BIG PINE KEY, Fla. — Nearly 500 divers and snorkelers submerged in the Florida Keys National Marine Sanctuary on Saturday for a "concert" beneath the sea broadcast by a local radio station.The 30th annual Lower Keys Underwater Music Festival, held at Looe Key Reef along the continental United States' only living coral barrier reef, featured four hours of commercial-free music piped below the surface via a series of underwater speakers."We started this as an arts and cultural event 30 years ago (and) thought it would be a one-time thing," said event co-founder and coordinator Bill Becker. "It's the only place we know of where music is put underwater for divers, snorkelers and the marine life."The water-themed playlist included such tunes as the Beatles' "Octopus's Garden" and the themes from Disney's "The Little Mermaid" and television's classic "Flipper." Participants described the music as clear and ethereal, with underwater visibility of about 50 feet.Snorkeler Uli Clef from Munich, Germany, said he was particularly impressed with the vivid colors and tropical fish he saw underwater."I've seen colors from red to blue to white, and even the shades of the sun coming from the water line," Clef said when he surfaced. "All these colorful fishes — that's perfect."Some divers were costumed and pretended to play quirky metal instruments sculpted by Florida Keys artist August Powers. As well as offering an unusual experience for dive and snorkel enthusiasts, the broadcast included diver awareness announcements promoting coral reef protection."We try to get divers to be aware of their impact on the coral reef so that they lessen that impact and this reef can be here for generations to come," said Becker.The event was staged by radio station WWUS in partnership with the Lower Keys Chamber of Commerce.