Cold-water reefs attract a high diversity of marine fauna and are considered of high ecological importance. High diversity and abundance has been noted at all community levels in and around reefs, from bacteria, to meiofauna and up to the megafauna level. Meio and macrofauna assemblages contain representatives from all the major invertebrate groups: sponges, cnidarians, nematodes, bryozoans, polychaetes, siphunculids; echinoderms, crustaceans and bivalves molluscs (Reed et al., 1982; Rogers, 1999; Richer de Forges et al., 2000; Raes and Vanreusel, 2005; Roberts et al., 2008). Inter specific associations are strong with a high dependence of sessile species upon the structural provisioning and altered hydrodynamics on the reef e.g. sponges and crinoid echinoderms live attached to the corals (Fig.7b); whereas, mobile species e.g. asteroid starfish and nudibranchs, forage across the reef and on the coral polyps (Fig.7a) (Kreiger and Wing, 2002).
The vertebrate fauna of cold-water reefs is rich in density and biomass with numerous species of fish and sharks. This is due to the habitat provisioning services of the reefs (Costello et al., 2005) and the availability of diverse invertebrate assemblages supporting foraging species and high level predators (Reed and Hoskin, 1987). An increasing number of studies are focusing on the vertebrate assemblages of cold-water reefs in light of the threats created by deep-sea fishing. Recent surveys of Lophelia reefs along the southeast coast of the USA, revealed a high abundance of elasmobranchs e.g. carcharhinid ( Carcharhinus altimus), skate (Breviraja claramaculata) and fish such as Nezumia sclerorhynchus and Helicolenus dactylopterus (Fig.7c) (Ross and Quattrini, 2007). On Lopehlia reefs in Norway, species include rock fish (Sebastes spp.), saithe (Pollachus virens) and poor cod (Trisopterus minutus) (Costello et al., 2005).Cold-water coral reefs are the habitat for a number of commercially important species e.g. gag grouper (Mycteroperca microlepis) orange roughy (Hoplostethus atlanticus), cod (Gadus morhua)and observations of high abundances of juveniles and females, suggests a dependence of these species for breeding, foraging and nursery sites (Costello et al., 2005; Fosså et al., 2002;Reed, 2002). D’Onghia et al., (2010) suggest this is the case for the recruitment and spawning of sharks e.g. Etmopterus spinax) and fish (e.g. Mercluccis merluccius and Helicolenus dactylopterus) on Lophelia-Maderpora reefs on the Santa Maria di Leuca Coral Bank, Mediterranean Sea. Debate still remains as to the essential nature of reefs in the life history of deep-sea fish. Some authors suggest that reefs are essential (Fosså et al., 2002)but others disagree (e.g. Auster, 2005).