Pernafasan Ketam
Kelapa
Except as larvae, coconut crabs cannot swim, and they will
drown if left in water for more than an hour.[10] 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.[15] 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;[11] 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.[16] 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 coconut crab provides this by stroking its wet legs over the spongy
tissues nearby. Coconut crabs may drink water from small puddles by
transferring it from their chelipeds to
their maxillipeds.[17]
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.[16]
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 coconut 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 fertilisation 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 fertilised eggs underneath
her body for a few months. At the time of hatching, the female coconut crab
releases the eggs into the ocean.[23] This usually takes place on rocky shores at dusk,
especially when this coincides with high tide.[25] The empty egg cases remain on the female's body after
the larvae have been released, and the female eats the egg cases within a few
days.[25] The larvae float in the pelagic zone of the ocean with other plankton for three to four weeks,[6] during which a large number of them are eaten by
predators. The larvae pass through three to five zoea stages before
moulting into the post-larval glaucothoe stage; this process
takes from 25 to 33 days.[26] 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.[27] At that time, they sometimes visit dry land.
Afterwards, they leave the ocean permanently and lose the ability to breathe in
water. As with all hermit crabs, they change their shells as they grow. Young
coconut crabs that cannot find a seashell of the right size often use broken
coconut pieces. When they outgrow their shells, they develop a hardened
abdomen. The coconut crab reaches sexual maturity around five years after hatching.[23] They reach their maximum size only after 40 to 60
years.[11]
Coconut crabs live in the Indian Ocean and
the central Pacific Ocean, with
a distribution that closely matches that of the coconut palm.[28] The
western limit of the range of B. latro is Zanzibar, off
the coast of Tanzania,[29] while
the tropics of Cancer and Capricorn mark
the northern and southern limits, respectively, with very few population in
the subtropics, such
as the Ryukyu Islands.[6] There
is evidence that the coconut crab once lived on the mainlands of Australia and Madagascar and
on the island of Mauritius, but
it no longer occurs in any of these places.[6] As
they cannot swim as adults, coconut crabs must have colonised the islands as
planktonic larvae.[30]
Christmas Island in
the Indian Ocean has the largest and densest population of coconut crabs in the
world,[18] although
it is outnumbered there by more than 50 times by the Christmas
Island red crab, Gecarcoidea natalis.[31] Other
Indian Ocean populations exist on the Seychelles,
including Aldabra and Cosmoledo,[32] but
the coconut crab is extinct on the central islands.[33] Coconut
crabs occur on several of the Andaman and Nicobar Islands in
the Bay of Bengal. They
occur on most of the islands, and the northern atolls, of the Chagos Archipelago.[34]
In the Pacific, the coconut
crab's range became known gradually. Charles Darwin believed
it was only found on "a single coral island north of the Society group".[35] The
coconut crab is far more widespread, though it is not abundant on every Pacific
island it inhabits.[35]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 coconut crab is especially frequent on Teraina (Washington
Island), with its abundant coconut palm forest.[35] The Gambier Islands marks
the species' eastern limit.[29]
The diet of coconut crabs
consists primarily of fleshy fruits (particularly Ochrosia ackeringae, Arenga listeri, Pandanus elatus, P.
christmatensis); nuts (Aleurites moluccanus),
drupes (Cocos nucifera) and
seeds (Annona reticulata);[36] and
the pith of
fallen trees.[37] However,
as they are omnivores, they
will consume other organic materials such as tortoise hatchlings
and dead animals.[11][38] They
have been observed to prey upon crabs like Gecarcoidea natalis and Discoplax hirtipes, as
well as scavenge on the carcasses of other coconut crabs.[36] During
a tagging experiment, one coconut crab was observed killing and eating a Polynesian Rat (Rattus
exulans).[39] In
2016, a large coconut crab was observed climbing a tree in order to disable and
consume a red-footed booby on
the Chagos Archipelago.[40]
The coconut crab can take a
coconut from the ground and cut it to a husk nut, take it with its claw, climb
up a tree 10 m (33 ft) high and drop the husk nut, to access the
coconut flesh inside.[41] They
often descend from the trees by falling, and can survive a fall of at least 4.5
metres (15 ft) unhurt.[42] Coconut
crabs cut holes into coconuts with their strong claws and eat the contents,
although it can take several days before the coconut is opened.[37]
Thomas Hale Streets discussed
the behaviour in 1877, doubting that the animal would climb trees to get at the
coconuts.[35] In
the 1980s, Holger Rumpf was able to confirm Streets' report, observing and
studying how they open coconuts in the wild.[37] 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 coconut 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.[43]
Coconut crabs are considered one of the most terrestrial-adapted of the
decapods,[44] with most aspects of its life oriented to, and centered
around such an existence; they will actually drown in sea water in less than a
day.[17]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 reduce water loss from
heat. The coconut crabs' burrows contain very fine yet strong fibres of the
coconut husk which the animal uses as bedding.[35] 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 come out during the day, perhaps to gain an advantage in
the search for food. Other times they will emerge if it is moist or raining,
since these conditions allow them to breathe more easily. They live almost
exclusively on land, returning to the sea only to release their eggs; on Christmas Island, for instance, B. latro is
abundant 6 kilometres (3.7 mi) from the sea.[45]
Adult coconut crabs have no
known predators apart
from other coconut crabs and humans. Its large size and the quality of its meat
means that the coconut crab is extensively hunted and is very rare on islands
with a human population.[46] The
coconut crab is eaten by Southeast Asians and Pacific Islanders and
is considered a delicacy and
an aphrodisiac, and
intensive hunting has threatened the species' survival in some areas.[12] 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.[46][47] For
instance, consumption of the sea mango Cerbera manghas by
the coconut crab may make the coconut crab toxic due to the presence of
cardiac cardenolides.[48]
The pincers of the coconut crab
are powerful enough to cause noticeable pain to a human; furthermore, the
coconut crab will often keep its hold for extended periods of time. Thomas Hale
Streets reports a 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 loosen its hold."[35]
In the Cook Islands, the
coconut crab is known as unga or kaveu, and in
the Mariana Islands it
is called ayuyu, and is sometimes associated with taotaomo'na because
of the traditional belief that ancestral spirits can return in the form of
animals such as the coconut crab.[49]
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