![Diamonds Thudufushi Beach and Water Villas, May 2017 -08](https://upload.wikimedia.org/wikipedia/commons/3/32/Diamonds_Thudufushi_Beach_and_Water_Villas%2C_May_2017_-08.jpg)
A coral island is a type of
island
An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...
formed from
coral
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...
detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
and associated organic material.
It occurs in tropical and sub-tropical areas, typically as part of a
coral reef
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, whose polyps cluster in groups.
Co ...
which has grown to cover a far larger area under the sea.
Ecosystem
![Coral reef at palmyra](https://upload.wikimedia.org/wikipedia/commons/d/d0/Coral_reef_at_palmyra.jpg)
Coral reefs are some of the oldest ecosystems on the planet, over geological time forming massive reefs of
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
. The reef environment supports more plant and animal species than any other habitat.
Coral reefs are vital for life for multiple aspects some of which include structure, ecology, and nutrient cycles which all support
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
in the reefs.
Coral reefs build massive
calcareous
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
In zoology
''Calcareous'' is used as an adje ...
skeletons that serve as homes for animals such as fish hiding inside the crooks and crannies of the reef and barnacles attaching themselves directly to the coral’s structure. The structures also help plants that need the sun to
photosynthesize
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in c ...
, by lifting the plants to the ocean’s surface where the sunlight can penetrate the water. The structures also create calm zones in the ocean providing a place for fish and plant species to thrive.
Over geological time a reef may reach the surface and can become a coral island, where it begins a whole new ecosystem for land-based creatures.
Formation
![Coral atoll formation animation](https://upload.wikimedia.org/wikipedia/commons/d/d8/Coral_atoll_formation_animation.gif)
A coral island begins as a
volcanic island
Geologically, a high island or volcanic island is an island of volcanic origin. The term can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed ...
over a
hot spot
Hotspot, Hot Spot or Hot spot may refer to:
Places
* Hot Spot, Kentucky, a community in the United States
Arts, entertainment, and media Fictional entities
* Hot Spot (comics), a name for the DC Comics character Isaiah Crockett
* Hot Spot (Tra ...
. As the volcano emerges from the sea, a
fringing reef
A fringing reef is one of the three main types of coral reef. It is distinguished from the other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows direc ...
grows on the outskirt of the volcano. The volcano eventually moves off of the hot spot through a process known as
plate tectonics
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...
. Once this occurs the volcano can no longer keep up with the wave
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
and undergoes
subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...
.
Once the island is submerged, the coral must keep growing to stay in the
epipelagic zone
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
. This causes the coral to grow into an
atoll
An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gr ...
with a shallow
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...
in the middle. The lagoon can then undergo
accretion
Accretion may refer to:
Science
* Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity
* Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...
and create an island completely made of
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...
materials. The process is later enhanced with the remains of plant life which grows on the island.
Distribution
Most of the world's coral islands are in the
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
. The American
territories
A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal.
In international politics, a territory is usually either the total area from which a state may extract power resources or an ...
of
Jarvis,
Baker
A baker is a tradesperson who bakes and sometimes sells breads and other products made of flour by using an oven or other concentrated heat source. The place where a baker works is called a bakery.
History
Ancient history
Since grains ha ...
and
Howland Island
Howland Island () is an uninhabited coral island located just north of the equator in the central Pacific Ocean, about southwest of Honolulu. The island lies almost halfway between Hawaii and Australia and is an unorganized, unincorporated ter ...
s are clear examples of coral islands. The
Lakshadweep Islands
Lakshadweep (), also known as Laccadives (), is a union territory of India. It is an archipelago of 36 islands in the Arabian sea, located off the Malabar Coast.
The name ''Lakshadweep'' means "one lakh islands" in Sanskrit, though the Lac ...
union territory of
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
is a group of 39 coral Islands, along with some minor
islets
An islet is a very small, often unnamed island. Most definitions are not precise, but some suggest that an islet has little or no vegetation and cannot support human habitation. It may be made of rock, sand and/or hard coral; may be permanent ...
and
banks
A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets.
Because ...
. Some of the
islands belonging to Kiribati
Kiribati (), officially the Republic of Kiribati ( gil, ibaberikiKiribati),[Kiribati]
''The Wor ...
are considered coral islands. The
Maldives
Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje, ), officially the Republic of Maldives ( dv, ދިވެހިރާއްޖޭގެ ޖުމްހޫރިއްޔާ, translit=Dhivehi Raajjeyge Jumhooriyyaa, label=none, ), is an archipelag ...
consist of coral islands.
St. Martin's Island
Saint Martin Island ( bn, সেন্টমার্টিন দ্বীপ) is a small island (area only 3 km2) in the northeastern part of the Bay of Bengal, about 9 km south of the tip of the Cox's Bazar-Teknaf peninsula, and fo ...
is an 8 km
2 coral island located in
Bangladesh
Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the eighth-most populous country in the world, with a population exceeding 165 million people in an area of . Bangladesh is among the mos ...
. Coral islands are located near
Pattaya
Pattaya ( th, พัทยา, , ) is a city in Thailand. It is on the east coast of the Gulf of Thailand, about southeast of Bangkok, within, but not part of, Bang Lamung district in the province of Chonburi province, Chonburi. Pattaya City ( ...
and
Ko Samui
Ko Samui (or Koh Samui, also often locally shortened to Samui; th, เกาะสมุย, ) is an island off the east coast of Thailand. Geographically in the Chumphon Archipelago, it is part of Surat Thani Province, though as of 2012, Ko ...
,
Thailand
Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
.
Ecology
![Bleached coral, Acoropora sp](https://upload.wikimedia.org/wikipedia/commons/4/47/Bleached_coral%2C_Acoropora_sp.jpg)
Coral is important for biodiversity and the growth of fish populations, so maintaining coral reefs is important. Many coral islands are small with low elevation above sea level. Thus they are at threat from storms and
rising sea levels
Rising may refer to:
* Rising, a stage in baking - see Proofing (baking technique)
*Elevation
* Short for Uprising, a rebellion
Film and TV
* "Rising" (''Stargate Atlantis''), the series premiere of the science fiction television program ''Starga ...
. Through chemical and physical changes humans can cause significant harm to reef systems and slow the creation of coral island chains.
Coral reefs are threatened by numerous
anthropogenic
Anthropogenic ("human" + "generating") is an adjective that may refer to:
* Anthropogeny, the study of the origins of humanity
Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows:
* Human im ...
impacts, some of which have already had major effects worldwide.
Reefs grow in shallow, warm, nutrient-poor waters where they are not outcompeted by
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
. By adding fertilizers into the water runoff, phytoplankton populations can explode and choke out coral reef systems. Adding too many sediments can cause a similar problem by blocking out the sun, starving the
zooxanthellae
Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus ''Sy ...
that live on coral causing it to undergo a process known as
coral bleaching
Coral bleaching is the process when corals become white due to various stressors, such as changes in temperature, light, or nutrients. Bleaching occurs when coral polyps expel the zooxanthellae (dinoflagellates that are commonly referred to as alg ...
.
The ocean's acidity is also a factor. Coral is made of calcium carbonate and is dissolved by carbonic acid. With the increase in carbon dioxide from
combustion reactions in the atmosphere through precipitation, carbon dioxide mixes with water and forms
carbonic acid, raising the ocean's acidity which slows coral growth.
See also
*
Raised coral atoll
A raised coral atoll or uplifted coral atoll is an atoll that has been lifted high enough above sea level by tectonic forces to protect it from scouring by storms and enable soils and diverse – often endemic – species of flora and fauna to de ...
References
{{DEFAULTSORT:Coral Island
Atolls
Islands by type