Chagos Archipelago

• Category: Marine and Oceanic Biomes.
• Geographic Location: Indian Ocean.
• Summary: The Chagos Archipelago, located in the middle of the Indian Ocean, is among the world's largest marine reserves. A group of pristine coral atolls, its reefs provide a breeding and repopulation ground for land, shallow-water, and deep-sea species.

The Chagos Archipelago is an area of seven atolls consisting of some 60 islands in the Indian Ocean, located approximately 310 miles (500 kilometers) south of the Maldives. The atolls are composed of several types of coralline rock structures sitting atop volcanoes in a subterranean mountain ridge, and they include the Great Chagos Bank, the world's largest atoll. The land areas of the archipelago are part of a tropical and subtropical moist broadleaf forest biome, consistent with the region's Maldives and Lakshadweep Archipelagos.

In the early 1970s, the United Kingdom (UK) evicted the native Chagossians from several of the archipelago's islands to accommodate the construction of a military base that would jointly serve UK–U.S. military interests. Currently, military personnel inhabit only Diego Garcia, the largest island. The depopulation of the islands decreased the human impact in the area and the surrounding waters, leaving it all relatively pristine so that biodiversity has flourished in a somewhat uninterrupted way. In 2010, the islands and surrounding waters were declared a no-take zone by the UK, making this marine ecosystem among the world's largest nature reserves.

Coral Reefs

There are around 300 species of coral composing the reefs of the Chagos. Coral coverage has changed over the decadeds, from 65 percent in 1979 to around 10 percent in 2019 due to a number of factors. The remaining coverage is consistently dense and healthy throughout the reefs. In a symbiotic relationship, each polyp houses a class of photosynthetic algae, or zooxanthellae, that provides nutrients for the polyp as well as giving the coral its color. Abnormally high sea surface temperatures in 1998 caused widespread coral bleaching, a phenomenon in which the polyp expel these algae, causing color loss. Such bleaching occurred again in 2015, when the area experienced a heat wave. Over the past century, sea temperatures have risen by an average of 0.23 degrees Fahrenheit (0.13 degrees Celsius) per decade. The increase in temperature is mostly due to greenhouse gas emissions from the burning of fossil fuels. A 1-degree Fahrenheit increase is enough to stress corals. According to scientists from the International Coral Reef Society in 2021, with swift action to slow climate change, some reefs in the Chagos may survive to the end of the century.

Because the algae are photosynthetic, they require clear water to maximize sun exposure. Though most of their energy is supplied by the zooxanthellae in the form of glycerol, corals can prey on zooplankton and, if polyps are larger, sometimes even small fish. Notable coral species in the Chagos include the endemic (native only here) shallow-water brain coral and the deep-water staghorn corals. Human activity impacts the health and vitality of the coral, which also are vulnerable to the predatory starfish ”crown of thorns.” Outbreaks of these starfish can kill a reef.

The reefs provide a home for more than 1,000 species of reef-dwelling and pelagic fish. The reef fish that inhabit the shallower areas of the reef close to shore include the endemic Chagos clownfish, wrasse, and grouper, and such pelagic fish as manta rays, sharks, and tuna. Migratory fish, including skipjack and yellowfin tuna, pass through the Chagos for roughly two months every year, and are then subject to catch by commercial fisheries. Illegal fishing, however, also occurs.

Sharks, top predators in the reef's ecosystems, have decreased in number due to poaching and accidental netting by tuna fisheries. The grey reef shark lives in shallow water near the drop-off zone of the reefs and is an important predator in the shallow-water ecosystem. They feed primarily on bony fish and cephalopods living among the reef. Nurse sharks, also hunted by humans, have similar prey, as do octopus, urchin, and rays.

Flora and Fauna

Winds and passing birds seeded the flora native to the islands, and humans introduced foreign plants; these factors have considerably changed the landscape here over the centuries. Notably, humans introduced coconut palms around 1800 to support the coconut oil industry, clearing natural habitats such as Typha (commonly known as bulrush or cattail) swamp and peat habitats. Few other plant species are able to grow in the abandoned coconut groves, but bird species such as noddies, fairy terns, black rats, and coconut crabs have established habitats there.

Native plant life consists of forty-one flowering plants, four ferns, and several species of mosses, liverworts, fungi, and cyanobacteria. There also are forests of Pisonia and Barrington asiatica, the fish poison tree, and other hardwood trees that are favored by such birds as boobies and frigates for nesting. Open, lightly vegetated areas serve as breeding areas for ground-nesting birds, including terns, noddies, and gulls.

In addition to land-nesting birds, there are large numbers of seabirds that breed in areas free of such predators as rats and cats, usually on the islands that were not used for coconut plantations. The red-footed booby is a remarkable case of a species whose population in the Chagos recovered in the 1970s after a 100-year absence. Also present are species of Puffinus, Sternidae, and sooty terns that nest in groups of great density to discourage predators.

The shores of the Chagos islands are home to hawksbill and green turtles, both species on the International Union for Conservation of Nature Red List. Though they were originally exploited for their shells, their populations are recovering because of strict nature reserves that allow them to breed and forage unmolested by humans.

Bibliography

Koldewey, H. J., D. Curnick, S. Harding, L. Harrison, and M. Gollock. “Potential Benefits to Fisheries and Biodiversity of the Chagos Archipelago/British Indian Ocean Territory as a No-Take Marine Reserve.” Marine Pollution Bulletin 60, no. 11 (2010).

Purkis, Sam. "Scientists Raise Alarm over Coral Reef Health." The Conversation, 23 Jul. 2021, www.maritime-executive.com/editorials/scientists-raise-alarm-over-coral-reef-health. Accessed 7 Nov. 2024.

Sheppard, C. R. C., et al. “Reefs and Islands of the Chagos Archipelago, Indian Ocean: Why it is the World's Largest No-Take Marine Protected Area.” Aquatic Conservation: Marine and Freshwater Ecoystems 22, no. 2 (2012).

Speight, Martin R. and Peter A. Henderson. Marine Ecology: Concepts and Applications. Hoboken, NJ: Wiley-Blackwell, 2010.