The coastal area of Belize is an outstanding natural system consisting of the largest barrier reef in the northern hemisphere, offshore atolls, several hundred sand cays, mangrove forests, coastal lagoons and estuaries. The system's seven sites illustrate the evolutionary history of reef development and are a significant habitat for threatened species.
The reef extends from the border with Mexico to the north, to near the Guatemalan border to the south. The Belize submarine shelf and its barrier reef, represent the world second largest reef system and the largest reef complex in the Atlantic-Caribbean area. Outside the barrier, there are three large atolls: Turneffe Islands, Lighthouse Reef and Glover's Reef.
Between the mainland and the barrier reef is an extensive offshore lagoon which increases in width and depth from north to south. In the north, water depth averages 2-3 m over a flat, featureless bottom 20-25 km wide. South of Belize City, the shelf gradually deepens forming a channel between the mainland and the outer platform, reaching a depth of 65 m in the Gulf of Honduras.
The approximately 450 sand and mangrove cays confined within the barrier and atolls range in size from small, ephemeral sand spits to larger, permanent islands capable of sustaining human settlements.
A total of 178 terrestrial plants and 247 taxa of marine flora has been described from the area. There are over 500 species of fish, 65 scleritian corals, 45 hydroids and 350 molluscs in the area, plus a great diversity of sponges, marine worms and crustaceans. The area harbours a number of species of conservation concern, including West Indian manatee, green turtle, hawksbill turtle, loggerhead turtle and American crocodile. The West Indian manatee population (300-700 individuals) is probably the largest in the world. Several bird species of conservation concern are found in the cayes and atolls. Major seabird and waterbird colonies include those of the red-footed booby (3,000-4,000 individuals) on Half-Moon Caye, brown booby on Man O'War Caye, and common noddy on Glover's Reef. Other noteworthy breeding birds are the brown pelican and the magnificent frigate bird. The Belize coral reef ecosystem is distinctive in the Western Hemisphere on account of its size, its array of reef types and the luxuriance of corals thriving in such pristine conditions. The are several unusual geophysical features including the nearby contiguous shelf edge barrier reef, the complex maze of patch reefs and faros in a relatively deep shelf lagoon, the unusual of reef types in a small area, the presence of atolls, and the large offshore mangrove cays.
Shell middens at Mayan sites along the coast and on the cayes provide evidence that the reefs were used for fishing some 2500 years ago. Between 300 BC and AD 900, the coastal waters were probably used extensively for fishing by the Mayans, and trading posts, ceremonial centres and burial grounds were established on the cayes. With the decline of the Maya civilization, the reef's resources probably went largely unused for a number of centuries, although early Spanish explorers used the cayes to repair their boats and collect fresh water. By the early 17th century, the coastal water of Belize had however become a heaven for pirates and buccaneers, largely from Britain, who looted Spanish and British trading ships and survived on the abundant marine resources available. Subsequently, many of the pirates, as well as Puritan traders from the Mosquito Coast of Nicaragua, settled in the cayes, becoming fishermen and plantation owners. Since then, there have been a number of waves of immigration into the coastal area, including the Garifuna people, immigrants from Mexico, and most recently North Americans and other foreigners who have been lured by the beauty of the reef and its surroundings and have taken up residence in the cayes.