The habitat-forming capacities of corals have fascinated generations of marine biologists. Shallow-water tropical coral reefs, so often called the ‘rainforests of the sea’, are home to the greatest vertebrate biodiversity on the planet with over 4000 species of reef fish in 179 families estimated to be found in the Indo-Pacific region alone (Myers, 1989). The ability of one species to provide habitat for others has been formalised through the concept of ‘ecological engineering’ (Jones et al., 1994; Wright & Jones, 2006) and we discuss this in relation to cold-water corals and some of their symbiotic associates later in this chapter. Different cold-water coral species develop habitats of varying physical sizes and life spans. For instance, gorgonians may grow close together, forming dense forest-like habitats, but after death these colonies will break down, unlike the reef frameworks left by colonial scleractinians that were discussed in the last chapter.