Corals are marine invertebrates in the class
Anthozoa of phylum
Cnidaria. They typically live in compact colonies of many identical
individual polyps. The group includes the important reef builders that
inhabit tropical oceans and secrete calcium carbonate to form a hard
A coral "group" is a colony of myriad genetically identical polyps.
Each polyp is a sac-like animal typically only a few millimeters in
diameter and a few centimeters in length. A set of tentacles surround
a central mouth opening. An exoskeleton is excreted near the base.
Over many generations, the colony thus creates a large skeleton
characteristic of the species. Individual heads grow by asexual
reproduction of polyps. Corals also breed sexually by spawning: polyps
of the same species release gametes simultaneously over a period of
one to several nights around a full moon.
Although some corals are able to catch small fish and plankton using
stinging cells on their tentacles, most corals obtain the majority of
their energy and nutrients from photosynthetic unicellular
dinoflagellates in the genus
Symbiodinium that live within their
tissues. These are commonly known as zooxanthellae. Such corals
require sunlight and grow in clear, shallow water, typically at depths
less than 60 metres (200 ft). Corals are major contributors to
the physical structure of the coral reefs that develop in tropical and
subtropical waters, such as the enormous
Great Barrier Reef
Great Barrier Reef off the
coast of Queensland, Australia.
Other corals do not rely on zooxanthellae and can live in much deeper
water, with the cold-water genus
Lophelia surviving as deep as 3,300
metres (10,800 ft). Some have been found on the Darwin Mounds,
north-west of Cape Wrath, Scotland, and others as far north as off the
coast of Washington State and the Aleutian Islands.
2.1 Soft Corals
2.2 Stony Corals
3.2 Intracellular symbionts
4.3 Colony division
6 Evolutionary history
8 Relation to humans
8.4 Climate research
188.8.131.52 Strontium/calcium ratio anomaly
184.108.40.206 Oxygen isotope anomaly
Sea surface temperature
Sea surface temperature and sea surface salinity
220.127.116.11 Limited climate research on current species
12 External links
Phylogeny of Anthozoa, relationships of the orders still undefined
Theophrastus described the red coral, korallion in
his book on stones, implying it was a mineral; but he described it as
a deep-sea plant in his Enquiries on Plants, where he also mentions
large stony plants that reveal bright flowers when under water in the
Gulf of Heroes.
Pliny the Elder
Pliny the Elder stated boldly that several sea
creatures including sea nettles and sponges "are neither animals nor
plants, but are possessed of a third nature (tertius natura)".
Petrus Gyllius copied Pliny, introducing the term zoophyta for this
third group in his 1535 book On the French and Latin Names of the
Fishes of the Marseilles Region; it is popularly but wrongly supposed
Aristotle created the term. Gyllius further noted, following
Aristotle, how hard it was to define what was a plant and what was an
The Persian polymath
Al-Biruni (d. 1048) classified sponges and corals
as animals, arguing that they respond to touch. Nevertheless,
people believed corals to be plants until the eighteenth century, when
William Herschel used a microscope to establish that coral had the
characteristic thin cell membranes of an animal.
The phylogeny of Anthozoans is not clearly understood and a number of
different models have been proposed. Within the Hexacorallia, the sea
anemones, coral anemones and stony corals may constitute a
monophyletic grouping united by their six-fold symmetry and cnidocyte
Octocorallia appears to be monophyletic, and primitive
members of this group may have been stolonate. The cladogram
presented here comes from a 2014 study by Stampar et al. which was
based on the divergence of mitochondrial DNA within the group and on
Corals are classified in the class
Anthozoa of the phylum Cnidaria.
They are divided into three subclasses, Hexacorallia,
Octocorallia, and Ceriantharia. The
the stony corals, the sea anemones and the zoanthids. These groups
have polyps that generally have 6-fold symmetry. The Octocorallia
include blue coral, soft corals, sea pens, and gorgonians (sea fans
and sea whips). These groups have polyps with 8-fold symmetry, each
polyp having eight tentacles and eight mesenteries.
the tube-dwelling anemones.
Fire corals are not true corals, being in the order Anthomedusa
(sometimes known as Anthoathecata) of the class Hydrozoa.
Anatomy of a stony coral polyp
Corals are sessile animals in the class
Anthozoa and differ from most
other cnidarians in not having a medusa stage in their life cycle. The
body unit of the animal is a polyp. Most corals are colonial, the
initial polyp budding to produce another and the colony gradually
developing from this small start. In stony corals, also known as hard
corals, the polyps produce a skeleton composed of calcium carbonate to
strengthen and protect the organism. This is deposited by the polyps
and by the coenosarc, the living tissue that connects them. The polyps
sit in cup-shaped depressions in the skeleton known as corallites.
Colonies of stony coral are very variable in appearance; a single
species may adopt an encrusting, plate-like, bushy, columnar or
massive solid structure, the various forms often being linked to
different types of habitat, with variations in light level and water
movement being significant.
In soft corals, there is no stony skeleton but the tissues are often
toughened by the presence of tiny skeletal elements known as
sclerites, which are made from calcium carbonate. Soft corals are very
variable in form and most are colonial. A few soft corals are
stolonate, but the polyps of most are connected by sheets of
coenosarc. In some species this is thick and the polyps are deeply
embedded. Some soft corals are encrusting or form lobes. Others are
tree-like or whip-like and have a central axial skeleton embedded in
the tissue matrix. This is composed either of a fibrous protein
called gorgonin or of a calcified material. In both stony and soft
corals, the polyps can be retracted, with stony corals relying on
their hard skeleton and cnidocytes for defence against predators, and
soft corals generally relying on chemical defences in the form of
toxic substances present in the tissues known as terpenoids.
Montastraea cavernosa polyps with tentacles extended
The polyps of stony corals have six-fold symmetry while those of soft
corals have eight. The mouth of each polyp is surrounded by a ring of
tentacles. In stony corals these are cylindrical and taper to a point,
but in soft corals they are pinnate with side branches known as
pinnules. In some tropical species these are reduced to mere stubs and
in some they are fused to give a paddle-like appearance. In most
corals, the tentacles are retracted by day and spread out at night to
catch plankton and other small organisms. Shallow water species of
both stony and soft corals can be zooxanthellate, the corals
supplementing their plankton diet with the products of photosynthesis
produced by these symbionts. The polyps interconnect by a complex
and well-developed system of gastrovascular canals, allowing
significant sharing of nutrients and symbionts.
Polyps feed on a variety of small organisms, from microscopic
zooplankton to small fish. The polyp's tentacles immobilize or kill
prey using their nematocysts. These cells carry venom which they
rapidly release in response to contact with another organism. A
dormant nematocyst discharges in response to nearby prey touching the
trigger (cnidocil). A flap (operculum) opens and its stinging
apparatus fires the barb into the prey. The venom is injected through
the hollow filament to immobilise the prey; the tentacles then
manoeuvre the prey to the mouth.
The tentacles then contract to bring the prey into the stomach. Once
the prey is digested, the stomach reopens, allowing the elimination of
waste products and the beginning of the next hunting cycle. They can
scavenge drifting organic molecules and dissolved organic
Many corals, as well as other cnidarian groups such as
Aiptasia (a sea
anemone) form a symbiotic relationship with a class of dinoflagellate
algae, zooxanthellae of the genus Symbiodinium.:24 Aiptasia, a
familiar pest among coral reef aquarium hobbyists, serves as a
valuable model organism in the study of cnidarian-algal symbiosis.
Typically, each polyp harbors one species of algae, and coral species
show a preference for Symbiodinium. Young corals are not born with
zooxanthellae, but acquire the algae from the surrounding environment,
including the water column and local sediment. Via photosynthesis,
these provide energy for the coral, and aid in calcification. The
main benefit of the zooxanthellae is their ability to photosynthesize.
By using this technique, zooxanthellae are able to supply corals with
the products of photosynthesis, including glucose, glycerol, and amino
acids, which the corals can use for energy. As much as 30% of the
tissue of a polyp may be algal material.:23
benefit corals by aiding in waste removal.
The algae benefit from a safe place to live and consume the polyp's
carbon dioxide and nitrogenous waste. Due to the strain the algae can
put on the polyp, stress on the coral often drives them to eject the
algae. Mass ejections are known as coral bleaching, because the algae
contribute to coral's brown coloration; other colors, however, are due
to host coral pigments, such as green fluorescent proteins (GFPs).
Ejection increases the polyp's chance of surviving short-term
stress—they can regain algae, possibly of a different species at a
later time. If the stressful conditions persist, the polyp eventually
Zooxanthellae are located within the corals' cytoplasm and
due to the algae's photosynthetic activity, the internal pH of the
coral can be raised; this behavior indicates that the zooxanthellae
are responsible to some extent for the metabolism of their host corals
Corals can be both gonochoristic (unisexual) and hermaphroditic, each
of which can reproduce sexually and asexually. Reproduction also
allows coral to settle in new areas. Reproduction is coordinated by
Life cycles of broadcasters and brooders
Corals predominantly reproduce sexually. About 25% of hermatypic
corals (stony corals) form single sex (gonochoristic) colonies, while
the rest are hermaphroditic.
About 75% of all hermatypic corals "broadcast spawn" by releasing
gametes—eggs and sperm—into the water to spread offspring. The
gametes fuse during fertilization to form a microscopic larva called a
planula, typically pink and elliptical in shape. A typical coral
colony forms several thousand larvae per year to overcome the odds
against formation of a new colony.
A male great star coral, Montastraea cavernosa, releasing sperm into
Synchronous spawning is very typical on the coral reef, and often,
even when multiple species are present, all corals spawn on the same
night. This synchrony is essential so male and female gametes can
meet. Corals rely on environmental cues, varying from species to
species, to determine the proper time to release gametes into the
water. The cues involve temperature change, lunar cycle, day length,
and possibly chemical signalling. Synchronous spawning may form
hybrids and is perhaps involved in coral speciation. The immediate
cue is most often sunset, which cues the release. The spawning
event can be visually dramatic, clouding the usually clear water with
Brooding species are most often ahermatypic (not reef-building) in
areas of high current or wave action. Brooders release only sperm,
which is negatively buoyant, sinking on to the waiting egg carriers
who harbor unfertilized eggs for weeks. Synchronous spawning events
sometimes occurs even with these species. After fertilization, the
corals release planula that are ready to settle.
Planula larvae exhibit positive phototaxis, swimming towards light to
reach surface waters, where they drift and grow before descending to
seek a hard surface to which they can attach and begin a new colony.
They also exhibit positive sonotaxis, moving towards sounds that
emanate from the reef and away from open water. High failure rates
afflict many stages of this process, and even though millions of
gametes are released by each colony, few new colonies form. The time
from spawning to settling is usually two to three days, but can be up
to two months. The larva grows into a polyp and eventually becomes
a coral head by asexual budding and growth.
Basal plates (calices) of Orbicella annularis showing multiplication
by budding (small central plate) and division (large double plate)
Aulopora (Devonian) showing initial budding
Within a coral head, the genetically identical polyps reproduce
asexually, either by budding (gemmation) or by dividing, whether
longitudinally or transversely.
Budding involves splitting a smaller polyp from an adult. As the
new polyp grows, it forms its body parts. The distance between the new
and adult polyps grows, and with it, the coenosarc (the common body of
Budding can be intratentacular, from its oral discs,
producing same-sized polyps within the ring of tentacles, or
extratentacular, from its base, producing a smaller polyp.
Division forms two polyps that each become as large as the original.
Longitudinal division begins when a polyp broadens and then divides
its coelenteron (body), effectively splitting along its length. The
mouth divides and new tentacles form. The two polyps thus created then
generate their missing body parts and exoskeleton. Transversal
division occurs when polyps and the exoskeleton divide transversally
into two parts. This means one has the basal disc (bottom) and the
other has the oral disc (top); the new polyps must separately generate
the missing pieces.
Asexual reproduction offers the benefits of high reproductive rate,
delaying senescence, and replacement of dead modules, as well as
Whole colonies can reproduce asexually, forming two colonies with the
same genotype. The possible mechanisms include fission, bailout and
fragmentation. Fission occurs in some corals, especially among the
family Fungiidae, where the colony splits into two or more colonies
during early developmental stages. Bailout occurs when a single polyp
abandons the colony and settles on a different substrate to create a
new colony. Fragmentation involves individuals broken from the colony
during storms or other disruptions. The separated individuals can
start new colonies.
Locations of coral reefs around the world
Coral reef fish and List of reefs
Many corals in the order
Scleractinia are hermatypic, meaning that
they are involved in building reefs. Most such corals obtain some of
their energy from zooxanthellae in the genus Symbiodinium. These are
symbiotic photosynthetic dinoflagellates which require sunlight;
reef-forming corals are therefore found mainly in shallow water. They
secrete calcium carbonate to form hard skeletons that become the
framework of the reef. However, not all reef-building corals in
shallow water contain zooxanthellae, and some deep water species,
living at depths to which light cannot penetrate, form reefs but do
not harbour the symbionts.
Staghorn coral (
Acropora cervicornis) is an important hermatypic coral
from the Caribbean
There are various types of shallow-water coral reef, including
fringing reefs, barrier reefs and atolls; most occur in tropical and
subtropical seas. They are very slow-growing, adding perhaps one
centimetre (0.4 in) in height each year. The Great Barrier Reef
is thought to have been laid down about two million years ago. Over
time, corals fragment and die, sand and rubble accumulates between the
corals, and the shells of clams and other molluscs decay to form a
gradually evolving calcium carbonate structure.
Coral reefs are
extremely diverse marine ecosystems hosting over 4,000 species of
fish, massive numbers of cnidarians, molluscs, crustaceans, and many
Solitary rugose coral (Grewingkia) in three views; Ordovician,
Although corals first appeared in the
Cambrian period, some
542 million years ago, fossils are extremely rare until the
Ordovician period, 100 million years later, when rugose and tabulate
corals became widespread.
Paleozoic corals often contained numerous
Tabulate corals occur in limestones and calcareous shales of the
Silurian periods, and often form low cushions or
branching masses of calcite alongside rugose corals. Their numbers
began to decline during the middle of the
Silurian period, and they
became extinct at the end of the
Permian period, 250 million
Rugose or horn corals became dominant by the middle of the Silurian
period, and became extinct early in the
Triassic period. The rugose
corals existed in solitary and colonial forms, and were also composed
The scleractinian corals filled the niche vacated by the extinct
rugose and tabulate species. Their fossils may be found in small
numbers in rocks from the
Triassic period, and became common in the
Jurassic and later periods. Scleractinian skeletons are composed
of a form of calcium carbonate known as aragonite. Although they
are geologically younger than the tabulate and rugose corals, the
aragonite of their skeletons is less readily preserved, and their
fossil record is accordingly less complete.
Timeline of the major coral fossil record and developments from 650
m.y.a. to present.
At certain times in the geological past, corals were very abundant.
Like modern corals, these ancestors built reefs, some of which ended
as great structures in sedimentary rocks. Fossils of fellow
reef-dwellers algae, sponges, and the remains of many echinoids,
brachiopods, bivalves, gastropods, and trilobites appear along with
coral fossils. This makes some corals useful index fossils. Coral
fossils are not restricted to reef remnants, and many solitary fossils
may be found elsewhere, such as Cyclocyathus, which occurs in
Gault clay formation.
Main article: Environmental issues with coral reefs
A healthy coral reef has a striking level of biodiversity in many
forms of marine life.
Coral reefs are under stress around the world. In particular,
coral mining, agricultural and urban runoff, pollution (organic and
inorganic), overfishing, blast fishing, disease, and the digging of
canals and access into islands and bays are localized threats to coral
ecosystems. Broader threats are sea temperature rise, sea level rise
and pH changes from ocean acidification, all associated with
greenhouse gas emissions. In 1998, 16% of the world's reefs died
as a result of increased water temperature.
Approximately 10% of the world's coral reefs are dead.
About 60% of the world's reefs are at risk due to human-related
activities. The threat to reef health is particularly strong in
Southeast Asia, where 80% of reefs are endangered. Over 50% of the
world's coral reefs may be destroyed by 2030; as a result, most
nations protect them through environmental laws.
In the Caribbean and tropical Pacific, direct contact between
~40–70% of common seaweeds and coral causes bleaching and death to
the coral via transfer of lipid-soluble metabolites. Seaweed and
algae proliferate given adequate nutrients and limited grazing by
herbivores such as parrotfish.
Water temperature changes of more than 1–2 °C
(1.8–3.6 °F) or salinity changes can kill some species of
coral. Under such environmental stresses, corals expel their
Symbiodinium; without them coral tissues reveal the white of their
skeletons, an event known as coral bleaching.
Submarine springs found along the coast of Mexico's Yucatán Peninsula
produce water with a naturally low pH (relatively high acidity)
providing conditions similar to those expected to become widespread as
the oceans absorb carbon dioxide. Surveys discovered multiple
species of live coral that appeared to tolerate the acidity. The
colonies were small and patchily distributed, and had not formed
structurally complex reefs such as those that compose the nearby
Mesoamerican Barrier Reef System.
Coral reef protection
Marine Protected Areas (MPAs), Biosphere reserves, marine parks,
national monuments world heritage status, fishery management and
habitat protection can protect reefs from anthropogenic damage.
Many governments now prohibit removal of coral from reefs, and inform
coastal residents about reef protection and ecology. While local
action such as habitat restoration and herbivore protection can reduce
local damage, the longer-term threats of acidification, temperature
change and sea-level rise remain a challenge.
To eliminate destruction of corals in their indigenous regions,
projects have been started to grow corals in non-tropical
Relation to humans
Local economies near major coral reefs benefit from an abundance of
fish and other marine creatures as a food source. Reefs also provide
recreational scuba diving and snorkeling tourism. These activities can
damage coral but international projects such as
Green Fins that
encourage dive and snorkel centres to follow a Code of Conduct have
been proven to mitigate these risks.
Live coral is highly sought after for aquaria. Soft corals are easier
to maintain in captivity than hard corals.
6-strand necklace, Navajo (Native American), ca. 1920s, Brooklyn
Corals' many colors give it appeal for necklaces and other jewelry.
Intensely red coral is prized as a gemstone. Sometimes called fire
coral, it is not the same as fire coral. Red coral is very rare
because of overharvesting.
Always considered a precious mineral, "the Chinese have long
associated red coral with auspiciousness and longevity because of its
color and its resemblance to deer antlers (so by association, virtue,
long life, and high rank". It reached its height of popularity
during the Manchu or Qing Dynasty (1644-1911) when it was almost
exclusively reserved for the emperor's use either in the form of coral
beads (often combined with pearls) for court jewelry or as decorative
Penjing (decorative miniature mineral trees).
Coral was known as
shanhu in Chinese. The "early-modern 'coral network' [began in] the
Mediterranean Sea [and found its way] to Qing China via the English
East India Company". There were strict rules regarding its use in
a code established by the
Qianlong Emperor in 1759.
Depiction of coral in the Juliana Anicia Codex, a copy, written in
Constantinople in 515 AD, of Dioscorides' 1st century AD Greek work.
The facing page states that coral can be used to treat ulcers.
In medicine, chemical compounds from corals are used to treat cancer,
AIDS and pain, and for other uses.
Coral skeletons, e.g.
also used for bone grafting in humans.
Coral Calx, known as Praval
Bhasma in Sanskrit, is widely used in traditional system of Indian
medicine as a supplement in the treatment of a variety of bone
metabolic disorders associated with calcium deficiency. In
classical times ingestion of pulverized coral, which consists mainly
of the weak base calcium carbonate, was recommended for calming
stomach ulcers by
Galen and Dioscorides.
Tabulate coral (a syringoporid); Boone limestone (Lower Carboniferous)
near Hiwasse, Arkansas, scale bar is 2.0 cm.
Coral reefs in places such as the East African coast are used as a
source of building material. Ancient (fossil) coral limestone,
notably including the
Coral Rag Formation
Coral Rag Formation of the hills around Oxford
(England), was once used as a building stone, and can be seen in some
of the oldest buildings in that city including the Saxon tower of St
Michael at the Northgate, St. George's Tower of
Oxford Castle, and the
mediaeval walls of the city.
Annual growth bands in some corals, such as the deep sea bamboo corals
(Isididae), may be among the first signs of the effects of ocean
acidification on marine life. The growth rings allow geologists to
construct year-by-year chronologies, a form of incremental dating,
which underlie high-resolution records of past climatic and
environmental changes using geochemical techniques.
Certain species form communities called microatolls, which are
colonies whose top is dead and mostly above the water line, but whose
perimeter is mostly submerged and alive. Average tide level limits
their height. By analyzing the various growth morphologies,
microatolls offer a low resolution record of sea level change.
Fossilized microatolls can also be dated using Radiocarbon dating.
Such methods can help to reconstruct
Holocene sea levels.
Increasing sea temperatures in tropical regions (~1 degree C) the last
century have caused major coral bleaching, death, and therefore
shrinking coral populations since although they are able to adapt and
acclimate, it is uncertain if this evolutionary process will happen
quickly enough to prevent major reduction of their numbers.
Though coral have large sexually-reproducing populations, their
evolution can be slowed by abundant asexual reproduction. Gene
flow is variable among coral species. According to the
biogeography of coral species gene flow cannot be counted on as a
dependable source of adaptation as they are very stationary organisms.
Also, coral longevity might factor into their adaptivity.
However, adaptation to climate change has been demonstrated in many
cases. These are usually due to a shift in coral and zooxanthellae
genotypes. These shifts in allele frequency have progressed toward
more tolerant types of zooxanthellae. Scientists found that a
certain scleractinian zooxanthella is becoming more common where sea
temperature is high. Symbionts able to tolerate warmer water
seem to photosynthesise more slowly, implying an evolutionary
In the Gulf of Mexico, where sea temperatures are rising,
cold-sensitive staghorn and elkhorn coral have shifted in
location. Not only have the symbionts and specific species been
shown to shift, but there seems to be a certain growth rate favorable
to selection. Slower-growing but more heat-tolerant corals have become
more common. The changes in temperature and acclimation are
complex. Some reefs in current shadows represent a refugium location
that will help them adjust to the disparity in the environment even if
eventually the temperatures may rise more quickly there than in other
locations. This separation of populations by climatic barriers
causes a realized niche to shrink greatly in comparison to the old
Corals are shallow, colonial organisms that integrate δ18O and trace
elements into their skeletal aragonite (polymorph of calcite)
crystalline structures, as they grow.
Geochemistry anomalies within
the crystalline structures of corals represent functions of
temperature, salinity and oxygen isotopic composition. Such
geochemical analysis can help with climate modeling.
Strontium/calcium ratio anomaly
Time can be attributed to coral geochemistry anomalies by correlating
strontium/calcium minimums with sea surface temperature (SST) maximums
to data collected from NINO 3.4 SSTA.
Oxygen isotope anomaly
The comparison of coral strontium/calcium minimums with sea surface
temperature maximums, data recorded from NINO 3.4 SSTA, time can be
correlated to coral strontium/calcium and δ18O variations. To confirm
accuracy of the annual relationship between Sr/Ca and δ18O
variations, a perceptible association to annual coral growth rings
confirms the age conversion.
Geochronology is established by the
blending of Sr/Ca data, growth rings, and stable isotope data. El
Nino-Southern Oscillation (ENSO) is directly related to climate
fluctuations that influence coral δ18O ratio from local salinity
variations associated with the position of the South Pacific
convergence zone (SPCZ) and can be used for ENSO modeling.
Sea surface temperature
Sea surface temperature and sea surface salinity
Global sea surface temperature (SST)
The global moisture budget is primarily being influenced by tropical
sea surface temperatures from the position of the Intertropical
Convergence Zone (ITCZ). The
Southern Hemisphere has a unique
meteorological feature positioned in the southwestern Pacific Basin
called the South Pacific Convergence Zone (SPCZ), which contains a
perennial position within the Southern Hemisphere. During ENSO warm
periods, the SPCZ reverses orientation extending from the equator down
south through Solomon Islands, Vanuatu,
Fiji and towards the French
Polynesian Islands; and due east towards
South America affecting
geochemistry of corals in tropical regions.
Geochemical analysis of skeletal coral can be linked to sea surface
salinity (SSS) and sea surface temperature (SST), from El Nino 3.4
SSTA data, of tropical oceans to seawater δ18O ratio anomalies from
corals. ENSO phenomenon can be related to variations in sea surface
salinity (SSS) and sea surface temperature (SST) that can help model
tropical climate activities.
Limited climate research on current species
Climate research on live coral species is limited to a few studied
Porites coral provides a stable foundation for
geochemical interpretations that is much simpler to physically extract
data in comparison to
Platygyra species where the complexity of
Platygyra species skeletal structure creates difficulty when
physically sampled, which happens to be one of the only multidecadal
living coral records used for coral paleoclimate modeling.
Main article: Reef aquarium
This dragon-eye zoanthid is a popular source of color in reef tanks
The saltwater fishkeeping hobby has expanded, over recent years, to
include reef tanks, fish tanks that include large amounts of live rock
on which coral is allowed to grow and spread. These tanks are
either kept in a natural-like state, with algae (sometimes in the form
of an algae scrubber) and a deep sand bed providing filtration, or
as "show tanks", with the rock kept largely bare of the algae and
microfauna that would normally populate it, in order to appear
neat and clean.
The most popular kind of coral kept is soft coral, especially
zoanthids and mushroom corals, which are especially easy to grow and
propagate in a wide variety of conditions, because they originate in
enclosed parts of reefs where water conditions vary and lighting may
be less reliable and direct. More serious fishkeepers may keep
small polyp stony coral, which is from open, brightly lit reef
conditions and therefore much more demanding, while large polyp stony
coral is a sort of compromise between the two.
Main article: Aquaculture of coral
Coral aquaculture, also known as coral farming or coral gardening, is
the cultivation of corals for commercial purposes or coral reef
restoration. Aquaculture is showing promise as a potentially effective
tool for restoring coral reefs, which have been declining around the
world. The process bypasses the early growth stages of
corals when they are most at risk of dying.
Coral fragments known as
"seeds" are grown in nurseries then replanted on the reef. Coral
is farmed by coral farmers who live locally to the reefs and farm for
reef conservation or for income. It is also farmed by scientists for
research, by businesses for the supply of the live and ornamental
coral trade and by private aquarium hobbyists.
Further images: commons:Category:
Coral reefs and
Fungia sp. skeleton
Polyps of Eusmilia fastigiata
Pillar coral, Dendrogyra cylindricus
Brain coral, Diploria labyrinthiformis
Brain coral spawning
Brain coral releasing eggs
Fringing coral reef off the coast of Eilat, Israel.
^ Hoeksema, Bert (2015). "Octocorallia". World Register of Marine
Species. Retrieved 2015-04-24.
^ Hoeksema, Bert (2015). "Hexacorallia". World Register of Marine
Species. Retrieved 2015-04-24.
^ Hoeksema, Bert (2016). "Ceriantharia". World Register of Marine
Species. Retrieved 2017-02-04.
^ Squires, D.F. (1959). "
Deep sea corals collected by the Lamont
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