Vast areas of the ocean are getting darker, according to research based on satellite imaging. Marine ecosystems are governed by faint light changes – from mass nightly migrations to coral spawning cycles – so what happens when that light begins to fade? Ian Sample talks to Prof Tim Smyth from the Plymouth Marine Laboratory about why this darkening is happening and how life in the ‘photic zone’ – the sunlit upper layer that is home to 90% of marine organisms – could be profoundly affected Planet’s darkening oceans pose threat to marine life, scientists say. Help support our independent journalism at theguardian.com/sciencepod