Emiliania huxleyi bloom south of Cornwall (UK)
Under certain conditions, Emiliania huxleyi can form massive blooms which can be detected by satellite remote sensing. What looks like white clouds in the water, is in fact the reflected light from billions of coccoliths floating in the water-column.

Details: Landsat image from 24th July 1999, courtesy of Steve Groom, Plymouth Marine Laboratories. This bloom attracted considerable coverage in the UK media.