The report illustrates two research projects in the framework of HERMES on cold-water coral reefs, which are essential in the balance of many submarine ecosystems: the Tizler reef, located between the Swedish and Norwegian maritime border, is the setting for a study of submarine gardens using a small robot equipped with a camera. Thanks to this little technological gem, researchers at the Tjarno marine biology laboratory are trying to map the precise location, dimensions and shape of the coral reef. These maps will be used in determining fisheries for trawler fishing, which is the main cause of the destruction of reefs. Off the British coast, 15 biologists from six countries are studying the Rockall Bank, a submarine mountain chain, in order to understand the differences between tropical and cold-water corals, notably in terms of how they are nourished.