The Great Barrier Reef is the worlds largest coral reef system, located in the Coral Sea off the coast of Queensland, Australia. It is composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometers (1,400 miles) over an area of approximately 344,400 square kilometers (133,000 square miles). The reef is home to over 9,000 known species, including 400 types of coral, 1,500 species of fish, and 4,000 types of mollusk. It is also the habitat of species such as the dugong and the large green turtle, which are threatened with extinction. The Great Barrier Reef can be seen from outer space and is the worlds biggest single structure made by living organisms. It was selected as a World Heritage Site in 1981 and is one of the Seven Natural Wonders of the World. The reef is a unique ecosystem and an economic powerhouse, contributing more than $6.4 billion each year to the Australian economy and around 64,000 full-time jobs. Visitors to the Great Barrier Reef can enjoy many experiences, including snorkeling, scuba diving, aircraft or helicopter tours, bare boats, glass-bottomed boat viewing, semi-submersibles, and educational trips.