Gambier Islands (gămˈbĭr) [key], volcanic islands (6 sq mi/15.5 sq km; 2002 pop. 1,097), South Pacific, near the southeast end of the Tuamotu Archipelago. The group is a part of French Polynesia. It comprises a cluster of four inhabited islands known as Mangareva and many uninhabited atolls. The Mangareva cluster is within a barrier reef having a circumference of c.40 mi (60 km). The islands have copra and coffee plantations and pearl fisheries. Many of the uninhabited atolls are privately owned and are worked for copra. Mangareva is the seat of Rikitea, the capital. Discovered in 1797 by the British (who named the group), the Gambier Islands were annexed by France in 1881. Some of the atolls were used for French nuclear tests.