In 2004, the UK applied for, and received, Ramsar site wetlands conservation status for the lagoon and other waters of Diego Garcia.[83]
Diego Garcia is the largest land mass in the Chagos Archipelago (which includes Peros Banhos, the Salomon Islands, the Three Brothers, the Egmont Islands, and the Great Chagos Bank), being an atoll occupying approximately 174 square kilometres (67 sq mi), of which 27.19 square kilometres (10 sq mi) is dry land.[84] The continuous portion of the atoll rim stretches 64 km (40 mi) from one end to the other, enclosing a lagoon 21 km (13 mi) long and up to 11 km (7 mi) wide, with a 6 km (4 mi) pass opening at the north. Three small islands are located in the pass.[85]
The island consists of the largest continuous dryland rim of all atolls in the world. The dryland rim varies in width from a few hundred metres to 2.4 km. Typical of coral atolls, it has a maximum elevation on some dunes on the ocean side of the rim of 9 m (30 ft) above mean low water. The rim nearly encloses a lagoon about 19 km (12 mi) long and up to 8 km (5.0 mi) wide. The atoll forms a nearly complete rim of land around a lagoon, enclosing 90% of its perimeter, with an opening only in the north. The main island is the largest of about 60 islands which form the Chagos Archipelago. Besides the main island, three small islets are at the mouth of the lagoon: West Island (3.4 ha (8.4 acres)), Middle Island (6 ha (15 acres)) and East Island (11.75 ha (29.0 acres)). A fourth, Anniversary Island, 1 km (1,100 yards) southwest of Middle Island, appears as just a sand bar on satellite images. Both Middle Island and Anniversary Isl
The island consists of the largest continuous dryland rim of all atolls in the world. The dryland rim varies in width from a few hundred metres to 2.4 km. Typical of coral atolls, it has a maximum elevation on some dunes on the ocean side of the rim of 9 m (30 ft) above mean low water. The rim nearly encloses a lagoon about 19 km (12 mi) long and up to 8 km (5.0 mi) wide. The atoll forms a nearly complete rim of land around a lagoon, enclosing 90% of its perimeter, with an opening only in the north. The main island is the largest of about 60 islands which form the Chagos Archipelago. Besides the main island, three small islets are at the mouth of the lagoon: West Island (3.4 ha (8.4 acres)), Middle Island (6 ha (15 acres)) and East Island (11.75 ha (29.0 acres)). A fourth, Anniversary Island, 1 km (1,100 yards) southwest of Middle Island, appears as just a sand bar on satellite images. Both Middle Island and Anniversary Island are part of the Spur Reef complex.[85]
The total area of the atoll is about 170 km2 (66 sq mi). The lagoon area is roughly 120 km2 (46 sq mi) with depths ranging down to about 25 m (82 ft). The total land area (excluding peripheral reefs) is around 30 km2 (12 sq mi). The coral reef surrounding the seaward side of the atoll is generally broad, flat, and shallow around 1 m (3.3 ft) below mean sea level in most locations and varying from 100 to 200 m (330 to 660 ft) in width. This fringing seaward reef shelf comprises an area around 35.2 km2 (14 sq mi). At the outer edge of the reef shelf, the bottom slopes very steeply into deep water, at some locations dropping to more than 450 m (1,500 ft) within 1 km (0.62 mi) of the shore.[85]
In the lagoon, numerous coral heads present hazards to navigation. The shallow reef shelf surrounding the island on the ocean side offers no ocean-side anchorage. The channel and anchorage areas in the northern half of the lagoon are dredged, along with the pre-1971 ship turning basin. Significant saltwater wetlands called barachois exist in the southern half of the lagoon. These small lagoons off of the main lagoon are filled with seawater at high tide and dry at low tide. Scientific expeditions in 1996 and 2006 described the lagoon and surrounding waters of Diego Garcia, along with the rest of the Chagos Archipelago, as "exceptionally unpolluted" and "pristine".[86]
Diego Garcia is frequently subject to earthquakes caused by tectonic plate movement along the Carlsberg Ridge located just to the west of the island. One was recorded in 1812; one measuring 7.6 on the Richter Scale hit on 30 November 1983, at 23:46 local time and lasted 72 seconds, resulting in minor damage including wave damage to a 50-m stretch of the southern end of the island, and another on 2 December 2002, an earthquake measuring 4.6 on the Richter scale struck the island at 12:21 am.[87]
In December 2004, a tsunami generated near Indonesia caused minor shoreline erosion on Barton Point (the northeast point of the atoll of Diego Garcia).[88]
Diego Garcia lies within the influence of the South Equatorial current year-round. The surface currents of the Indian Ocean also have a monsoonal regimen associated with the Asian Monsoonal wind regimen. Sea surface temperatures are in the range of 80–84 °F (27–29 °C) year-round.[89]
Fresh water supply
The island is a haven for several types of crustacean; "warrior crabs" (Cardisoma carnifex) overrun the jungle at night. The extremely large 4-kilogram (8.8 lb) coconut crab or robber crab (Birgus latro) is found here in large numbers. Because of the protections provided the species on this atoll, and the isolation of the east rim of the atoll, the species is recorded in greater densities there than anywhere else in its range (339 crabs/ha).[119]
Mammals
No mammal species are native on Diego Garcia, with no record of bats.[120] Other than rats (Rattus rattus), all "wild" mammal species are feral descendants of domesticated species. During the plantation era, Diego Garcia was home to large herds of Sicilian donkeys (Equus asinus), dozens of horses (Equus caballus), hundreds of dogs (Canis familiaris), and house cats (Felis catus). In 1971, the BIOT Commissioner ordered the extermination of feral dogs following the departure of the last plantation workers, and the program continued through 1975, when the last feral dog was observed and shot.[121] Donkeys, which numbered over 400 in 1972, were down to just 20 individuals in 2005.[122] The last horse was observed in 1995,[122] and by 2005, just two cats were thought to have survived an island-wide eradication program.[citation needed]
Native birds
The total bird list for the Chagos Archipelago, including Diego Garcia, consists of 91 species, with large breeding populations of 16 species. Although no birds are endemic, internationally important seabird colonies exist. Diego Garcia's seabird community includes thriving populations of species which are rapidly declining in other parts of the Indian Ocean. Larg
The island is a haven for several types of crustacean; "warrior crabs" (Cardisoma carnifex) overrun the jungle at night. The extremely large 4-kilogram (8.8 lb) coconut crab or robber crab (Birgus latro) is found here in large numbers. Because of the protections provided the species on this atoll, and the isolation of the east rim of the atoll, the species is recorded in greater densities there than anywhere else in its range (339 crabs/ha).[119]
Mammals
No No mammal species are native on Diego Garcia, with no record of bats.[120] Other than rats (Rattus rattus), all "wild" mammal species are feral descendants of domesticated species. During the plantation era, Diego Garcia was home to large herds of Sicilian donkeys (Equus asinus), dozens of horses (Equus caballus), hundreds of dogs (Canis familiaris), and house cats (Felis catus). In 1971, the BIOT Commissioner ordered the extermination of feral dogs following the departure of the last plantation workers, and the program continued through 1975, when the last feral dog was observed and shot.[121] Donkeys, which numbered over 400 in 1972, were down to just 20 individuals in 2005.[122] The last horse was observed in 1995,[122] and by 2005, just two cats were thought to have survived an island-wide eradication program.[citation needed]
Native birds
Diego Garcia provides suitable foraging and nesting habitat for both the hawksbill turtle (Diego Garcia provides suitable foraging and nesting habitat for both the hawksbill turtle (Eretmochelys imbricata) and the green turtle (Chelonia mydas). Juvenile hawksbills are quite common in the lagoon and at Barachois Sylvane (also known as Turtle Cove) in the southern part of the lagoon. Adult hawksbills and greens are common in the surrounding seas and nest regularly on the ocean-side beaches of the atoll. Hawksbills have been observed nesting during June and July, and from November to March. Greens have been observed nesting in every month; the average female lays three clutches per season, each having an average clutch size of 113 eggs. Diurnal nesting is common in both species. An estimated 300–700 hawksbills and 400–800 greens nest in the Chagos.[127]
Endangered species