niigata, North of Tokyo, said a spokesman for the operator, Tokyo Electirc Power Ltd."This the first time jellyfish have caused a power reduction at the nuclear plant," the spokesman said.