Coral island
A coral island is a type of
Ecosystem
Coral reefs are some of the oldest ecosystems on the planet, over geological time, they form massive reefs of limestone. The reef environment supports more plant and animal species than any other habitat.[3][4] Coral reefs are vital for life in multiple aspects some of which include structure, ecology, and nutrient cycles which all support biodiversity in the reefs.
Coral reefs build massive calcareous 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, 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.[5]
Formation
A coral island begins as a
Once the island is submerged, the coral must keep growing to stay in the epipelagic zone. This causes the coral to grow into an atoll with a shallow lagoon in the middle. The lagoon undergoes accretion and creates an island completely made of carbonate materials. The process is later enhanced with the remains of plant life which grows on the island.[6]
Low vs. high island
The term "low island" refers to geologic origin rather than a strict classification of height. Some low islands, such as Banaba, Makatea, Nauru, and Niue, rise several hundred feet above sea level, while numerous high islands (those of volcanic origin) rise a few feet above sea level, often classified as "rocks". Low islands ring the lagoons of atolls. The two types of islands are often found in proximity to each other. This is especially the case among the islands of the South Pacific Ocean, where low islands are found on the fringing reefs that surround most high islands.[citation needed]
Distribution
Most of the world's coral islands are in the
Ecology
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. Through chemical and physical changes humans can cause significant harm to reef systems and slow the creation of coral island chains.[5]
Coral reefs are threatened by numerous
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.
Although low islands may have fewer potential habitats than high islands, thus lower species diversity, studies of both types of islands in Palau found that species diversity, at least in the waters around the island, is more affected by island size than by its origin.[9]
Climate and habitability
Low islands have poor, sandy soil and little fresh water, which makes them difficult to farm. They cannot support human habitation as well as high islands. They are also threatened by
-
The Moruroa atoll, composed of low islands on the reef encircling a central lagoon
See also
References
- ^ "coral island". Encyclopædia Britannica. Retrieved 2012-12-26.
- JSTOR 210643.
- ISBN 978-0-632-02983-9.
- ^ Fuchs. T (2013). "Effects of Coral Reef Complexity on Invertebrate Biodiversity". Immediate Science Ecology Publishing: 1–10. Archived from the original on April 2, 2015.
- ^ ISBN 978-0002164429.
- ISBN 978-0816048748.
- S2CID 11831104.
- ISSN 0003-1569.
- ISSN 0378-1909.
External links
- Micronesian culture: High island and low island cultures at Britannica.com. Retrieved 2011-09-22.