Clipperton Island

• Category: Marine and Oceanic Biomes.
• Geographic Location: Pacific Ocean.
• Summary: Uninhabited Clipperton Island is the only coral atoll in the eastern Pacific Ocean; its enormous seabird colonies are currently threatened by recently introduced black rats and possibly by commercial fishing.

Clipperton Island is an isolated, uninhabited atoll in the middle of the eastern tropical Pacific Ocean, approximately 800 miles (1,300 kilometers) off the west coast of Mexico. It is the only coral atoll in the entire eastern Pacific Ocean and one of the most isolated reefs anywhere in the world. Although French-owned, it has sometimes been claimed by Mexico. It was intermittently inhabited by guano miners from the 1800s until 1917, and was also occupied by the US military briefly during World War II. Since then, there have been only brief visits by fishers, shipwreck survivors, ham and DX-pedition radio operators, and researchers, except for a few longer expeditions, such as the four-month scientific expedition investigating the island's biota and physical aspects in 2005.

The island is a narrow coral ring approximately 2.4 miles (4 kilometers) long and 1.9 miles (3 kilometers) wide, with a large, completely enclosed central lagoon. The lagoon is mostly brackish and often smells of hydrogen sulphide, although a lens of potable water forms on it after heavy rains. The lagoon has few fish, although it supports dense algal mats at times. Most of the island is low coral rubble with an average elevation of seven feet (two meters), except for Clipperton Rock, a 95-foot (29-meter) volcanic outcrop. The island receives as much as 200 inches (500 centimeters) of rain annually during the rainy season (June to November), and because it lies on a hurricane belt, during heavy storms waves sometimes break over the outer perimeter and into the lagoon.

Biodiversity

A total of 115 species of shore fish have been identified at Clipperton, with about equal proportions of eastern and Indo-West Pacific affinities; nine endemic (found exclusively here) species or subspecies have been identified to date. The island itself is largely devoid of vegetation except for a few scattered clumps of introduced coconut palms, interspersed with spiny grass and low thickets of scrub vegetation. A few tiny islets that dot the lagoon are lushly covered with rushes and other weedy plants.

Two species of reptiles inhabit the island: an endemic skink (Emoia cyanura) and an introduced gecko (Gehyra mutilata). In addition, a large, vivid orange land crab (Gecarcinus planatus) is often present in huge swarms. These crabs feed on bird carcasses and excrement as well as on any vegetation that tries to establish on the island; they are the main reason why the island is nearly without plant life.

Visitors to Clipperton have mostly been impressed by the huge numbers of seabirds that blanket the island and fill the air. These species include: white terns (Gygis alba), masked booby (Sula dactylatra), sooty tern (Sterna fuscata), brown booby (Sula leucogaster), brown noddy (Anous stolidus), black noddy (Anous minutus), and, great frigate (Fregata minor). Ducks are also reportedly common in the lagoon, and migratory landbirds make Clipperton a part-time home during winter trips to the Southern Hemisphere.

Despite the island's being isolated and uninhabited, humans have dramatically altered the ecology of Clipperton Island at times. When the last guano miners departed the island in 1917, they left behind introduced palm trees and pigs. At that time, there were innumerable seabirds nesting on the island, countless numbers of land crabs, and almost no vegetation. However, when a scientific expedition next visited the island in 1958, the effects of feral pigs on the local ecology were clearly obvious. The pigs fed mainly on land crabs, ground-nesting birds, and bird eggs, and because the number of herbivorous land crabs was much reduced, the island was now covered with low, weedy vegetation. Only an estimated 500 brown boobies and 150 masked boobies still survived.

The entire pig population (apparently, fifty-eight individuals) was then killed by expedition members, and when the next expedition visited the island ten years later (in 1968), no pigs were sighted, an estimated 11.5 million land crabs infested the island, nearly all the vegetation was gone, the masked boobies had increased to more than 4,000, and the brown boobies to an estimated 25,000. By 2003, it was determined that there were more than 110,000 masked boobies at Clipperton, a figure that probably represented more than half the world population for that species.

Human Impact

In the twenty-first century, new threats impacted the Clipperton avifauna. In 2000, black rats were found on the island for the first time after two fishing boats wrecked on the beach during a storm. In addition to feeding on smaller birds such as terns, rats preyed on land crabs. By 2005, the crab population had been reduced to the point that vegetation was once again spreading across the island and altering the ecosystem. Also, during the 2005 scientific expedition, almost half of the masked booby chicks on the island perished during an apparent food shortage. This occurred at the same time that a fleet of purse seine vessels were illegally fishing tuna around the island, catching entire schools of yellowfin tuna (Thunnus albacares) at one time. This level of overfishing could have important ramifications because for successful feeding, boobies rely on tuna schools to drive prey to the surface, and without those schools, food shortage is inevitable.

Because Clipperton's isolation has not kept it completely immune from human impact, the island will require monitoring and protection if this important coral reef and bird colony is to persist. The effects of climate change due to global warming are now being studied here. In 2012, a research team from Mexico launched a small expedition; these scientists say Clipperton Island provides an interesting example of how a terrestrial ecosystem survives in the middle of the ocean, and is also a thermometer of sorts for how global warming affects the planet. The researchers noted an abundance of plastic waste products on the island’s northeast shore. These likely washed up there from the mainland. They also noted the presence of waste left behind by former visitors to the island. These include American soldiers from World War II and previous scientific research teams.

Bibliography

Charpy, Löic, ed. Clipperton, Environnement et Biodiversité d'un Microcosme Océanique. Muséum National d'Histoire Naturelle, 2009.

“Clipperton Island - The World Factbook.” CIA, 4 Oct. 2024, www.cia.gov/the-world-factbook/countries/clipperton-island/. Accessed 4 Nov. 2024.

Pitman, Robert L., Lisa T. Ballance, and Charly Bost. “Clipperton Island: Pig Sty, Rat Hole and Booby Prize.” Marine Ornithology 33, no. 2 (2005).

"Plastic Surveying and Collection."The Clipperton Project, 11 May 2022, web.archive.org/web/20120502053953/http://www.clippertonproject.com/plastic-surveying-and-collection/. Accessed 1 Aug. 2022.

Rueda, Manuel. “Mexico: Expedition Sails Towards the Remote and Uninhabited Clipperton Island.” March 1, 2012. . Accessed 4 Nov. 2024.

Sachet, Marie-H. “Flora and Vegetation of Clipperton Island.” Proceedings of the California Academy of Sciences 31, no. 10 (1962).

Schipper, Jan. “Clipperton Island Shrub and Grasslands.” One Earth, www.oneearth.org/ecoregions/clipperton-island-shrub-and-grasslands/. Accessed 4 Nov. 2024.

Weimerskirch, Henri. “Foraging Strategy of Masked Boobies from the Largest Colony in the World: Relationship to Environmental Conditions and Fisheries.” Marine Ecology Progress Series, vol. 362, 2008, pp. 291-302. ResearchGate, doi:10.3354/meps07424. Accessed 4 Nov. 2024.