Crabs are decapod crustaceans of the infraorder Brachyura, which have a short projecting "tail" entirely hidden under the thorax. They live in all the world's oceans, in fresh water, on land, are covered with a thick exoskeleton and have a single pair of pincers. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, crab lice – are not true crabs. Crabs are covered with a thick exoskeleton, composed of mineralized chitin, armed with a single pair of chelae. Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land in tropical regions. Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres. About 850 species of crab are terrestrial or semi-terrestrial species, they were thought to be a monophyletic group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World. The earliest unambiguous crab fossils date from the Jurassic, although Carboniferous Imocaris, known only from its carapace, may be a primitive crab.
The radiation of crabs in the Cretaceous and afterward may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, crabs' main predators. Crabs show marked sexual dimorphism. Males have larger claws, a tendency, pronounced in the fiddler crabs of the genus Uca. In fiddler crabs, males have one claw, enlarged and, used for communication for attracting a mate. Another conspicuous difference is the form of the pleon; this is. Crabs attract a mate through chemical, acoustic, or vibratory means. Pheromones are used by most aquatic crabs, while terrestrial and semiterrestrial crabs use visual signals, such as fiddler crab males waving their large claws to attract females; the vast number of brachyuran crabs have mate belly-to-belly. For many aquatic species, mating takes place just after the female is still soft. Females can store the sperm for a long time before using it to fertilise their eggs; when fertilisation has taken place, the eggs are released onto the female's abdomen, below the tail flap, secured with a sticky material.
In this location, they are protected during embryonic development. Females carrying eggs are called "berried"; when development is complete, the female releases the newly hatched larvae into the water, where they are part of the plankton. The release is timed with the tides; the free-swimming tiny zoea larvae can take advantage of water currents. They have a spine, which reduces the rate of predation by larger animals; the zoea of most species must find food, but some crabs provide enough yolk in the eggs that the larval stages can continue to live off the yolk. Each species has a particular number of zoeal stages, separated by moults, before they change into a megalopa stage, which resembles an adult crab, except for having the abdomen sticking out behind. After one more moult, the crab is a juvenile, living on the bottom rather than floating in the water; this last moult, from megalopa to juvenile, is critical, it must take place in a habitat, suitable for the juvenile to survive. Most species of terrestrial crabs must migrate down to the ocean to release their larvae.
After living for a short time as larvae in the ocean, the juveniles must do this migration in reverse. In many tropical areas with land crabs, these migrations result in considerable roadkill of migrating crabs. Once crabs have become juveniles, they will still have to keep moulting many more times to become adults, they are covered with a hard shell. The moult cycle is coordinated by hormones; when preparing for moult, the old shell is softened and eroded away, while the rudimentary beginnings of a new shell form under it. At the time of moulting, the crab takes in a lot of water to expand and crack open the old shell at a line of weakness along the back edge of the carapace; the crab must extract all of itself – including its legs, mouthparts and the lining of the front and back of the digestive tract – from the old shell. This is a difficult process that takes many hours, if a crab gets stuck, it will die. After freeing itself from the old shell, the crab is soft and hides until its new shell has hardened.
While the new shell is still soft, the crab can expand it to make room for future growth. Crabs walk sideways, because of the articulation of the legs which makes a sidelong gait more efficient. However, some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles; some crabs, notably the Portunidae and Matutidae, are capable of swimming, the Portunidae so as their last pair of walking legs is flattened into swimming paddles. Crabs are active animals with complex behaviour patterns, they can communicate by waving their pincers. Crabs tend to be aggressive towards one another, males fight to gain access to females. On rocky seashores, where nearly all caves and crevices
Physiology is the scientific study of the functions and mechanisms which work within a living system. As a sub-discipline of biology, the focus of physiology is on how organisms, organ systems, organs and biomolecules carry out the chemical and physical functions that exist in a living system. Central to an understanding of physiological functioning is the investigation of the fundamental biophysical and biochemical phenomena, the coordinated homeostatic control mechanisms, the continuous communication between cells; the physiologic state is the condition occurring from normal body function, while the pathological state is centered on the abnormalities that occur in animal diseases, including humans. According to the type of investigated organisms, the field can be divided into, animal physiology, plant physiology, cellular physiology and microbial physiology; the Nobel Prize in Physiology or Medicine is awarded to those who make significant achievements in this discipline by the Royal Swedish Academy of Sciences.
Human physiology seeks to understand the mechanisms that work to keep the human body alive and functioning, through scientific enquiry into the nature of mechanical and biochemical functions of humans, their organs, the cells of which they are composed. The principal level of focus of physiology is at the level of systems within systems; the endocrine and nervous systems play major roles in the reception and transmission of signals that integrate function in animals. Homeostasis is a major aspect with regard to such interactions within plants as well as animals; the biological basis of the study of physiology, integration refers to the overlap of many functions of the systems of the human body, as well as its accompanied form. It is achieved through communication that occurs in a variety of both electrical and chemical. Changes in physiology can impact the mental functions of individuals. Examples of this would be toxic levels of substances. Change in behavior as a result of these substances is used to assess the health of individuals.
Much of the foundation of knowledge in human physiology was provided by animal experimentation. Due to the frequent connection between form and function and anatomy are intrinsically linked and are studied in tandem as part of a medical curriculum. Plant physiology is a subdiscipline of botany concerned with the functioning of plants. Related fields include plant morphology, plant ecology, cell biology, genetics and molecular biology. Fundamental processes of plant physiology include photosynthesis, plant nutrition, nastic movements, photomorphogenesis, circadian rhythms, seed germination and stomata function and transpiration. Absorption of water by roots, production of food in the leaves, growth of shoots towards light are examples of plant physiology. Although there are differences between animal and microbial cells, the basic physiological functions of cells can be divided into the processes of cell division, cell signaling, cell growth, cell metabolism. Microorganisms can be found everywhere on Earth.
Types of microorganisms include archaea, eukaryotes, protists and micro-plants. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel and other bioactive compounds, they are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body microorganisms make up the human microbiota including the essential gut flora, they are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures. Most microorganisms can reproduce and bacteria are able to exchange genes through conjugation and transduction between divergent species; the study of human physiology as a medical field originates in classical Greece, at the time of Hippocrates. Outside of Western tradition, early forms of physiology or anatomy can be reconstructed as having been present at around the same time in China and elsewhere.
Hippocrates incorporated his belief system called the theory of humours, which consisted of four basic substance: earth, water and fire. Each substance is known for having a corresponding humour: black bile, phlegm and yellow bile, respectively. Hippocrates noted some emotional connections to the four humours, which Claudius Galenus would expand on; the critical thinking of Aristotle and his emphasis on the relationship between structure and function marked the beginning of physiology in Ancient Greece. Like Hippocrates, Aristotle took to the humoral theory of disease, which consisted of four primary qualities in life: hot, cold and dry. Claudius Galenus, known as Galen of Pergamum, was the first to use experiments to probe the functions of the body. Unlike Hippocrates, Galen argued that humoral imbalances can be located in specific organs, including the entire body, his modification of this theory better equipped doctors to make more precise diagnoses. Galen played off of Hippocrates idea that emotions were tied to the humours, added the notion of temperaments: sanguine corresponds with blood.
Galen saw the human body consisting of three connected systems: the brain and nerves, which are responsible for thoughts and sensations.
Johngarthia lagostoma is a species of terrestrial crab that lives on Ascension Island and three other islands in the South Atlantic. It grows to a carapace width of 110 mm on Ascension Island, where it is the largest native land animal, it exists with few intermediates. The yellow morph dominates on Ascension Island, while the purple morph is more frequent on Rocas Atoll; the species differs from other Johngarthia species by the form of the third maxilliped. Johngarthia lagostoma lives in burrows among vegetation, at altitudes of up to 400 m, emerging at night to feed on plant matter and on animals. From January to March there is an annual migration to the sea to release the planktonic larvae; the species was first described by Henri Milne-Edwards in 1837 from material sent to him by the naturalists Jean René Constant Quoy and Joseph Paul Gaimard, collected by the French ship Astrolabe. Johngarthia lagostoma is found on Ascension Island, Trindade Island, Fernando de Noronha and the Rocas Atoll.
On Ascension Island, J. lagostoma is restricted outside the breeding season to the slopes of Green Mountain, where there is sufficient moisture and vegetation, the rest of the island being too arid for the crab to survive. All the land above 400 metres is suitable habitat for the crabs, as is much of the land above 200 m, they are found at lower altitudes, including the well-watered gardens of Georgetown, the sooty tern breeding colony in the south-west of the island. On Trindade Island, J. lagostoma is abundant wherever plants grow, included the highest parts of the island. The geographic distribution of J. lagostoma across a small number of islands in the southern Atlantic Ocean is unusual, difficult to explain by planktonic dispersal. Its nearest relatives are the other species of Johngarthia, two of which inhabit islands in the Pacific Ocean off Central America, one is found on islands in the Gulf of Guinea; some authors have suggested the existence of former islands, now submerged, which could have acted as "stepping stones" for the colonisation of Ascension Island.
Mature specimens of J. lagostoma are 70–110 millimetres wide across the carapace on Ascension Island. In the family Gecarcinidae, species are separated by the form of the first pleopod, used by males during mating, but there is no difference in the gonopod between J. lagostoma and J. planata. Instead, J. lagostoma differs from other species in the genus by the form of the third maxilliped. The third maxilliped is larger, covering the epistome and the antennules in J. lagostoma but not in other species. Within the species, two distinct colour morphs can be seen; the "yellow" morph has a bright yellow or orange exoskeleton, with white patches on the underside of the walking legs and claws. The "purple" morph has a dark purple exoskeleton, but with the same white patches as on the yellow morph. A few intermediate individuals occur, which are predominantly yellow, but with purple patches on the carapace. On Ascension Island, the yellow morph is the more frequent one, while on the Rocas Atoll, the distribution is more equal.
Darker individuals are thought to be better concealed from predators, but more prone to heat stress during long migrations. Before Ascension Island was colonised by Europeans in the 19th century, Johngarthia lagostoma was the only large land animal on the island. Since many species of mammal have been introduced to Ascension Island, now compete with J. lagostoma. J. Lagostoma is active at night and after rain, when it emerges from its burrows, which can be up to 1 metre deep. In 1915, H. A. Baylis reported that it feeds on "decaying vegetation and a certain amount of excreta from sea-birds". In the Wideawake Fairs, J. lagostoma feeds on chicks and eggs of the sooty tern, they have been proposed as a limiting factor in the breeding of petrels on Ascension Island. In May, green sea turtles hatch, J. lagostoma is one of several predators to target the emerging hatchlings, alongside the Ascension frigatebird and feral cats. The crabs find water on and under rocks after condensation has begun to form on their cool surfaces at night.
In the late nineteenth century, a bounty was levied on J. lagostoma in order to reduce its numbers. Hunters were paid 6 pence for every hundred claws collected. In 1879, the total bag for the island comprised 66 cats, 4,013 mice, 7,683 rats and 80,414 land crabs; the current population is much smaller, the low level of recruitment and lack of juveniles suggests that the species may become endangered. Although juvenile and adult J. lagostoma are exclusively terrestrial, the larvae are marine and planktonic. In order to release their offspring, the adults therefore have to migrate to the sea, as seen in other land crabs, such as the Christmas Island red crab, Gecarcoidea natalis. In most members of the family Gecarcinidae, migration coincides with the rainy season, whi
Fresh water is any occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, icebergs, ponds, rivers and underground water called groundwater. Fresh water is characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. Fresh water is not the same as potable water. Much of the earth's fresh water is unsuitable for drinking without some treatment. Fresh water can become polluted by human activities or due to occurring processes, such as erosion. Water is critical to the survival of all living organisms; some organisms can thrive on salt water, but the great majority of higher plants and most mammals need fresh water to live. Fresh water can be defined as water with less than 500 parts per million of dissolved salts. Other sources give higher upper salinity limits for e.g. 1000 ppm or 3000 ppm. Fresh water habitats are classified as either lentic systems, which are the stillwaters including ponds, lakes and mires.
There is, in addition, a zone which bridges between groundwater and lotic systems, the hyporheic zone, which underlies many larger rivers and can contain more water than is seen in the open channel. It may be in direct contact with the underlying underground water; the majority of fresh water on Earth is in ice caps. The source of all fresh water is precipitation from the atmosphere, in the form of mist and snow. Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled. In industrialized areas rain is acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories and aircraft and from the atmospheric emissions of industry. In some cases this acid rain results in pollution of rivers. In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds.
This can give rise to elevated concentrations of sodium, chloride and sulfate as well as many other compounds in smaller concentrations. In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but by the soluble components of those soils. Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa. Saline water in oceans and saline groundwater make up about 97% of all the water on Earth. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers and snow, 0.5–0.75% as fresh groundwater and soil moisture, less than 0.01% of it as surface water in lakes and rivers. Freshwater lakes contain about 87% of this fresh surface water, including 29% in the African Great Lakes, 22% in Lake Baikal in Russia, 21% in the North American Great Lakes, 14% in other lakes.
Swamps have most of the balance with only a small amount in rivers, most notably the Amazon River. The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers. Most of the world's fresh water is frozen in ice sheets. Many areas suffer from lack of distribution such as deserts. Water is a critical issue for the survival of all living organisms; some can use salt water but many organisms including the great majority of higher plants and most mammals must have access to fresh water to live. Some terrestrial mammals desert rodents, appear to survive without drinking, but they do generate water through the metabolism of cereal seeds, they have mechanisms to conserve water to the maximum degree. Fresh water creates a hypotonic environment for aquatic organisms; this is problematic for some organisms with pervious skins or with gill membranes, whose cell membranes may burst if excess water is not excreted.
Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between fresh water and saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; the eel uses the hormone prolactin, while in salmon the hormone cortisol plays a key role during this process. Many sea birds have special glands at the base of the bill; the marine iguanas on the Galápagos Islands excrete excess salt through a nasal gland and they sneeze out a salty excretion. Freshwater molluscs include freshwater snails and freshwater bivalves. Freshwater crustaceans include crayfish. Freshwater biodiversity faces many threats; the World Wide Fund for Nature's Living Planet Index noted an 83% decline in the populations of freshwater vertebrates between 1970 and 2014.
These declines continue to outpace
There are around 1,300 species of freshwater crabs, distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs which release thousands of planktonic larvae; this limits the dispersal abilities of freshwater crabs, so they tend to be endemic to small areas. As a result, a large proportion are threatened with extinction. There are more than 1,300 described species of freshwater crabs, out of a total of 6,700 species of crabs across all environments; the total number of species of freshwater crabs, including undescribed species is thought to be up to 65% higher up to 2,155 species, although most of the additional species are unknown to science. They belong to eight families, each with a limited distribution, although various crabs from other families are able to tolerate freshwater conditions or are secondarily adapted to fresh water; the phylogenetic relationships between these families is still a matter of debate, it is therefore unclear how many times the freshwater lifestyle has evolved among the true crabs.
The eight families are: Superfamily TrichodactyloideaTrichodactylidae Superfamily Potamoidea Potamidae Potamonautidae Deckeniidae – treated as part of Potamonautidae Platythelphusidae – treated as part of PotamonautidaeSuperfamily GecarcinucoideaGecarcinucidae Parathelphusidae Superfamily Pseudothelphusoidea Pseudothelphusidae The fossil record of freshwater organisms is poor, so few fossils of freshwater crabs have been found. The oldest is Tanzanonautes tuerkayi, from the Oligocene of East Africa, the evolution of freshwater crabs is to post-date the break-up of the supercontinent Gondwana. Members of the family Aeglidae and Clibanarius fonticola are restricted to freshwater, but these "crab-like" crustaceans are members of the infraorder Anomura; the external morphology of freshwater crabs varies little, so the form of the gonopod is of critical importance for classification. Development of freshwater crabs is characteristically direct, where the eggs hatch as juveniles, with the larval stages passing within the egg.
The broods comprise only a few hundred eggs each of, quite large, at a diameter of around 1 mm. The colonisation of fresh water has required crabs to alter their water balance. In addition to their gills, freshwater crabs have a "pseudo-lung" in their gill chamber that allows them to breathe in air; these developments have pre-adapted freshwater crabs for terrestrial living, although freshwater crabs need to return to water periodically in order to excrete ammonia. Freshwater crabs are found throughout the sub-tropical regions of the world, they live in a wide range of water bodies, from fast-flowing rivers to swamps, as well as in tree boles or caves. They are nocturnal, emerging to feed at night; some species provide important food sources for various vertebrates. A number of freshwater crabs are secondary hosts of flukes in the genus Paragonimus, which causes paragonimiasis in humans; the majority of species are narrow endemics. This is at least attributable to their poor dispersal abilities and low fecundity, to habitat fragmentation caused by the world's human population.
In West Africa, species that live in savannahs have wider ranges than species from the rainforest. Every species of freshwater crab described so far has been assessed by the International Union for Conservation of Nature. For instance, all but one of Sri Lanka's 50 freshwater crab species are endemic to that country, more than half are critically endangered. Neil Cumberlidge. "Freshwater Crab Biology". Northern Michigan University. Archived from the original on July 20, 2011
The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own. An egg results from fertilization of an egg cell. Most arthropods and mollusks lay eggs, although some, such as scorpions do not. Reptile eggs, bird eggs, monotreme eggs are laid out of water, are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are kept within a warm and favorable temperature range while the embryo grows; when the embryo is adequately developed it hatches, i.e. breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to pip, or break the eggshell or covering; the largest recorded egg is from a whale shark, was 30 cm × 14 cm × 9 cm in size. Whale shark eggs hatch within the mother. At 1.5 kg and up to 17.8 cm × 14 cm, the ostrich egg is the largest egg of any living bird, though the extinct elephant bird and some dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg; some eggs laid by reptiles and most fish, amphibians and other invertebrates can be smaller.
Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells". Several major groups of animals have distinguishable eggs; the most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Large numbers of eggs are laid at one time and the eggs are left to develop without parental care; when the larvae hatch from the egg, they carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die. A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally; however the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother gives birth to mature young.
In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism. In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother providing direct nourishment; the eggs of fish and amphibians are jellylike. Cartilagenous fish eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally with the male inseminating the eggs after the female lays them; these eggs would dry out in the air. Air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina. Bird eggs are incubated for a time that varies according to the species. Average clutch sizes range from one to about 17; some birds lay eggs when not fertilized.
The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, protoporphyrin produces reds and browns as a ground color or as spotting. Non-passerines have white eggs, except in some ground-nesting groups such as the Charadriiformes and nightjars, where camouflage is necessary, some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs if there is no need of cryptic colors; however some have suggested that the protoporphyrin markings on passerine eggs act to reduce brittleness by acting as a solid state lubricant. If there is insufficient calcium available in the local soil, the egg shell may be thin in a circle around the broad end. Protoporphyrin speckling compensates for this, increases inversely to the amount of calcium in the soil. For the same reason eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
The color of individual eggs is genetically influenced, appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex determining W chromosome. It used to be thought that color was applied to the shell before laying, but this research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral. In species such as the common guillemot, which nest in large groups, each female's eggs have different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed. Bird eggshells are diverse. For example: cormorant eggs are rough and chalky tinamou eggs are shiny duck eggs are oily and waterproof cassowary eggs are pittedTiny pores in bird eggshells allow the embryo to breathe; the domestic
Ascension Island is an isolated volcanic island, 7°56' south of the Equator in the South Atlantic Ocean. It is about 1,600 kilometres from 2,250 kilometres from the coast of Brazil, it is governed as part of the British Overseas Territory of Saint Helena and Tristan da Cunha, of which the main island, Saint Helena, is around 1,300 kilometres to the southeast. The territory includes the sparsely-populated Tristan da Cunha archipelago, some 3,730 kilometres to the south, about halfway to the Antarctic Circle; the island is named after the day of Ascension Day. It was an important safe haven and coaling station to mariners and for commercial airliners during the days of international air travel by flying boats. During World War II it was an important naval and air station providing antisubmarine warfare bases in the Battle of the Atlantic. Ascension Island was garrisoned by the British Admiralty from 22 October 1815 to 1922; the island is the location of RAF Ascension Island, a Royal Air Force station, a European Space Agency rocket tracking station, an Anglo-American signals intelligence facility and the BBC World Service Atlantic Relay Station.
The island was used extensively as a staging point by the British military during the Falklands War. Ascension Island hosts one of four ground antennas that assist in the operation of the Global Positioning System navigational system. NASA operates a Meter Class Autonomous Telescope on Ascension Island for tracking orbital debris, hazardous to operating spacecraft and astronauts, at a facility called the John Africano NASA/AFRL Orbital Debris Observatory. In 1501, the Portuguese navigator Afonso de Albuquerque sighted the island on Ascension Day and named it Ilha da Ascensão after this feast day. Dry and barren, the island had little appeal for passing ships except for collecting fresh meat, was not claimed for the Portuguese Crown. Mariners could hunt for the numerous seabirds and the enormous female green turtles that laid their eggs on the sandy beaches; the Portuguese introduced goats as a potential source of meat for future mariners. In February 1701, HMS Roebuck, commanded by William Dampier, sank in the common anchoring spot in Clarence Bay to the northwest of the island.
Sixty men survived for two months. After a few days they found the strong water spring in the high interior of the island, in what is now called Breakneck Valley, it is possible that the island was sometimes used as an open prison for criminal mariners, although there is only one documented case of such an exile, a Dutch ship's officer, Leendert Hasenbosch, set ashore at Clarence Bay as a punishment for sodomy in May 1725. British mariners found the Dutchman's tent and diary in January 1726, his diary was published in translation in London that same year, under the title Sodomy Punish'd. Organised settlement of Ascension Island began in 1815, when the British garrisoned it as a precaution after imprisoning Napoleon I on Saint Helena to the southeast. Colonel Edward Nicolls was among those sent there as punishment for what the Crown perceived as excessive support for Seminole Indians during his posting on the future U. S. Gulf Coast during the War of 1812. On 22 October the Cruizer-class brig-sloops Zenobia and Peruvian claimed the island for King George III.
The Royal Navy designated the island as a stone frigate, HMS Ascension, with the classification of "Sloop of War of the smaller class". The location of the island made it a useful stopping-point for communications; the Royal Navy used the island as a victualling station for ships those of the West Africa Squadron working against the slave trade. A garrison of Royal Marines was based at Ascension from 1823. In 1836 the second Beagle voyage visited Ascension. Charles Darwin described it with nothing growing near the coast. Sparse vegetation inland supported "about six hundred sheep, many goats, a few cows & horses", large numbers of guineafowl imported from the Cape Verde islands, rats and land crabs, he noted the care taken to sustain "houses, gardens & fields placed near the summit of the central mountain", cisterns at roadsides to provide drinking water. The springs were managed, "so that a single drop of water may not be lost: indeed the whole island may be compared to a huge ship kept in first-rate order."
In commenting on this, he noted René Primevère Lesson's remark "that the English nation alone would have thought of making the island of Ascension a productive spot. Four years Hooker, with much encouragement from Darwin, advised the Royal Navy that with the help of Kew Gardens, they should institute a long-term plan of shipping trees to Ascension; the planted trees would capture more rain and improve the soil, allowing the barren island to become a garden. So, from 1850 and continuing year on year, ships came with an assortment of plants from botanical gardens in Argentina and South Africa. By the late 1870s Norfolk pines, eucalyptus and banana trees grew in profusion at the highest point of the is