Asked by: Richard Cassidy, Manchester
In the tropics, it was long thought that corals build reefs only in shallow waters, down to around 40m. These microscopic creatures have algae living inside them that need sunlight to photosynthesise. Lately, using new and improved diving equipment, scientists are discovering much deeper corals living in the ‘twilight zone’ down to 160m, even though very little sunlight trickles that far down. It’s possible these deep corals could help recolonise shallower reefs damaged by impacts like coral bleaching. Other types of coral – without algae partners – live around the world, thousands of metres beneath the waves.