Reef formation

Reefs develop after initial settlement of larvae onto a substrate (rocky pinnacle, mound etc), followed by growth of the larvae and eventual formation of a small colony (Roberts et al., 2009). Pending suitable conditions, other larvae will settle onto the colony and cementation of the reef occurs with the inclusion of trapped sediment (Roberts et al., 2009). Other corals and animals attached onto the surface of the colony and colonies fuse together as they grow, creating a complex reef framework,where the structure is largely made up of dead remains and a thin outer layer of live corals (Roberts et al., 2009). For example, only the outer 10-30 cm is alive in Oculina varicosa colonies (Reed, 2002). Overall growth of the reef is balanced by the loss of structures through bioerosion from borers, versus recruitment and growth (Freidwald et al., 2004; Roberts et al., 2009).  The eroded material forms “rubble”comprised of dead coral, which falls to the base of the reef and promotes larval settlement in new areas (Roberts et al., 2009). Complex reefs can take up to 1,000 years to form and mounds more than 10,000 years (Roberts et al., 2006), as shown in Fig.4.

Fig. 4. Small scale mound formation in the inner circle and long term, large scale formation on the outer circle. Reproduced from Roberts et al., (2006)

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