Clipperton Island (Île de la Passion) is an uninhabited coral atoll in the eastern Pacific Ocean, 1,080 km south-west of Mexico. It is the most isolated and most westerly coral reef in the tropical eastern Pacific (TEP). Clipperton is the only atoll in the TEP and its 3.7 km2 coral reef is the largest in the region (Glynn et al, 1996). The atoll has a unique interior lagoon with no outlet, low topographic relief and is surrounded by well-cemented coral reefs that extend beyond a depth of 40 m and are composed predominantly of corals of the genera Porites, Pavona, and Pocillopora (Glynn et al. 1996). The closed lagoon has a strong vertical salinity gradient, and the waters are almost fresh at the surface and highly eutrophic (UNEP/IUCN 1988). Flora in the lagoon is abundant, with extensive seagrass beds that cover 45% of the lagoon's surface (IFRECOR 1998).The TEP is isolated from the central and western Pacific by the Eastern Pacific Barrier (EPB), the largest marine biogeographic barrier in the world (Ekman 1953). This lends interest from a biogeographical perspective, as it is an area with unusual assemblages of both Indo-Pacific and Panamic flora and faunas (Robertson and Allen 1996). It is possible that Clipperton is an important stepping stone for connection between these bioregions.
Clipperton has the highest concentration of endemic reef fishes per unit area found anywhere in the world (Allen 2008). The island has been identified as an Important Bird Area by BirdLife International with the second-largest brown booby colony and the largest masked booby colony in the world. Other bird species include white terns, sooty terns, brown noddies, black noddies, greater frigates, coots, martins, cuckoos and yellow warblers. Ducks have also been reported in the lagoon. The most dramatic changes occurring in the last decades include explosion in the population of the crab, Jongarthia planata, an almost-complete desertification of the island, and an increase in masked boobies (Jost and Andréfouët 2006). Since 2000, the crab population has decreased as they may have reached maximum carrying capacity (Poupin et al., 2009) the introduction of the rat (Rattus rattus), which allowed vegetation to recover and now occupy ~ 46% of the land today (Jost, 2015). The atoll has been occupied at various times by guano miners, would-be settlers or military personnel, mostly from Mexico, which claimed it until international arbitration awarded it to France in 1931. The atoll was later occupied by the U.S. military during WWII. It now falls under the jurisdiction of the Republic of French Polynesia. Despite its remoteness, Clipperton is frequented by sport fishermen, as well as tuna and shark fishermen from various nations.