Across the world 4,200 species of cold-water corals have been recorded, lack of funding and expertise have left large areas of the worlds oceans unmapped. These un-investigated areas have the potential to be as rich in diversity as the cold-water corals already discovered (URL 1).
Cold-water coral reefs provide structures with a multitude of micro-habitats for many species to occupy. They play a vital role in fisheries: acting as a haven for juvenile fish and crustaceans (URL 1). In Norway 850 species where found living on one Lophelia reef providing a habitat and foraging area to a variety of fish such as Atlantic Mackeral, Monkfish and species of Gurnard (URL 1) (Figure 15).  Tropical coral reefs are often said to be the rain forests of the sea, but it is clear that the diversity of life created by cold-water corals is just as significant. 

Figure 15: a) the Alfonsino b) the Blackberry Rosefish c) the Gadiform d) the Roughtip Grenadier all found on Lophelia pertusa reef. (Image replicated from Roberts et al. 2009)

 The habitats created by cold-water corals vary in longevity and size (Roberts et al. 2009). Gorogorians can form dense forest like habitats but colonies quickly break down after death. Whereas Scleractinians and Black corals can provide a structural habitat before and after their lifetime (Roberts et al. 2009).
The Christmas Tree Coral Antipathes dendrochristos (Figure 16) has recently been discovered to harbour an amazing display of invertebrates; the epifauna hang from its branches like ornaments on a Christmas tree dangling in the water column  (Roberts et al. 2009).  A study of a dead colony of Christmas Tree coral found 2500 animals present: these included Brittle Stars, Sea Anenomes, Ampipods and Crinoids (Love et al. 2007). 

Gorgorian corals provide large tree like structures, they support less megafauna than Scleractinian corals because of there smaller surface area and less diversity in microhabitats they provide. They are however a significant habitat for invertebrates Sea stars and Nudibranchs use them to suspension feed and for protection. Their importance as a habitat for fish populations is questionable (Roberts et al. 2009). Faunal diversity can vary between reef habitats, fewer species are associated with live corals than in the frame work of dead coral skeletons (Roberts et al. 2009) 

Figure 16: Antipathes dendrochristos (Image taken from NOAA: URL 4)

The three dimensional structures created by cold-water corals provide numerous surfaces for epifauna to attatch and create an array of micro-habitats:
 1) Smooth coral surface
2) Detritus laden dead surface
3) Cavities made by boring organisms
4) Free space between coral branches
(Roberts et al. 2009) 

A study was conducted in which box core samples from the summit of carbonate mounds were taken from Porcupine Seabight in the North-East Atlantic, the fauna of these mounds was compared to the fauna in off-mound habitats (Henry & Roberts 2007). Results showed that mounds were occupied by more suspension feeders, whereas off mounds were occupied by deposit feeders. This could be because on mounds there is an increased current flow and therefore suspension feeding would be advantageous.  It was concluded that the mounds created a wide range of habitat niches over a small spatial scale (Henry & Roberts 2007)  It is clear the biodiversity can vary greatly across reef habitats.

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