In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals. Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that protect the coral. Most reefs grow best in warm, clear and agitated water. Called "rainforests of the sea", shallow coral reefs form some of Earth's most diverse ecosystems, they occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, worms, echinoderms, sponges and other cnidarians. Coral reefs flourish in ocean waters, they are most found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas. Coral reefs deliver ecosystem services for tourism and shoreline protection.
The annual global economic value of coral reefs is estimated between US$30–375 billion and 9.9 trillion USD. Coral reefs are fragile because they are sensitive to water conditions, they are under threat from excess nutrients, rising temperatures, oceanic acidification, sunscreen use, harmful land-use practices, including runoff and seeps. Most coral reefs were formed after the last glacial period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old; as communities established themselves, the reefs grew pacing rising sea levels. Reefs that rose too could become drowned, without sufficient light. Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and atolls; the majority of these islands are volcanic in origin. Others have tectonic origins. In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle.
He theorized that subsidence of the Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the ocean floor subsides; as the subsidence continues, the fringing reef becomes a barrier reef and an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, can grow to become a barrier reef. Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land.
A barrier reef can encircle an island, once the island sinks below sea level a circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not form complete circles, but are broken in places by storms. Like sea level rise, a subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure; the two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, the history of the change in sea level relative to that substrate. The 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was 120 m lower than in the 21st century; as sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain.
By 13,000 years ago, sea level had risen to 60 m lower than at present, many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands; the corals could overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed in the last 6,000 years; the age of living reef structure is estimated to be between 8,000 years. Although the Great Barrier Reef formed along a continental shelf, not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, it formed 300 -- 1,000 m from shore, stretching for 2,000 km. Healthy tropical coral reefs grow horizontally from 1 to 3 cm per year, grow vertically anywhere from 1 to 25 cm per year; as the name implies, coral reefs are made up of coral skeletons from intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However
Cephalopholis argus known as roi, bluespotted grouper, celestial grouper, is a fish from the Indo-Pacific, variously a commercial gamefish, an invasive species, an aquarium resident. Its species name comes from its resemblance to the "hundred staring eyes" of the monster Argus in Greek mythology; this is a medium-sized fish. Small individuals are dark brown with hundreds of dark-edged iridescent blue spots. Larger specimens sometimes develop four to six lighter vertical bars on the back half of its body; the species is widely distributed, occurring in warm waters from the Red Sea to South Africa and east to French Polynesia and the Pitcairn group. It is present in northern Australia, Lord Howe Island, Japan, has been introduced to the Hawaiian Islands, it makes use of a variety of habitats but prefers the exposed fronts of reefs, at depths of up to 40 m. Hunting, they lie on the surge forward, preferring juvenile surgeonfish and crustaceans. Alternatively they may hover motionless in the water column before attacking.
This grouper may follow and cooperate with another predator species, such as an octopus or eel or camouflage themselves in a school of surgeonfish. Multiple individuals may cooperate to harass an eel to get it to flush prey for them. In the Red Sea, they hunt in the evening; the species sit on a coral head, retreating when startled. Red Sea males defend harems of 2–6 females in territories ranging up to.5 acres. Each female defends part of the territory from the other females; the male visits each female daily. The females emerges from erecting her own dorsal fin and changing to a lighter color, they swim together. Territorial disputes may involve "color fights" in which two males positioning themselves at right angles to each other, they darken their color and switch their bars from dark to light. The loser becomes retreats. If the color fight ends in a draw, the two males may attack each other. In Micronesia, spawning occurs territorially at dusk. During courtship, both sexes darken except for a white keyhole-shaped patch at the center of the body.
Cephalopholis argus is a hardy aquarium fish for those. Its large size combined with its aggressive nature means it is best housed either alone or with other large aggressive fish such as lionfish, moray eels; as a predator it will eat any smaller aquarium inhabitants such as damselfish. Known in Hawaii as roi, the state introduced the species in the 1950s to enhance local fisheries. Hawaii's Division of Aquatic Resources finds; the Roi population there has increased 15 fold since the 1980s. From 1999 to 2005 there was a 23% increase in their population, their biomass is now greater. These predators threaten native reef fish such as goatfish. A University of Hawaii study estimated that in a three-square-mile area off the Kona Coast of Hawaii Island, Roi eat 90 tonnes of reef fish annually— equivalent to 8.2 million fish. Prized as delicious eating in other Pacific regions, in Hawaii's waters roi may contain the ciguatera toxin, which builds up in humans and causes serious illness. A study published in 2007 found that 18% of Roi sampled from Oahu and Hawaii islands had toxins above levels safe for consumption.
Due to high variability of toxin levels between individuals in the same area, toxicity cannot be predicted based on location. There is a weak correlation between the length of Roi and their toxicity, due to high variability, this is not a reliable predictor of toxicity. There is no commercially available testing kit; because of the toxicity issues, Roi does not have a functional fishery, with just an average of $1000 per year in sales. Analysis of stomach contents of Hawaiian roi found that diets consist of 97.7% fish and 2.3% crustaceans. Of the fish eaten, there were 27.1% Scaridae, 18.7% Acanthuridae, 17.6% Squirrelfish, 13.7% Monacanthidae, 9.3% Priacanthidae, 4.3% Chaetodontidae, 2.8% Aulostomidae, 6.9% other consisting of 9 families. Roi are estimated to eat 0.8% of their body weight each day. Roi feed on juvenile fish that have recruited the reef; the family of fish that make up the majority of their diet Scaridae or Parrotfish, are crucial to the coral reef ecosystem by removing algal growth on coral colonies through feeding.
Parrotfish play a large role in the production of sand. Hawaii has the highest rate of endemism of its nearshore marine fish species at 24.3%. The lack of natural predators to control Roi populations along with their high efficiency is a major threat to the unique fish fauna found in Hawaii. Ichtyologist, Dr. Jack Randall, describes the impact of Roi in Hawaii as greater than the impact of fishing and aquarium collection combined. Estimates of consumption on the Kona coast suggest that Roi consume 11% of the total reef fish biomass and 72% of the total number of fish. On Maui, spearfishers participate in "Roi Roundup" tournaments that target these problematic fish, attempting to reduce their numbers and impact; this practice has spread to other islands, where there are similar tournaments that target roi and other invasive fish species. These events not only reduce the roi population, but work to boost public awareness about this issue; the species is classified as Least Concern by the IUCN. and is widespread and common throughout its range.
It is exploited in commercial and recreational fisheri
The ocean sunfish or common mola is one of the heaviest known bony fishes in the world. Adults weigh between 247 and 1,000 kg; the species is native to temperate waters around the globe. It resembles a fish head with a tail, its main body is flattened laterally. Sunfish can be as tall as they are long when their ventral fins are extended. Sunfish are generalist predators that consume small fishes, fish larvae and crustaceans. Sea jellies and salps, once thought to be the primary prey of sunfish, make up only 15% of a sunfish’s diet. Females of the species can produce more eggs than any other known vertebrate, up to 300,000,000 at a time. Sunfish fry resemble miniature pufferfish, with large pectoral fins, a tail fin, body spines uncharacteristic of adult sunfish. Adult sunfish are vulnerable to few natural predators, but sea lions, killer whales, sharks will consume them. Among humans, sunfish are considered a delicacy in some parts of the world, including Japan and Taiwan. In the EU, regulations ban the sale of fishery products derived from the family Molidae.
Sunfish are caught in gillnets. A member of the order Tetraodontiformes, which includes pufferfish and filefish, the sunfish shares many traits common to members of this order; the ocean sunfish, Mola mola, is the type species of the genus. Many of the sunfish's various names allude to its flattened shape, its specific name, mola, is Latin for "millstone", which the fish resembles because of its gray color, rough texture, rounded body. Its common English name, refers to the animal's habit of sunbathing at the surface of the water; the Dutch-, Portuguese-, French-, Catalan-, Spanish-, Italian-, Russian-, Greek- and German-language names maanvis, peixe lua, poisson lune, peix lluna, pez luna, pesce luna, рыба-луна, φεγγαρόψαρο and Mondfisch, mean "moon fish", in reference to its rounded shape. In German, the fish is known as Schwimmender Kopf, or "swimming head". In Polish, it is named meaning "head alone", because it has no true tail. In Swedish and Norwegian it is known as klumpfisk, in Dutch klompvis, in Finnish möhkäkala, all of which meaning "lump fish".
The Chinese translation of its academic name is fān chē yú 翻車魚, meaning "toppled wheel fish". The ocean sunfish has various superseded binomial synonyms, was classified in the pufferfish genus, as Tetraodon mola, it is now placed in its own genus, with three species: Mola mola, Mola tecta and Mola ramsayi. The ocean sunfish, Mola mola, is the type species of the genus; the genus Mola belongs to the family Molidae. This family comprises three genera: Masturus and Ranzania; the common name "sunfish" without qualifier is used to describe the marine family Molidae as well as the freshwater sunfishes in the family Centrarchidae which are unrelated to Molidae. On the other hand, the name "ocean sunfish" and "mola" refer only to the family Molidae; the family Molidae belongs to the order Tetraodontiformes, which includes pufferfish and filefish. It shares many traits common to members of this order, including the four fused teeth that form the characteristic beak and give the order its name. Indeed, sunfish fry resemble spiky pufferfish more.
The caudal fin of the ocean sunfish is replaced by a rounded clavus, creating the body's distinct truncated shape. The body is flattened laterally; the pectoral fins are small and fan-shaped, while the dorsal fin and the anal fin are lengthened making the fish as tall as it is long. Specimens up to 3.2 m in height have been recorded. The mature ocean sunfish has a fin-to-fin length of 2.5 m. The weight of mature specimens can range from 247 to 1,000 kg, but larger individuals are not unheard of; the maximum size is up to 3.3 m in length, 4.2 m across the fins, up to 2,300 kg in mass. The spinal column of M. mola contains fewer vertebrae and is shorter in relation to the body than that of any other fish. Although the sunfish descended from bony ancestors, its skeleton contains cartilaginous tissues, which are lighter than bone, allowing it to grow to sizes impractical for other bony fishes, its teeth are fused into a beak-like structure, it has pharyngeal teeth located in the throat. The sunfish lacks a swim bladder.
Some sources indicate the internal organs contain a concentrated neurotoxin, like the organs of other poisonous tetraodontiformes, while others dispute this claim. In the course of its evolution, the caudal fin of the sunfish disappeared, to be replaced by a lumpy pseudotail, the clavus; this structure is formed by the convergence of the dorsal and anal fins, is used by the fish as a rudder. The smooth-denticled clavus retains 12 fin rays, terminates in a number of rounded ossicles. Ocean sunfish swim near the surface, their protruding dorsal fins are sometimes mistaken for those of sharks. However, the two can be distinguished by the motion of the fin. Sharks, like most fish, swim by moving the tail sideways while keeping the dorsal fin stationary; the sunfish, swings its dorsal fin and anal fin in a characteristic sculling motion. Adult sunfish range from brown with a variety of mottled skin patterns. Coloration is darker on the dorsal surface, fading to a lighter shade ventrally as a form of countershading camouflage.
M. mola exhibits the ability to vary skin coloration from light to dark when under
Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, crayfish, krill and barnacles. The crustacean group is treated as a subphylum, because of recent molecular studies it is now well accepted that the crustacean group is paraphyletic, comprises all animals in the Pancrustacea clade other than hexapods; some crustaceans are more related to insects and other hexapods than they are to certain other crustaceans. The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm, to the Japanese spider crab with a leg span of up to 3.8 m and a mass of 20 kg. Like other arthropods, crustaceans have an exoskeleton, they are distinguished from other groups of arthropods, such as insects and chelicerates, by the possession of biramous limbs, by their larval forms, such as the nauplius stage of branchiopods and copepods. Most crustaceans are free-living aquatic animals, but some are terrestrial, some are parasitic and some are sessile; the group has an extensive fossil record, reaching back to the Cambrian, includes living fossils such as Triops cancriformis, which has existed unchanged since the Triassic period.
More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, the majority of it being shrimp and prawns. Krill and copepods are not as fished, but may be the animals with the greatest biomass on the planet, form a vital part of the food chain; the scientific study of crustaceans is known as carcinology, a scientist who works in carcinology is a carcinologist. The body of a crustacean is composed of segments, which are grouped into three regions: the cephalon or head, the pereon or thorax, the pleon or abdomen; the head and thorax may be fused together to form a cephalothorax, which may be covered by a single large carapace. The crustacean body is protected by the hard exoskeleton, which must be moulted for the animal to grow; the shell around each somite can be divided into a dorsal tergum, ventral sternum and a lateral pleuron. Various parts of the exoskeleton may be fused together; each somite, or body segment can bear a pair of appendages: on the segments of the head, these include two pairs of antennae, the mandibles and maxillae.
The abdomen bears pleopods, ends in a telson, which bears the anus, is flanked by uropods to form a tail fan. The number and variety of appendages in different crustaceans may be responsible for the group's success. Crustacean appendages are biramous, meaning they are divided into two parts, it is unclear whether the biramous condition is a derived state which evolved in crustaceans, or whether the second branch of the limb has been lost in all other groups. Trilobites, for instance possessed biramous appendages; the main body cavity is an open circulatory system, where blood is pumped into the haemocoel by a heart located near the dorsum. Malacostraca have haemocyanin as the oxygen-carrying pigment, while copepods, ostracods and branchiopods have haemoglobins; the alimentary canal consists of a straight tube that has a gizzard-like "gastric mill" for grinding food and a pair of digestive glands that absorb food. Structures that function as kidneys are located near the antennae. A brain exists in the form of ganglia close to the antennae, a collection of major ganglia is found below the gut.
In many decapods, the first pair of pleopods are specialised in the male for sperm transfer. Many terrestrial crustaceans return to the sea to release the eggs. Others, such as woodlice, lay their eggs on land, albeit in damp conditions. In most decapods, the females retain the eggs; the majority of crustaceans are aquatic, living in either marine or freshwater environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs, woodlice. Marine crustaceans are as ubiquitous in the oceans; the majority of crustaceans are motile, moving about independently, although a few taxonomic units are parasitic and live attached to their hosts, adult barnacles live a sessile life – they are attached headfirst to the substrate and cannot move independently. Some branchiurans are able to withstand rapid changes of salinity and will switch hosts from marine to non-marine species. Krill are the bottom layer and the most important part of the food chain in Antarctic animal communities.
Some crustaceans are significant invasive species, such as the Chinese mitten crab, Eriocheir sinensis, the Asian shore crab, Hemigrapsus sanguineus. The majority of crustaceans have separate sexes, reproduce sexually. A small number are hermaphrodites, including barnacles and Cephalocarida; some may change sex during the course of their life. Parthenogenesis is widespread among crustaceans, where viable eggs are produced by a female without needing fertilisation by a male; this occurs in many branchiopods, some os
Triodon macropterus known as the threetooth puffer, is a tetraodontiform fish, the only living species in the genus Triodon and family Triodontidae. Other members of the family are known from fossils stretching back to the Eocene, it is native to the Indo-Pacific. Its name comes from the Ancient Greek τρι- and ὀδούς, refers to the three fused teeth making up a beak-like structure; the threetooth puffer reaches a maximum length of 54 cm. It has a distinctive shape, with a huge belly flap as larger than its body; the flap bears an eye-spot, is inflated by rotating the shaft-like pelvis downwards. This makes the animal appear much larger to predators, less to be eaten; the threetooth puffer is known as the black-spot keeled pufferfish, was first scientifically described by Lesson in 1831