THE OCEAN DEEP

The coconut crab, Birgus latro, is the largest land-living arthropod in the world, and is probably at the upper limit of how big terrestrial animals with exoskeletons can become. The species inhabits the coastal forest regions of many Indo-Pacific islands, although localized extinction has occurred where the crab is sympatric with man. Generally nocturnal, they remain hidden during the day and emerge only on some nights to forage. Their body is divided into four regions; the cephalic lobe, forepart, trunk, and opisthosoma. It is a highly apomorphic hermit crab and is known for its ability to crack coconuts with its strong pincers in order to eat the contents. It is the only species of the genus Birgus. It is also called the robber crab or palm thief, because some coconut crabs are rumored to steal shiny items such as pots and silverware from houses and tents. Another name is terrestrial hermit crab, due to the use of shells by the young animals; however, there are other terrestrial hermit crabs which do not get rid of the shell even as adults. These typically in the closely related genus Coenobita are the animals usually called "terrestrial hermit crab"; given the close relationship between Coenobita and Birgus, the term would generally refer to any member of the family Coenobitidae.
The coconut crab also has a range of local names, for example, ayuyu on Guam and unga or kaveu in the Cook Islands. On Guam, it is sometimes referred to as a taotaomo'na coconut crab because of the traditional belief that ancestral spirits can return in the form of animals such as the coconut crab.
Coconut crabs live alone in underground burrows and rock crevices, depending on the local terrain. They dig their own burrows in sand or loose soil. During the day, the animal stays hidden to protect itself from predators and reduce water loss from heat. The crabs' burrows contain very fine yet strong fibers of the coconut husk which the animal uses as bedding. While resting in its burrow, the coconut crab closes the entrances with one of its claws to create the moist microclimate within the burrow necessary for its breathing organs. In areas with a large coconut crab population, some may also come out during the day, perhaps to gain an advantage in the search for food. Coconut crabs will also sometimes come out during the day if it is moist or raining, since these conditions allow them to breathe more easily. They live almost exclusively on land, and some have been found up to 6 kilometres (3.7 mi) from the ocean.
Habitat and distribution
Coconut crabs live in areas from the Indian to the central Pacific Ocean. Christmas Island in the Indian Ocean has the largest and best-preserved population in the world. Other Indian Ocean populations exist on the Seychelles, especially Aldabra, the Glorioso Islands, Astove Island, Assumption Island and Cosmoledo, but the coconut crab is extinct on the central islands. They are also known on several of the Andaman and Nicobar Islands in the Bay of Bengal. Large numbers roam freely in the British-owned Chagos Archipelago, also known as the British Indian Ocean Territories (BIOT). They are protected on these islands from being hunted and/or eaten, with fines of up to 1,500 British pounds (roughly $3,000 USD) per crab consumed. On Mauritius and Rodrigues, they are extinct. In the Pacific, its range only became gradually known. Charles Darwin believed it was only found on "a single coral island north of the Society group."[29] The crab is actually far more widespread, though certainly not abundant on each and every Pacific island it inhabits. Large populations exist on the Cook Islands, especially Pukapuka, Suwarrow, Mangaia, Takutea, Mauke, Atiu, and Palmerston Island. These are close to the eastern limit of its range, as are the Line Islands of Kiribati, where the crab is especially frequent on Teraina (Washington Island), with its abundant coconut palm forest, and on Caroline Island.
Coconut crabs are considered one of the most terrestrial decapods, with most aspects of its life linked to a terrestrial existence. The crab drowns in sea water in less than a day. As they cannot swim as adults, coconut crabs over time must have colonized the islands as larvae, which can swim. However, due to the large distances between the islands, some researchers believe a larva stadium of 28 days is not enough to travel the distance, and they assume juvenile coconut crabs reached other islands on driftwood and other flotsam.
The distribution shows some gaps, as for example around Borneo, Indonesia or New Guinea. These islands were within easy reach of the crab and also have a suitable habitat, yet have no coconut crab population. This is due to the coconut crabs being eaten to extinction by people. However, coconut crabs are known to live on the islands of the Wakatobi Marine National Park in Sulawesi, Indonesia.