Coral reefs are the largest biological constructions on earth and are visible from outer space. The complexity of reef systems involves interactions between physical, chemical, biological and geological factors over a range of temporal and spatial scales. Coral reefs manage, clearly through a variety of means, to flourish in nutrient-poor environments. However, this ability is also a necessity: in natural oceanographic settings where upwelling brings nutrients into shallow waters, reefs and thus benthic-algal food sources may be replaced by phytoplankton-based food chains. Coral reefs provide excellent indicators of past sea levels as they are strictly shallow water constructions being strongly restricted in their position relative to contemporary sea levels. Reef corals initially capture space by settlement of planulae from the plankton or by the attachments of coral fragments or buds. They then expand in the plane across the substrate and vertically into the overlying water column.