The Indo-Pacific, sometimes known as the Indo-West Pacific, is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia. It does not include the temperate and polar regions of the Indian and Pacific oceans, and the Tropical Eastern Pacific, along the Pacific coast of the Americas, is also a distinct marine realm.
The term is especially useful in marine biology, ichthyology, and similar fields, since many marine habitats are continuously connected from Madagascar to Japan and Oceania, and a number of species occur over that range, but are not found in the Atlantic Ocean.
The region has an exceptionally high species richness, including 3000 species of fish, compared with around 1200 in the next richest marine region, the Western Atlantic, and around 500 species of reef building corals, compared with about 50 species in the Western Atlantic.
The WWF and Nature Conservancy divide the Indo-Pacific into three realms (or subrealms), and each of these into a number of marine provinces.
The Western Indo-Pacific covers the western and central portion of the Indian Ocean, including Africa's east coast, the Red Sea, Gulf of Aden, Persian Gulf, Arabian Sea, Bay of Bengal, and Andaman Sea, as well as the coastal waters surrounding Madagascar, the Seychelles, Comoros, Mascarene Islands, Maldives, and Chagos Archipelago.