Reef Development

Cold-water corals are restricted to temperatures around 4-12oC, outside of these temperatures can cause negative physiological effects. Cold-water corals favour shallow water at high latitudes 50-1000 metres and depths up to 4000 metres at low latitudes (Roberts et al. 2006).
Global distribution is skewed by varying levels of research activity in different locations and the bias of deep water mapping technology in developed countries (Roberts et al. 2006). 

Reef Development
Reefs begin to develop when a coral larvae settles on hard substratum, the larvae grows and starts to form isolated grouped colonies. Continued growth leads to inermingling of these coral colonies, thickets of coral form and associated fauna begins to inhabit the area forming a biocoenosis (Roberts et al. 2009).
As new corals grow old polyps die as their calcium carbonate skeleton begins to erode and they become particularly vulnerable to organisms like Clinoid sponges. These eroding skeletons expand the reefs perimeter trapping sediment in its framework and providing a site for new coral larvae to settle. These sediments infill as new coral continues to grow leading to the development of mounds (Roberts et al. 2006).  Reef growth favours specific hydrodynamic conditions and food availability, if at any time environmental conditions change the reef can bio-erode and die (Roberts et al. 2006). A representation of reef mound growth can be seen in the figure 9 extracted from Roberts (2006).
When daughter colonies grow large enough they begin to restrict water flow to the middle of the coral framework causing it to die, this leads to formation of a ‘Wilson Ring’. A ring of living coral grows around dead skeletons as colonies grow outwards from the center of the reef (Rogers 2004). 

In a typical cold-water coral reef the volume of dead coral skeleton structures exceed the volume of living coral structures (Roberts et al. 2009).  Current driven faunal zonation begins to occur as the reef gets more substantial, areas of the reef exposed to strong currents tend to be occupied by a distinct community of organisms (Mullins et al. 1981). 

Figure 9: Growth of Carbonate Mound and Reef Microhabitats (Image from Roberts et al 2006)

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