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Coconut crab
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Anomura
Superfamily: Paguroidea
Family: Coenobitidae
Genus: Birgus
Species: B. latro
Binomial name
Birgus latro
Linnaeus, 1767
Coconut crabs occur on most coasts in the blue area; red points are primary and yellow points secondary places of settlement
Synonyms

Burgus latro (lapsus)

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 in today's atmosphere.[1] 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 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, unga or kaveu in the Cook Islands, and ayuyu in the Marianas where it is sometimes associated with taotaomo'na because of the traditional belief that ancestral spirits can return in the form of animals such as ayuyu.[2]

Contents

History

Most of the early literature on Birgus is of a popular nature and relies heavily on the accounts of early travelers in the tropical Pacific and Indian Oceans (see list in Gordan 1956).[3] These papers usually discuss the crab's reputed habits of climbing coconut palms, clipping off nuts, returning to the ground to husk and hammer open the nut, or carrying the husked nut back up the palm and dropping it repeatedly on the rocks below until breakage. Many of the early observers admitted that their descriptions were second-hand. Based on such an account by Rumphius (1705), Linnaeus (1767) named the crab latro, or "robber" (of nuts).[4] These habits continued to be described in zoological texts, despite the absence of first-hand accounts in the scientific literature of how the coconut crab husked and opened a coconut.

Several accounts of the natural history of Birgus were provided in the 1930s by Harms (1932, 1938) and Reyne (1939). Harms (1938) included observations on the use of the fifth pereiopod in moistening the lung while drinking, and a lengthy discussion of similarities and differences between crabs on Christmas Island and in the Moluccas. He emphasized the Coenobita-like (i.e., from the family Coenobitidae) characteristics of young Birgus that carry a gastropod shell for an extended period.[5] Reyne (1939) reviewed the literature and described the food habits and distribution of Birgus, stressing his belief that the crab did not open coconuts.[6]

The taxonomic position of Birgus as a hermit crab has been documented through the result of studies of its larvae. Borradaile (1900) briefly described the first zoea.[7] Harms (1932) described the shell carrying habit and growth of the glaucothoe.[8] Orlamunder (1942), using material collected by Harms, described the embryology and first zoea.[9] Reese and Kinzie (1968), in their description of the four to five zoeal stages, found that settling and metamorphosis to glaucothoe (a transitional developmental stage between the larval and juvenile stages) occurred primarily on the 24th to 27th days of larval life.[10] Reese (1968) found that only those glaucothoe which entered shells survived after emigrating to land, and considered the use of small gastropod shells by the glaucothoe an example of the retention of ancestral behavior.[11] Held (1963) found that very small Birgus dig a burrow prior to ecdysis and eat the cast-off exoskeleton.[12]

Physical description

Print of a coconut crab from the Dictionnaire d'Histoire Naturelle of 1849

Reports about the size of Birgus latro vary, but most references give a body length of up to 40 cm (16 in)[13], a weight of up to 4.1 kg (9.0 lb), and a leg span of more than 0.91 m (3.0 ft)[14], with males generally being larger than females. There have been reports in the literature of specimens measuring 6 feet (1.8 m) across the thorax and weighing 30 pounds (14 kg).[15][16] They can live more than 30 years [14].

The body of the coconut crab is, like that of all decapods, divided into a front section (cephalothorax), which has 10 legs, and an abdomen. The front-most pair of legs has large claws used to open coconuts, and these claws (chelae) can lift objects up to 29 kg (64 lb). The next two pairs, as with other hermit crabs, are large, powerful walking legs which allow coconut crabs to climb vertically up trees (often coconut palms). The fourth pair of legs is smaller with tweezer-like chelae at the end, allowing young crabs to grip the inside of a shell or coconut husk to carry for protection; adults use this pair for walking and climbing. The last pair of legs is very small and serves only to clean the breathing organs. These legs are usually held inside the carapace, in the cavity containing the breathing organs. There is some difference in color between the animals found on different islands, ranging from light violet through deep purple to brown.

Although Birgus latro is a derived type of hermit crab, only the juveniles use salvaged snail shells to protect their soft abdomens, and adolescents sometimes use broken coconut shells to protect their abdomens. Unlike other hermit crabs, the adult coconut crabs do not carry shells but instead harden their abdominal terga by depositing chitin and chalk. Not being constrained by the physical confines of living in a shell allows this species to grow much larger than other crabs in the family Coenobitidae.[8] Like most true crabs, B. latro bends its tail underneath its body for protection. The hardened abdomen protects the coconut crab and reduces water loss on land, but has to be moulted at periodic intervals. After moulting, it takes about 30 days for the exoskeleton to harden, during which time the animal's body is soft and vulnerable, and it stays hidden for protection.

Respiration

Except as larvae, coconut crabs cannot swim, and even small specimens will drown in water. They use a special organ called a branchiostegal lung to breathe. This organ can be interpreted as a developmental stage between gills and lungs, and is one of the most significant adaptations of the coconut crab to its habitat.[17] The branchiostegal lung contains a tissue similar to that found in gills, but suited to the absorption of oxygen from air, rather than water. This organ is expanded laterally and is evaginated to increase the surface area; located in the cephalothorax, it is optimally placed to reduce both the blood/gas diffusion distance and the return distance of oxygenated blood to the pericardium.[18] Coconut crabs use their hindmost, smallest pair of legs to clean these breathing organs and to moisten them with water. The organs require water to properly function, and the crab provides this by stroking its wet legs over the spongy tissues nearby. Coconut crabs may also drink water from small puddles by transferring it from their chelipeds to their maxillipeds.[19]

In addition to the branchiostegal lung, the coconut crab has an additional rudimentary set of gills. Although these gills are comparable in number to aquatic species from the families Paguridae and the Diogenidae, they are reduced in size and have comparatively less surface area.[18] While these gills were probably used to breathe under water in the evolutionary history of the species, they no longer provide sufficient oxygen, reflecting a decreased dependence on the gills for gas exchange and the development of other respiratory surfaces.[18]

Sense of smell

Another distinctive organ of the coconut crab is its "nose". The process of smelling works very differently depending on whether the smelled molecules are hydrophilic molecules in water or hydrophobic molecules in air. As most crabs live in the water, they have specialized organs called aesthetascs on their antennae to determine both the concentration and the direction of a smell. However, as coconut crabs live on the land, the aesthetascs on their antennae differ significantly from those of other crabs and look more like the smelling organs of insects, called sensilia. While insects and the coconut crab originate from different evolutionary paths, the same need to detect smells in the air led to the development of remarkably similar organs, making it an example of convergent evolution. Coconut crabs also flick their antennae as insects do to enhance their reception. They have an excellent sense of smell and can detect interesting odors over large distances. The smells of rotting meat, bananas, and coconuts, all potential food sources, catch their attention especially.[20]

Reproduction

Coconut crabs mate frequently and quickly on dry land in the period from May to September, especially between early June and late August.[21] Male crabs have spermatophores and deposit a mass of spermatophores on the abdomen of the female;[22] the abdomen opens at the base of the third pereiopods, and fertilization is thought to occur on the external surface of the abdomen as the eggs pass through the spermatophore mass.[23] The extrusion of eggs occurs on land in crevices or burrows near the shore.[24] Shortly thereafter, the female lays her eggs and glues them to the underside of her abdomen, carrying the fertilized eggs underneath her body for a few months. At the time of hatching, usually October or November, the female coconut crab releases the eggs into the ocean at high tide. The larvae are of the zoea type, as is usual for decapod crustaceans.

The crab larvae float in the pelagic zone of the ocean with other plankton for about a month, during which a large number of them are eaten by predators. Upon reaching the glaucothoe stage of development, they settle to the bottom, find and wear a suitably-sized gastropod shell, and migrate to the shoreline with other terrestrial hermit crabs.[10] At that time, they sometimes visit dry land. As with all hermit crabs, they change their shells as they grow. After these 28 days, they leave the ocean permanently and lose the ability to breathe in water. Young coconut crabs that cannot find a seashell of the right size also often use broken coconut pieces. When they outgrow their shells, they develop a hardened abdomen. After about four to eight years after hatching, the coconut crab matures and can reproduce. This is an unusually long development period for a crustacean.

Diet

Coconut crabs vary in size and coloring.

The diet of coconut crabs consists primarily of fleshy fruits (particularly Ochrosia ackeringae, Arenga listeri , Pandanus elatus, P. christmatensis), nuts (coconuts Cocos nucifera, Aleurites moluccana), and seeds (Annona reticulata).[25] However, as they are omnivorous creatures, they will consume certain other organic materials such as tortoise hatchlings and dead animals.[26][27] They have also been observed to prey upon other sympatric crabs like Gecarcoidea natalis and Discoplax hirtipes, as well as scavenge on the carcasses of dead conspecifics.[25] During a tagging experiment, one coconut crab was observed catching and eating a Polynesian Rat (Rattus exulans).[28] Recent discoveries suggest that the coconut crab may be responsible for the disappearance of Amelia Earhart, consuming her remains and hoarding her bones in its crab burrow.[29] Coconut crabs often try to steal food from each other and will pull their food into their burrows to be safe while eating.


The coconut crab climbs trees to eat coconuts or fruit, to escape the heat or to escape predators. It is a common perception that the coconut crab cuts the coconuts from the tree to eat them on the ground (hence the German name Palmendieb, which literally means "palm thief," and the Dutch Klapperdief). Prehistoric looking, the crab can take a coconut from the ground and cut it to a husk nut, take it with its claw, climb up a tree ten metres high and drop the husk nut, to access the content inside.[30] Coconut crabs cut holes into coconuts with their strong claws and eat the contents; this behavior is unique in the animal kingdom.

Thomas Hale Streets discussed the behavior in 1877—while doubting that the crab would climb trees to get at the nuts.[31] In the 1980s, Holger Rumpf was able to confirm Streets's report, observing and studying how the crabs open coconuts in the wild. The animal has developed a special technique to do so: if the coconut is still covered with husk, it will use its claws to rip off strips, always starting from the side with the three germination pores, the group of three small circles found on the outside of the coconut. Once the pores are visible, the crab will bang its pincers on one of them until they break. Afterwards, it will turn around and use the smaller pincers on its other legs to pull out the white flesh of the coconut. Using their strong claws, larger individuals can even break the hard coconut into smaller pieces for easier consumption.

Habitat and distribution

Coconut crabs at Bora Bora

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.[31] 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.

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.[32]

In the Pacific, its range only gradually became known. Charles Darwin believed it was only found on "a single coral island north of the Society group."[31] The crab is actually far more widespread, though certainly not abundant on each and every Pacific island it inhabits.[31] 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,[31] and on Caroline Island.

Coconut crabs are considered one of the most terrestrial decapods,[33] with most aspects of its life linked to a terrestrial existence. The crab drowns in sea water in less than a day.[34] 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[citation needed] 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.

Relationship with humans

This hermit crab, with its intimidating size and strength, has a special position in the culture of many human societies which share its range. The coconut crab is admired for its strength, and it is said that villagers use this animal to guard their coconut plantations. The coconut crab, especially if it is not yet fully grown, is also sold as a pet, for example, in Tokyo.[35] The cage must be strong enough that the animal cannot use its powerful claws to escape. Should a coconut crab pinch a person, it will not only cause pain, but is unlikely to release its grip. Thomas Hale Streets reports the following trick, used by Micronesians of the Line Islands, to get a coconut crab to loosen its grip:

It may be interesting to know that in such a dilemma a gentle titillation of the under soft parts of the body with any light material will cause the crab to lose its hold.[31]

The coconut crab is eaten by Southeast Asians and Pacific Islanders and is considered a delicacy and an aphrodisiac, with a taste similar to lobster and crab meat. The most prized parts are the eggs inside the female coconut crab and the fat in the abdomen. Coconut crabs can be cooked like other large crustaceans, by boiling or steaming. Different islands also have a variety of recipes, as for example, coconut crab cooked in coconut milk. While the coconut crab itself is not innately poisonous, it may become so depending on its diet, and cases of coconut crab poisoning have occurred. It is believed that the poison comes from plant toxins, which would explain why some animals are poisonous and others not. Reputedly[citation needed], this poison is considered an aphrodisiac, similar to the highly poisonous pufferfish eaten in Japan. However, coconut crabs are not a commercially significant species and are usually not sold.

Status and conservation

Coconut crab populations in several areas have declined or become extinct due to both habitat loss and human predation.[36][37] It is a worldwide protected species according to the IUCN Invertebrate Red Data Book.[38] However, according to the IUCN Red List criteria, there are not enough data at present to decide if the coconut crab is an endangered species, and therefore, it is provisionally listed as DD (data deficient), cautioning that this assessment is in need of update.[32] There have been conservation management strategies effected in some regions, such as minimum legal size limit restrictions in Guam and Vanuatu, and the capture of ovigerous females has been banned in Guam and the Federated States of Micronesia.[39]

The juvenile coconut crab is vulnerable to introduced carnivores, such as rats and pigs, and ants, such as the yellow crazy ant (Anoplolepis gracilipes). Adult coconut crabs have few natural predators, and significant numbers are eaten only by people. The adults have poor eyesight and detect enemies based on ground vibration.

Overall, it seems that large human populations have a negative effect on the coconut crab population, and in some areas, populations are reported to be declining due to over-harvesting. The coconut crab is protected in some areas, such as the British Indian Ocean Territory with minimum sizes for taking and a protected breeding period.

Notes

  1. ^ Piper R. (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Westport, Conn: Greenwood Press. ISBN 0-313-33922-8. 
  2. ^ "A Giant Spider That Can Crack a Coconut? No, It’s a Crab!". http://www.buzzle.com/articles/a-giant-spider-that-can-crack-a-coconut-no-its-a-crab.html. Retrieved 2009-04-15. 
  3. ^ Gordan J. (1956). "A bibliography of hermit crabs, exclusive of Alcock, 1905.". Bulletin of the American Museum of Natural History 108: 253–352. 
  4. ^ Linnaeus C. (1767) (in Latin). Systema naturae per regna tria naturae: secundum classes, ordines, genera, species cum characteribus, differentiis, sinonimis, locis. (edn 12). 
  5. ^ Harms JW. (1938). "Lebensablauf und Stammesgeschicte des Birgus latro L. von der Weinachtsinsel" (in German). Jenaische Zeitschrift für Naturwissenschaft 71: 1–34. 
  6. ^ Reyne A. (1939). "On the food habits of the coconut crab (Birgus latro L.) with notes on its distribution". Archives Néerlandaises de Zoologie 3: 282–320. 
  7. ^ Borradaile LA. (1900). "On the young of the robber crab". in Willey, A (ed.). Zoological results based on material from New Britain, New Guinea, Loyalty Islands and elsewhere, collected during the years 1895, 1896, 1897. Vol. 5. Cambridge (England). pp. 585–90. 
  8. ^ a b Harms JW. (1932). "Birgus latro Linné als Landkrebs und seine Beziehunger zu den Coenobiten" (in German). Zeitschrift für Wissenschaftliche Zoologie 140: 167–290. 
  9. ^ Orlamünder J. (1942). "Zur Entwicklung un Forbuldung des Birgus latro L. mit besonderer Berücksichtigung des X-Organs" (in German). Zeitschrift für Wissenschaftliche Zoologie 155: 280–316. 
  10. ^ a b Reese ES, Kinzie RA. (1968). "The larval development of the coconut or robber crab Birgus latro (L.) in the laboratory (Anomura, Paguridea)". Crustaceana, suppl. 2. Studies on Decapod Larval Development. Leiden, the Netherlands: Brill. pp. 117–44. 
  11. ^ Reese ES., ES (1968). "Shell use: an adaptation for emigration from the sea in the coconut crab". Science 161 (3839): 385–86. doi:10.1126/science.161.3839.385. PMID 17776741. 
  12. ^ Held EE., Edward E. (1963). "Moulting behavior of Birgus latro". Nature 200 (1963): 799–800. doi:10.1038/200799a0. 
  13. ^ Naskrecki, p. 38.
  14. ^ a b "Terrestrial Ecoregions -- Maldives-Lakshadweep-Chagos Archipelago tropical moist forests (IM0125)". http://www.nationalgeographic.com/wildworld/profiles/terrestrial/im/im0125.html. Retrieved 2009-04-15. 
  15. ^ Vogel HH, Kent JR. (1970). "Life history, behavior, and ecology of the coconut crab Birgus latro". Bulletin of the Ecological Society of America 51: 40. 
  16. ^ Vogel HH, Kent JR. (1971). "A curious case: the coconut crab". Fauna 2: 3–11. 
  17. ^ Storch V, Welsch U. (1984). "Electron microscopic observations on the lungs of the coconut crab, Birgus latro (L.) (Crustacea, Decapoda)" (in German). Zoologischer Anzeiger 212: 73–84. 
  18. ^ a b c Farrelly CA, Greenaway P., C.A.; Greenaway, P. (2004). "The morphology and vasculature of the respiratory organs of terrestrial hermit crabs (Coenobita and Birgus): gills, branchiostegal lungs and abdominal lungs". Arthropod Structure and Development 34 (1): 63–87. doi:10.1016/j.asd.2004.11.002. 
  19. ^ Gross WJ., Warren J. (1955). "Aspects of osmotic and ionic regulation in crabs showing the terrestrial habit". American Naturalist 89: 205–22. doi:10.1086/281884. 
  20. ^ Stensmyr MC, Erland S, Hallberg E, Wallén R, Greenaway P, Hansson BS., Marcus C.; Erland, Susanne; Hallberg, Eric; Wallén, Rita; Greenaway, Peter; Hansson, Bill S. (2005). "Insect-like olfactory adaptations in the terrestrial Giant Robber Crab." (PDF). Current Biology 15 (2): 116–21. doi:10.1016/j.cub.2004.12.069. http://www.bees.unsw.edu.au/school/staff/greenaway/Stensmyr%20et%20al%202005%20Current%20Biology.pdf. 
  21. ^ Sato T, Yoseda K., Taku; Yoseda, Kenzo (2008). "Reproductive season and female maturity size of coconut crab Birgus latro on Hatoma Island, southern Japan". Fisheries Science 74 (6): 1277–82. doi:10.1111/j.1444-2906.2008.01652.x. 
  22. ^ Tudge CC., C. C. (1991). "Spermatophore diversity within and among the hermit crab families, Coenobitidae, Diogenidae, and Paguridae (Paguroidae, Anomura, Decapoda)". Biological Bulletin, Marine Biological Laboratory, Woods Hole 181 (2): 238–47. doi:10.2307/1542095. 
  23. ^ Schiller C, Fielder DR, Brown IW, Obed A. (1991). "Reproduction, early life-history and recruitment". The Coconut Crab:Aspects of Birgus latro biology and ecology in Vanuatu. ACIAR Monograph. pp. 13–35. ISBN 1863200541. 
  24. ^ Sato T, Yoseda K. (2008). "Egg extrusion of coconut crab Birgus latro: direct observation of terrestrial egg extrusion" (PDF). JMBA2 – Biodiversity Records (The Marine Biological Association). http://www.mba.ac.uk/jmba/pdf/6370.pdf. 
  25. ^ a b Wilde JE, Linton SM, Greenaway P., Joanne E.; Linton, Stuart M.; Greenaway, Peter (2004). "Dietary assimilation and the digestive strategy of the omnivorous anomuran land crab Birgus latro (Coenobitidae)". Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 174 (4): 299–308. doi:10.1007/s00360-004-0415-7. 
  26. ^ Greenaway P., Peter (2001). "Sodium and water balance in free-ranging robber crabs, Birgus latro (Anomura: Coenobitidae)". Journal of Crustacean Biology 21 (2): 317–27. doi:10.1651/0278-0372(2001)021[0317:SAWBIF2.0.CO;2]. 
  27. ^ Greenaway P. (2003). "Terrestrial adaptations in the Anomura (Crustacea: Decapoda)". Memoirs of Museum of Victoria 60: 13–26. 
  28. ^ Kessler C., Curt (2005). "Observation of a Coconut Crab, Birgus latro (Linnaeus, 1767) predation on a Polynesian rat, Rattus exulans (Peale, 1848)". Crustaceana 78 (6): 761–62. doi:10.1163/156854005774353485. 
  29. ^ Lorenzi, Rossella. "Earhart's Final Resting Place Believed Found" Discovery News, October 23, 2009. Retrieved: October 26, 2009.
  30. ^ Anon (undtd). Coconut Crabs (Birgus latro L.). p. 5. http://www.botany.hawaii.edu/basch/uhnpscesu/pdfs/sam/AnonundatedaAS.pdf. Retrieved 2009-05-23 from University of Hawaii - National Park Service: Pacific Islands Coral Reef Program - Environmental Reports and Publications - American and (western) Samoa at http://www.botany.hawaii.edu/basch/uhnpscesu/picrp/SamIndex/terInvertTer.htm. 
  31. ^ a b c d e f Streets TH., Thomas H. (1877). "Some account of the natural history of the Fanning group of islands" (First page image). American Naturalist 11 (2): 65–72. doi:10.1086/271824. http://links.jstor.org/sici?sici=0003-0147(187702)11%3A2%3C65%3ASAOTNH%3E2.0.CO%3B2-C. Retrieved 2009-04-15. 
  32. ^ a b Eldredge LG. (1996). "IUCN 2008 Red List - Birgus latro". http://www.iucnredlist.org/apps/redlist/details/2811/0/full. Retrieved 2009-04-15. 
  33. ^ Bliss DE. (1968). "Transition from water to land in decapod crustaceans". American Zoologist 8: 355–92. 
  34. ^ Gross WJ., Warren J. (1955). "Aspects of osmotic regulation in crabs showing the terrestrial habit". American Naturalist 89: 205–22. doi:10.1086/281884. 
  35. ^ Fukase T. (2006). "Pets. 122. Robber crab (Birgus latro)" (in Japanese). Journal of Veterinary Medicine 59 (10): 862–63. 
  36. ^ Amesbury SS. (1980). "Biological studies on the coconut crab (Birgus latro) in the Mariana Islands". University of Guam Technical Report 17: 1–39. 
  37. ^ Fletcher WJ (1993). "Coconut crabs". Nearshore marine resources of the South Pacific: Information for fisheries development and management. International Centre for Ocean Development. pp. 643–81. ISBN 982-02-0082-2. 
  38. ^ Wells SM, Pyle RM, Collins NM. (1983). IUCN Invertebrate Red Data Book: A contribution to the Global Environment Monitoring System. Switzerland: Gland. ISBN 978-2880326029. 
  39. ^ Sato T, Yoseda K, Abe O, Shinuno T., Taku; Yoseda, Kenzo; Abe, Osamu; Shibuno, Takuro (2008). "Male maturity, number of sperm, and spermatophore size relationships in the coconut crab Birgus latro on Hatoma Island, southern Japan". Journal of Crustacean Biology 28 (4): 663–68. doi:10.1651/07-2966.1. 

References

  • Altevogt, R. & Davis, T.A. (1975): "Birgus latro: India's monstrous crab. A study and an appeal". Bulletin of the Department of Marine Sciences, University of Cochin.
  • Barnett, L.K.; Emms, C. & Clarke, D. (1999): "The Coconut or robber Crab (Birgus latro) in the Chagos Archipelago and its captive culture at London Zoo". In: Sheppard, C.R.C. & Seaward, M.R.D. (eds): Ecology of the Chagos Archipelago 2: 273–284, Linnean Society Occasional Publications.
  • Combs, C.A.N.; Alford, A.; Boynton, M. & Henry, R.P. (1992): "Behavioural regulation of haemolymph osmolarity through selective drinking in land crabs, Birgus latro and Gecarcoidea lalandii". Biological Bulletin 182(3): 416–423. PDF fulltext
  • Greenaway, P. & Morris, S. (1989): "Adaptations to a terrestrial existence by the robber crab Birgus latro. III. Nitrogenous excretion." Journal of Experimental Biology 143(1): 333–346. PDF fulltext
  • Greenaway, P.; Taylor, H.H. & Morris, S. (1990): "Adaptations to a terrestrial existence by the robber crab Birgus latro. VI. The role of the excretory system in fluid balance." Journal of Experimental Biology 152(1): 505–519. PDF fulltext
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  • Held, E.E. (1963): "Moulting behaviour of Birgus latro". Nature 200(4908): 799–800. doi:10.1038/200799a0
  • Lavery, S.; Moritz, C. & Fielder, D.R. (1996): "Indo-Pacific population structure and evolutionary history of the Coconut Crab Birgus latro". Molecular Ecology 5(4): 557–570. doi:10.1046/j.1365-294X.1996.00125.x
  • Morris, S.; Taylor, H.H. & Greenaway, P (1991): "Adaptations to a terrestrial existence in the robber crab Birgus latro L. VII. The branchial chamber and its role in urine reprocessing." Journal of Experimental Biology 161(1): 315–331. PDF fulltext
  • Naskrecki, Piotr (2005): The Smaller Majority. Belknap Press of Harvard University Press. ISBN 0-674-01915-6
  • Streets, Thomas H. (1877): "Some Account of the Natural History of the Fanning Group of Islands". Am. Nat. 11(2): 65–72. First page image
  • Taylor, H.H.; Greenaway, P. & Morris, S. (1993): "Adaptations to a terrestrial existence in the robber crab Birgus latro L. VIII. Osmotic and ionic regulation on freshwater and saline drinking regimens". Journal of Experimental Biology 179(1): 93–113. PDF fulltext

External links

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Coconut crab
File:Birgus latro
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Anomura
Superfamily: Paguroidea
Family: Coenobitidae
Genus: Birgus
Leach, 1816
Species: B. latro
Binomial name
Birgus latro
Linnaeus, 1767
File:CoconutCrab distribution
Coconut crabs live on most coasts in the blue area; red points are primary and yellow points secondary places of settlement
Synonyms

Cancer latro Linnaeus, 1767 [1]

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 in today's atmosphere.[2] 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 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, unga or kaveu in the Cook Islands, and ayuyu in the Marianas where it is sometimes associated with taotaomo'na because of the traditional belief that ancestral spirits can return in the form of animals such as ayuyu.[3]

Contents

History

Most of the early European literature on Birgus is of a popular nature and relies heavily on the accounts of early European travelers in the tropical Pacific and Indian Oceans (see list in Gordan 1956).[4] These papers usually discuss the crab's reputed habits of climbing coconut palms, clipping off nuts, returning to the ground to husk and hammer open the nut, or carrying the husked nut back up the palm and dropping it repeatedly on the rocks below until breakage. Many of the early observers admitted that their descriptions were second-hand. Based on such an account by Rumphius (1705), Linnaeus (1767) named the crab latro, or "robber" (of nuts).[5] These habits continued to be described in zoological texts, despite the absence of first-hand accounts in the scientific literature of how the coconut crab husked and opened a coconut.

Several accounts of the natural history of Birgus were provided in the 1930s by Harms (1932, 1938) and Reyne (1939). Harms (1938) included observations on the use of the fifth pereiopod in moistening the lung while drinking, and a lengthy discussion of similarities and differences between crabs on Christmas Island and in the Moluccas. He emphasized the Coenobita-like (i.e., from the family Coenobitidae) characteristics of young Birgus that carry a gastropod shell for an extended period.[6] Reyne (1939) reviewed the literature and described the food habits and distribution of Birgus, stressing his belief that the crab did not open coconuts.[7]

The taxonomic position of Birgus as a hermit crab has been documented through the result of studies of its larvae. Borradaile (1900) briefly described the first zoea.[8] Harms (1932) described the shell carrying habit and growth of the glaucothoe.[9] Orlamunder (1942), using material collected by Harms, described the embryology and first zoea.[10] Reese and Kinzie (1968), in their description of the four to five zoeal stages, found that settling and metamorphosis to glaucothoe (a transitional developmental stage between the larval and juvenile stages) occurred primarily on the 24th to 27th days of larval life.[11] Reese (1968) found that only those glaucothoe which entered shells survived after emigrating to land, and considered the use of small gastropod shells by the glaucothoe an example of the retention of ancestral behavior.[12] Held (1963) found that very small Birgus dig a burrow prior to ecdysis and eat the cast-off exoskeleton.[13]

Physical description

[[File:|thumb|left|upright|Print of a coconut crab from the Dictionnaire d'Histoire Naturelle of 1849]] Reports about the size of Birgus latro vary, but most references give a body length of up to 40 cm (16 in)[14], a weight of up to 4.1 kg (9.0 lb), and a leg span of more than 0.91 m (3.0 ft)[15], with males generally being larger than females. There have been reports in the literature of specimens measuring 6 feet (1.8 m) across the thorax and weighing 30 pounds (14 kg).[16][17] They can live more than 30 years [15].

The body of the coconut crab is, like that of all decapods, divided into a front section (cephalothorax), which has 10 legs, and an abdomen. The front-most pair of legs has large claws used to open coconuts, and these claws (chelae) can lift objects up to 29 kilograms (64 lb). The next two pairs, as with other hermit crabs, are large, powerful walking legs which allow coconut crabs to climb vertically up trees (often coconut palms). The fourth pair of legs is smaller with tweezer-like chelae at the end, allowing young crabs to grip the inside of a shell or coconut husk to carry for protection; adults use this pair for walking and climbing. The last pair of legs is very small and serves only to clean the breathing organs. These legs are usually held inside the carapace, in the cavity containing the breathing organs. There is some difference in color between the animals found on different islands, ranging from light violet through deep purple to brown.

Although Birgus latro is a derived type of hermit crab, only the juveniles use salvaged snail shells to protect their soft abdomens, and adolescents sometimes use broken coconut shells to protect their abdomens. Unlike other hermit crabs, the adult coconut crabs do not carry shells but instead harden their abdominal terga by depositing chitin and chalk. Not being constrained by the physical confines of living in a shell allows this species to grow much larger than other crabs in the family Coenobitidae.[9] Like most true crabs, B. latro bends its tail underneath its body for protection. The hardened abdomen protects the coconut crab and reduces water loss on land, but has to be moulted at periodic intervals. After moulting, it takes about 30 days for the exoskeleton to harden, during which time the animal's body is soft and vulnerable, and it stays hidden for protection.

Respiration

Except as larvae, coconut crabs cannot swim, and even small specimens will drown in water. They use a special organ called a branchiostegal lung to breathe. This organ can be interpreted as a developmental stage between gills and lungs, and is one of the most significant adaptations of the coconut crab to its habitat.[18] The branchiostegal lung contains a tissue similar to that found in gills, but suited to the absorption of oxygen from air, rather than water. This organ is expanded laterally and is evaginated to increase the surface area; located in the cephalothorax, it is optimally placed to reduce both the blood/gas diffusion distance and the return distance of oxygenated blood to the pericardium.[19] Coconut crabs use their hindmost, smallest pair of legs to clean these breathing organs and to moisten them with water. The organs require water to properly function, and the crab provides this by stroking its wet legs over the spongy tissues nearby. Coconut crabs may also drink water from small puddles by transferring it from their chelipeds to their maxillipeds.[20]

In addition to the branchiostegal lung, the coconut crab has an additional rudimentary set of gills. Although these gills are comparable in number to aquatic species from the families Paguridae and the Diogenidae, they are reduced in size and have comparatively less surface area.[19] While these gills were probably used to breathe under water in the evolutionary history of the species, they no longer provide sufficient oxygen, reflecting a decreased dependence on the gills for gas exchange and the development of other respiratory surfaces.

Sense of smell

Another distinctive organ of the coconut crab is its "nose". The process of smelling works very differently depending on whether the smelled molecules are hydrophilic molecules in water or hydrophobic molecules in air. As most crabs live in the water, they have specialized organs called aesthetascs on their antennae to determine both the concentration and the direction of a smell. However, as coconut crabs live on the land, the aesthetascs on their antennae differ significantly from those of other crabs and look more like the smelling organs of insects, called sensilia. While insects and the coconut crab originate from different evolutionary paths, the same need to detect smells in the air led to the development of remarkably similar organs, making it an example of convergent evolution. Coconut crabs also flick their antennae as insects do to enhance their reception. They have an excellent sense of smell and can detect interesting odors over large distances. The smells of rotting meat, bananas, and coconuts, all potential food sources, catch their attention especially.[21]

Reproduction

Coconut crabs mate frequently and quickly on dry land in the period from May to September, especially between early June and late August.[22] Male crabs have spermatophores and deposit a mass of spermatophores on the abdomen of the female;[23] the abdomen opens at the base of the third pereiopods, and fertilization is thought to occur on the external surface of the abdomen as the eggs pass through the spermatophore mass.[24] The extrusion of eggs occurs on land in crevices or burrows near the shore.[25] Shortly thereafter, the female lays her eggs and glues them to the underside of her abdomen, carrying the fertilized eggs underneath her body for a few months. At the time of hatching, usually October or November, the female coconut crab releases the eggs into the ocean at high tide. The larvae are of the zoea type, as is usual for decapod crustaceans.

The crab larvae float in the pelagic zone of the ocean with other plankton for about a month, during which a large number of them are eaten by predators. Upon reaching the glaucothoe stage of development, they settle to the bottom, find and wear a suitably-sized gastropod shell, and migrate to the shoreline with other terrestrial hermit crabs.[11] At that time, they sometimes visit dry land. As with all hermit crabs, they change their shells as they grow. After these 28 days, they leave the ocean permanently and lose the ability to breathe in water. Young coconut crabs that cannot find a seashell of the right size also often use broken coconut pieces. When they outgrow their shells, they develop a hardened abdomen. About four to eight years after hatching, the coconut crab matures and can reproduce. This is an unusually long development period for a crustacean.

Diet

File:Robber
Coconut crabs vary in size and coloring.

The diet of coconut crabs consists primarily of fleshy fruits (particularly Ochrosia ackeringae, Arenga listeri, Pandanus elatus, P. christmatensis), nuts (coconuts Cocos nucifera, Aleurites moluccana), and seeds (Annona reticulata).[26] However, as they are omnivorous creatures, they will consume certain other organic materials such as tortoise hatchlings and dead animals.[27][28] They have also been observed to prey upon other sympatric crabs like Gecarcoidea natalis and Discoplax hirtipes, as well as scavenge on the carcasses of dead of their own kind (conspecifics).[26] During a tagging experiment, one coconut crab was observed catching and eating a Polynesian Rat (Rattus exulans).[29] Recent discoveries suggest that the coconut crab may be responsible for the disappearance of Amelia Earhart's remains; consuming them after her death and hoarding her bones in its crab burrow.[30] Coconut crabs often try to steal food from each other and will pull their food into their burrows to be safe while eating.

The coconut crab climbs trees to eat coconuts or fruit, to escape the heat or to escape predators. It is a common perception that the coconut crab cuts the coconuts from the tree to eat them on the ground (hence the German name Palmendieb, which literally means "palm thief", and the Dutch klapperdief). The crab can take a coconut from the ground and cut it to a husk nut, take it with its claw, climb up a tree ten metres high and drop the husk nut, to access the content inside.[31] Coconut crabs cut holes into coconuts with their strong claws and eat the contents; this behavior is unique in the animal kingdom.

Thomas Hale Streets discussed the behavior in 1877—while doubting that the crab would climb trees to get at the nuts.[32] In the 1980s, Holger Rumpf was able to confirm Streets's report, observing and studying how the crabs open coconuts in the wild. The animal has developed a special technique to do so: if the coconut is still covered with husk, it will use its claws to rip off strips, always starting from the side with the three germination pores, the group of three small circles found on the outside of the coconut. Once the pores are visible, the crab will bang its pincers on one of them until they break. Afterwards, it will turn around and use the smaller pincers on its other legs to pull out the white flesh of the coconut. Using their strong claws, larger individuals can even break the hard coconut into smaller pieces for easier consumption.

Habitat and distribution

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.[32] 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.

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.[33]

In the Pacific, its range only gradually became known. Charles Darwin believed it was only found on "a single coral island north of the Society group."[32] The crab is actually far more widespread, though certainly not abundant on each and every Pacific island it inhabits.[32] 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,[32] and on Caroline Island.

Coconut crabs are considered one of the most terrestrial decapods,[34] with most aspects of its life linked to a terrestrial existence. The crab drowns in sea water in less than a day.[20] As they cannot swim as adults, coconut crabs over time must have colonized the islands as larvae, which can swim, or 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.

Relationship with people

The coconut crab, especially if it is not yet fully grown, is also sold as a pet, for example, in Tokyo.[35] The cage must be strong enough that the animal cannot use its powerful claws to escape. Should a coconut crab pinch a person, it will not only cause pain, but is unlikely to release its grip. Thomas Hale Streets reports the following trick, used by Micronesians of the Line Islands, to get a coconut crab to loosen its grip:

It may be interesting to know that in such a dilemma a gentle titillation of the under soft parts of the body with any light material will cause the crab to lose its hold.[32]

The coconut crab is eaten by Southeast Asians and Pacific Islanders and is considered a delicacy and an aphrodisiac, with a taste similar to lobster and crab meat. The most prized parts are the eggs inside the female coconut crab and the fat in the abdomen. Coconut crabs can be cooked like other large crustaceans, by boiling or steaming. Different islands also have a variety of recipes, as for example, coconut crab cooked in coconut milk. While the coconut crab itself is not innately poisonous, it may become so depending on its diet, and cases of coconut crab poisoning have occurred. It is believed that the poison comes from plant toxins, which would explain why some animals are poisonous and others not. However, coconut crabs are not a commercially significant species and are usually not sold.

Status and conservation

Coconut crab populations in several areas have declined or become extinct due to both habitat loss and human predation.[36][37] It is a worldwide protected species according to the IUCN Invertebrate Red Data Book.[38] However, according to the IUCN Red List criteria, there are not enough data at present to decide if the coconut crab is an endangered species, and therefore, it is provisionally listed as DD (data deficient), cautioning that this assessment is in need of update.[33] There have been conservation management strategies effected in some regions, such as minimum legal size limit restrictions in Guam and Vanuatu, and the capture of ovigerous females has been banned in Guam and the Federated States of Micronesia.[39]

The juvenile coconut crab is vulnerable to introduced carnivores, such as rats and pigs, and ants, such as the yellow crazy ant (Anoplolepis gracilipes). Adult coconut crabs have few natural predators, and significant numbers are eaten only by people. The adults have poor eyesight and detect enemies based on ground vibration.

Overall, it seems that large human populations have a negative effect on the coconut crab population, and in some areas, populations are reported to be declining due to over-harvesting. The coconut crab is protected in some areas, such as the British Indian Ocean Territory with minimum sizes for taking and a protected breeding period.

Notes

  1. ^ Patsy McLaughlin (2009). "Birgus latro (Linnaeus, 1767)". In P. McLaughlin. World Paguroidea database. World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=208668. Retrieved March 26, 2010. 
  2. ^ R. Piper (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals. Westport, CT: Greenwood Press. ISBN 0-313-33922-8. 
  3. ^ "A Giant Spider That Can Crack a Coconut? No, It’s a Crab!". http://www.buzzle.com/articles/a-giant-spider-that-can-crack-a-coconut-no-its-a-crab.html. Retrieved April 15, 2009. 
  4. ^ J. Gordan (1956). [Expression error: Unexpected < operator "A bibliography of hermit crabs, exclusive of Alcock, 1905."]. Bulletin of the American Museum of Natural History 108: 253–352. 
  5. ^ Carl Linnaeus (1767) (in Latin). Systema naturae per regna tria naturae: secundum classes, ordines, genera, species cum characteribus, differentiis, sinonimis, locis. (edn 12). 
  6. ^ J. W. Harms (1938). [Expression error: Unexpected < operator "Lebensablauf und Stammesgeschicte des Birgus latro L. von der Weinachtsinsel"] (in German). Jenaische Zeitschrift für Naturwissenschaft 71: 1–34. 
  7. ^ A. Reyne (1939). [Expression error: Unexpected < operator "On the food habits of the coconut crab (Birgus latro L.) with notes on its distribution"]. Archives Néerlandaises de Zoologie 3: 282–320. 
  8. ^ L. A. Borradaile (1900). "On the young of the robber crab". In A. Willey. Zoological results based on material from New Britain, New Guinea, Loyalty Islands and elsewhere, collected during the years 1895, 1896, 1897. Vol. 5. Cambridge (England). pp. 585–590. 
  9. ^ a b J. W. Harms (1932). [Expression error: Unexpected < operator "Birgus latro Linné als Landkrebs und seine Beziehunger zu den Coenobiten"] (in German). Zeitschrift für Wissenschaftliche Zoologie 140: 167–290. 
  10. ^ J. Orlamünder (1942). [Expression error: Unexpected < operator "Zur Entwicklung un Forbuldung des Birgus latro L. mit besonderer Berücksichtigung des X-Organs"] (in German). Zeitschrift für Wissenschaftliche Zoologie 155: 280–316. 
  11. ^ a b E. S. Reese & R. A. Kinzie (1968). [Expression error: Unexpected < operator Crustaceana]. Suppl. 2. pp. 117–44. 
  12. ^ E. S. Reese (1968). [Expression error: Unexpected < operator "Shell use: an adaptation for emigration from the sea in the coconut crab"]. Science 161 (3839): 385–86. doi:10.1126/science.161.3839.385. PMID 17776741. 
  13. ^ Edward E. Held (1963). [Expression error: Unexpected < operator "Moulting behavior of Birgus latro"]. Nature 200 (4709): 799–800. doi:10.1038/200799a0. 
  14. ^ Piotr Naskrecki (2005). The Smaller Majority. Belknap Press of Harvard University Press. pp. 38. ISBN 0-674-01915-6. 
  15. ^ a b World Wildlife Fund (2001). "Maldives-Lakshadweep-Chagos Archipelago tropical moist forests (IM0125)". Terrestrial Ecoregions. National Geographic. http://www.nationalgeographic.com/wildworld/profiles/terrestrial/im/im0125.html. Retrieved April 15, 2009. 
  16. ^ H. H. Vogel & J. R. Kent (1970). [Expression error: Unexpected < operator "Life history, behavior, and ecology of the coconut crab Birgus latro"]. Bulletin of the Ecological Society of America 51: 40. 
  17. ^ H. H. Vogel & J. R. Kent (1971). [Expression error: Unexpected < operator "A curious case: the coconut crab"]. Fauna 2: 3–11. 
  18. ^ V. Storch & U. Welsch (1984). [Expression error: Unexpected < operator "Electron microscopic observations on the lungs of the coconut crab, Birgus latro (L.) (Crustacea, Decapoda)"] (in German). Zoologischer Anzeiger 212: 73–84. 
  19. ^ a b C. A. Farrelly & P. Greenaway (2004). [Expression error: Unexpected < operator "The morphology and vasculature of the respiratory organs of terrestrial hermit crabs (Coenobita and Birgus): gills, branchiostegal lungs and abdominal lungs"]. Arthropod Structure and Development 34 (1): 63–87. doi:10.1016/j.asd.2004.11.002. 
  20. ^ a b Warren J. Gross (1955). [Expression error: Unexpected < operator "Aspects of osmotic and ionic regulation in crabs showing the terrestrial habit"]. American Naturalist 89: 205–222. doi:10.1086/281884. 
  21. ^ Marcus C. Stensmyr, Susanne Erland, Eric Hallberg, Rita Wallén, Peter Greenaway & Bill S. Hansson (2005). "Insect-like olfactory adaptations in the terrestrial Giant Robber Crab" (PDF). Current Biology 15 (2): 116–21. doi:10.1016/j.cub.2004.12.069. PMID 15668166. http://www.bees.unsw.edu.au/school/staff/greenaway/Stensmyr%20et%20al%202005%20Current%20Biology.pdf. 
  22. ^ Taku Sato & Kenzo Yoseda (2008). [Expression error: Unexpected < operator "Reproductive season and female maturity size of coconut crab Birgus latro on Hatoma Island, southern Japan"]. Fisheries Science 74 (6): 1277–82. doi:10.1111/j.1444-2906.2008.01652.x. 
  23. ^ C. C. Tudge (1991). "Spermatophore diversity within and among the hermit crab families, Coenobitidae, Diogenidae, and Paguridae (Paguroidae, Anomura, Decapoda)". Biological Bulletin, Marine Biological Laboratory, Woods Hole (Marine Biological Laboratory) 181 (2): 238–247. doi:10.2307/1542095. http://jstor.org/stable/1542095. 
  24. ^ C. Schiller, D. R. Fielder, I. W. Brown & A. Obed (1991). "Reproduction, early life-history and recruitment". In I. W. Brown & D. R. Fielder. The Coconut Crab: aspects of Birgus latro biology and ecology in Vanuatu. ACIAR Monograph. pp. 13–35. ISBN 1863200541. 
  25. ^ Taku Sato & Kenzo Yoseda (2008). "Egg extrusion of coconut crab Birgus latro: direct observation of terrestrial egg extrusion" (PDF). JMBA2 – Biodiversity Records (Marine Biological Association). http://www.mba.ac.uk/jmba/pdf/6370.pdf. 
  26. ^ a b Joanne E. Wilde, Stuart M. Linton & Peter Greenaway (2004). [Expression error: Unexpected < operator "Dietary assimilation and the digestive strategy of the omnivorous anomuran land crab Birgus latro (Coenobitidae)"]. Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 174 (4): 299–308. doi:10.1007/s00360-004-0415-7. PMID 14760503. 
  27. ^ Peter Greenaway (2001). [Expression error: Unexpected < operator "Sodium and water balance in free-ranging robber crabs, Birgus latro (Anomura: Coenobitidae)"]. Journal of Crustacean Biology 21 (2): 317–327. doi:10.1651/0278-0372(2001)021[0317:SAWBIF]2.0.CO;2. 
  28. ^ Peter Greenaway (2003). [Expression error: Unexpected < operator "Terrestrial adaptations in the Anomura (Crustacea: Decapoda)"]. Memoirs of Museum Victoria 60: 13–26. 
  29. ^ Curt Kessler (2005). [Expression error: Unexpected < operator "Observation of a coconut crab, Birgus latro (Linnaeus, 1767) predation on a Polynesian rat, Rattus exulans (Peale, 1848)"]. Crustaceana 78 (6): 761–62. doi:10.1163/156854005774353485. 
  30. ^ Rossella Lorenzi (October 23, 2009). "Earhart's Final Resting Place Believed Found". Discovery News. http://dsc.discovery.com/news/2009/10/23/amelia-earhart.html. Retrieved October 26, 2009. 
  31. ^ Anon (undated). Coconut Crabs (Birgus latro L.). p. 5. http://www.botany.hawaii.edu/basch/uhnpscesu/pdfs/sam/AnonundatedaAS.pdf. Retrieved 2009-05-23 from University of Hawaii - National Park Service: Pacific Islands Coral Reef Program - Environmental Reports and Publications - American and (western) Samoa. 
  32. ^ a b c d e f Thomas H. Streets (1877). "Some account of the natural history of the Fanning group of islands" (First page image). American Naturalist 11 (2): 65–72. doi:10.1086/271824. http://links.jstor.org/sici?sici=0003-0147(187702)11%3A2%3C65%3ASAOTNH%3E2.0.CO%3B2-C. Retrieved April 15, 2009. 
  33. ^ a b L. G. Eldredge (1996) Birgus latro In: IUCN 2009. IUCN Red List of Threatened Species. Version 2009.2. www.iucnredlist.org Retrieved on March 26, 2010.
  34. ^ D. E. Bliss (1968). [Expression error: Unexpected < operator "Transition from water to land in decapod crustaceans"]. American Zoologist 8: 355–392. 
  35. ^ T. Fukase (2006). [Expression error: Unexpected < operator "Pets. 122. Robber crab (Birgus latro)"] (in Japanese). Journal of Veterinary Medicine 59 (10): 862–863. 
  36. ^ S. S. Amesbury (1980). [Expression error: Unexpected < operator "Biological studies on the coconut crab (Birgus latro) in the Mariana Islands"]. University of Guam Technical Report 17: 1–39. 
  37. ^ W. J. Fletcher (1993). "Coconut crabs". In A. Wright & L. Hill. Nearshore marine resources of the South Pacific: Information for fisheries development and management. International Centre for Ocean Development. pp. 643–81. ISBN 982-02-0082-2. 
  38. ^ Wells SM, Pyle RM, Collins NM. (1983). IUCN Invertebrate Red Data Book: A contribution to the Global Environment Monitoring System. Switzerland: Gland. ISBN 978-2880326029. 
  39. ^ Taku Sato, Kenzo Yoseda, Osamu Abe & Takuro Shinuno, Taku; Yoseda, Kenzo; Abe, Osamu; Shibuno, Takuro (2008). [Expression error: Unexpected < operator "Male maturity, number of sperm, and spermatophore size relationships in the coconut crab Birgus latro on Hatoma Island, southern Japan"]. Journal of Crustacean Biology 28 (4): 663–668. doi:10.1651/07-2966.1. 

References

  • Altevogt, R. & Davis, T.A. (1975): "Birgus latro: India's monstrous crab. A study and an appeal". Bulletin of the Department of Marine Sciences, University of Cochin.
  • Barnett, L.K.; Emms, C. & Clarke, D. (1999): "The Coconut or robber Crab (Birgus latro) in the Chagos Archipelago and its captive culture at London Zoo". In: Sheppard, C.R.C. & Seaward, M.R.D. (eds): Ecology of the Chagos Archipelago 2: 273–284, Linnean Society Occasional Publications.
  • Combs, C.A.N.; Alford, A.; Boynton, M. & Henry, R.P. (1992): "Behavioural regulation of haemolymph osmolarity through selective drinking in land crabs, Birgus latro and Gecarcoidea lalandii". Biological Bulletin 182(3): 416–423. PDF fulltext
  • Greenaway, P. & Morris, S. (1989): "Adaptations to a terrestrial existence by the robber crab Birgus latro. III. Nitrogenous excretion." Journal of Experimental Biology 143(1): 333–346. PDF fulltext
  • Greenaway, P.; Taylor, H.H. & Morris, S. (1990): "Adaptations to a terrestrial existence by the robber crab Birgus latro. VI. The role of the excretory system in fluid balance." Journal of Experimental Biology 152(1): 505–519. PDF fulltext
  • Grubb, P. (1971): "Ecology of terrestrial decapod crustaceans on Aldabra". Phil. Trans. Roy. Soc. Biol. Sci. 260(836): 411–416. HTML abstract and first page image
  • Lavery, S.; Moritz, C. & Fielder, D.R. (1996): "Indo-Pacific population structure and evolutionary history of the Coconut Crab Birgus latro". Molecular Ecology 5(4): 557–570. doi:10.1046/j.1365-294X.1996.00125.x
  • Morris, S.; Taylor, H.H. & Greenaway, P (1991): "Adaptations to a terrestrial existence in the robber crab Birgus latro L. VII. The branchial chamber and its role in urine reprocessing." Journal of Experimental Biology 161(1): 315–331. PDF fulltext
  • Taylor, H.H.; Greenaway, P. & Morris, S. (1993): "Adaptations to a terrestrial existence in the robber crab Birgus latro L. VIII. Osmotic and ionic regulation on freshwater and saline drinking regimens". Journal of Experimental Biology 179(1): 93–113. PDF fulltext

External links

File:Charybdis japonica.jpg Crustaceans portal


Simple English

Coconut crab
Conservation status
Data deficient (IUCN)
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Superorder: Eucarida
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Anomura
Superfamily: Paguroidea
Family: Coenobitidae
Genus: Birgus
Species: B. latro
Binomial name
Birgus latro
Linnaeus, 1767
Synonyms

Burgus latro (lapsus)

The coconut crab, Birgus latro, is a large edible land crab related to the hermit crab, and are found in the tropical Indian and Pacific Oceans. They eat coconuts for a living. They can climb trees too, but they only eat coconuts that have already fallen to the ground. Coconut crab meat has been considered a local delicacy.








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