Pandora Media Inc. (NYSE:P), the online radio that predicts listener music preferences, is down over 16% in trading this morning, on the news that Apple is planning to develop a competing music streaming service. Apple’s potential service would work on its iPhone and iPad, as well as on Mac computers and laptops running Windows, according to the Wall Street Journal. Prior to this news, the Oakland, California-based company was doing well– its shares had grown 26% this year, and it had been able to hold off rivals like Spotify. But it is difficult to compete with the Apple juggernaut.