The wildlife and environment of the British Indian Ocean Territory (BIOT) are exceptional. The Territory has the greatest marine biodiversity in the UK and its Overseas Territories, as well as some of the cleanest seas and healthiest reef systems in the world. BIOT is home to the world’s biggest arthropod, the coconut crab, which can reach up to one metre across, with densities on Diego Garcia amongst the highest globally. The outer islands and atolls are colonized by internationally important numbers of seabirds, with many thousands of pairs of sooty terns, brown boobies and red-footed boobies regularly breeding there. Endemic species of coral and reef fish inhabit the c. 4,000 km² of shallow coral reefs, which also support over six times the amount of fish that are found on any other Indian Ocean reef.