GoPro's stock price declined sharply after an Apple patent filing revealed the tech giant may enter GoPro's action camera market. The patent described a remote-controlled camera system similar to GoPro's offerings. This news erased $880 million from GoPro's market value in just six and a half hours as investors feared increased competition from Apple. GoPro has seen huge revenue growth recently but some feel its high valuation makes it vulnerable if growth slows or competitors intensify.