The helicopter was on a 14 CFR Part 135 air tour operation with a pilot and six passengers aboard. It was flying parallel to the shoreline when a complete loss of engine power occurred. The pilot performed an autorotation to the water about 150 feet from a cliff shoreline. The helicopter was not equipped with floats. All occupants exited the helicopter uninjured as it was sinking. Life vests were aboard the helicopter, but were not worn by the occupants. Three of the passengers managed to climb onto rocks and were eventually rescued by helicopter. They indicated that they had not been briefed that life preservers were aboard the helicopter. The other four occupants were unable to climb onto rocks along the shore. One of these, a passenger, was rescued by personnel of a boat. The pilot and the other two passengers drowned. The helicopter was recovered from the ocean. An examination and tests of components revealed the internal drive splines of the engine-driven fuel pump (MFP-261) had worn to the point of slippage. This failure would have resulted in a total loss of engine power.