Not all coral reefs develop in the same fashion. Their shape and expanse may vary according to wave action, the play of currents and their more or less rigid relationship with seascape. The basic structure is the so-called fringing reef, whose growth runs more or less parallel to the coast. In this form, the reef gives rise to an internal lagoon with a rubbly seabed separated from the open sea by a strip of coral whose summit lies at a very shallow depth and whose seaward wall (sometimes a soft drop-off interrupted by sandy terraces, sometimes a precipitous slope) hosts the highest number of species.
Stony coral colonies assume a great variety of shapes whose surprising diversity contributes essentially to the reef’s air of “articulated disorder.” Over and above the species that belong to it, a colony’s structure is strongly influenced by wave action and the intensity of currents to which it is subjected. More delicately branched forms and those with a leaf shape prefer to grow in deep and protected lagoons; this is true of the large globular colonies that sometimes form authentic micro-atolls several meters in diameter as the central nucleus dies off and the colony expands toward the edges. Colonies with short, robust branches that facilitate the feeding of polyps by slowing the passage of water have the advantage in turbulent waters.
Among the best known fringing reefs are the reefs characteristic of the Red Sea. So-called barrier reefs are an evolution of this structure and are typical of places where the continental shelf (or platform) moves away from land but continues to offer conditions that safeguard the development of madreporic colonies.
The most famous examples of this type of reef-looking like a more or less oblong platform, composed of parallel structures-are found in Australia’s Great Barrier Reef, in Papua New Guinea and in much of the Caribbean.
Coral atolls embody the third model of reef development. Here, the progressive disappearance of a volcanic island leaves intact the fringing reef that surrounded it in remote times, generating an internal lagoon encircled by a more or less regular ring of coral.
The exposed part of the coral reef includes stretches of reef that are periodically uncovered by the tides, sandy beaches proper, mud flats, and the mangrove forests closely connected to them. Such a variety of environments—and the nutrients they provide—cannot fail to host a wide variety of mammals, reptiles, birds and crustaceans. Mammals include wild boars and various monkeys such as the South-East Asian crab-eating macaque on land, and members of the sirenian family such as dugongs and manatees in water. Among reptiles intermittently associated with the reef, monitor lizards, various semi-aquatic snakes and the dangerous marine crocodile, Crocodylus porosus, are worth naming. Numerous tropical birds feed on fish. Among the best known are various species of pelicans, gannets and boobies, and herons. Among earth-bound crustaceans one cannot fail to cite the ghost crabs that inhabit tropical beaches and the gigantic coconut crab, Birgus latro, which has sadly become quite rare throughout the Pacific.
This structural type is generally found in open seas, and especially well-known examples are found in the Maldives and in the Polynesian atolls. The extreme fragility of the reef’s ecosystem is another important phenomenon that emerges from this short description.
Belonging to the elapid family (the same of cobras and kraits), sea snakes are poisonous reptiles that are perfectly adapted to aquatic life. They wield a powerful neurotoxic secretion and have a distinguishing paddleshaped tail. Some, like Laticauda colubrina, return frequently to land, but others live a purely pelagic existence. They feed exclusively on fish and their eggs.
Not all coral reefs develop in the same fashion. Their shape and expanse may vary according to wave action, the play of currents and their more or less rigid relationship with seascape. The basic structure is the so-called fringing reef, whose growth runs more or less parallel to the coast. In this form, the reef gives rise to an internal lagoon with a rubbly seabed separated from the open sea by a strip of coral whose summit lies at a very shallow depth and whose seaward wall (sometimes a soft drop-off interrupted by sandy terraces, sometimes a precipitous slope) hosts the highest number of species. 
The most famous examples of this type of reef-looking like a more or less oblong platform, composed of parallel structures-are found in Australia’s Great Barrier Reef, in Papua New Guinea and in much of the Caribbean. 
This structural type is generally found in open seas, and especially well-known examples are found in the Maldives and in the Polynesian atolls. The extreme fragility of the reef’s ecosystem is another important phenomenon that emerges from this short description. 