Bottom trawling is often singled out by scientists and activists as one of the world's most destructive fishing techniques. It's prevalent in European waters. Nothing escapes the vast nets: fish, crustaceans, but also coral reefs and seagrass beds. Wherever trawlers go, the ocean floor turns into a desert. In this edition of Down to Earth we head to Spain, where bottom trawling is rife, even in marine protected areas.