The Banda Sea is one of four seas that surround the Maluku Islands of Indonesia, connected to the Pacific Ocean, but surrounded by hundreds of islands, including Timor, as well as the Halmahera and Ceram Seas. It is about 1000 km (600 mi) east to west, and about 500 km (300 mi) north to south.
The Banda Sea is a marine ecoregion, as defined by the World Wildlife Fund. It is part of the Coral Triangle region, which has the greatest diversity of coral reef species in the broader Indo-Pacific.
The islands surrounding the Banda Sea are part of Wallacea, a biogeographical region that contains the islands lying between Asia and Australia which haven't been joined to either continent. The islands of Wallacea are home to a mix of plant and animal species from both tropical Asia (the Indomalayan realm) and the Australasian realm which includes Australia and New Guinea.
The islands are divided among several terrestrial ecoregions. The northern islands of Sulawesi, Buru, and Seram constitute separate tropical moist forest ecoregions. The islands south of the Banda Sea are among the driest in Indonesia, and are home to tropical dry forests. The Timor and Wetar deciduous forests ecoregion includes Timor and Wetar. The Lesser Sunda Islands from Alor through Flores and Sumbawa to Lombok constitute the Lesser Sundas deciduous forests ecoregion.
The Tanimbar Islands, Kai Islands, and Barat Daya Islands (except for Wetar) in the southeastern Banda Sea form the Banda Sea Islands moist deciduous forests ecoregion. These islands are covered in mostly-intact rain forest, and home to a number of endemic plants and animals including twenty-one bird species, a very high number for this small ecoregion. There are only twenty-two native mammals on these islands, including the rare dusky pademelon (Thylogale brunii) and Indonesian tomb bat (Taphozous achates), and the endangered endemic Kei myotis bat (Myotis stalkeri). The birdlife is threatened by egg collectors and even more by cats and rodents that have been introduced to the islands. Yamdena in the Tanimbar Islands is an example of a large and fairly unspoilt habitat and is a protected area. The base for visiting these islands is by plane or ship from Ambon Island to the north. The Banda and Kai Islands, although remote, are visited by tourists for snorkelling and for their unspoilt beaches. Various cetacean species have been recorded including either or both blue and pygmy blue whales and Omura's whales.