One of France's five overseas departments, Mayotte is the southernmost island of the Comoros Archipelago, located Indian ocean between Madagascar and the African mainland. The island is the centerpiece of a coral-reef structure that was created over hundreds of thousands of years through volcanic episodes, subsidence and sea-level shifts. Made up of three different structures more than 350 kilometers long, the reef encloses a lagoon with a surface area of 1,100 square kilometers that shelters an opulent biodiversity that includes 2,300 known living species.