Coral reefs
This article describes the habitat of the coral reefs. It is one of the sub-categories within the section dealing with biodiversity of marine habitats and ecosystems. It gives an overview of the formation, distribution, biology, zonation, requirements for development, biota and threats.
Introduction
Coral reefs are one of the most diverse ecosystems in the world. The organisms are part of the group Cnidaria. The most known type of corals is the one in the clear, warm tropical water with plenty of colorful fishes. This is a stony, shallow water type. The clear water is because of the low concentrations of nutrients. But there are also deep water corals that live in dark cold waters and soft corals that live in shallow, cold waters. They are organically constructed, wave resistant rock structures created by carbonate-secreting animals and plants.
Formations
The formation begins when free-swimming coral larvae attach to submerged rocks or other hard substrates along the edges of islands or continents. The reef expands and will form an atoll, barrier or fringing. These 3 are the main reef types. Atolls are circular or oval coral reefs that encircle a lagoon partially or completely. A barrier reef is a reef that borders the shoreline over a long distance. They are separated from the adjacent land mass by a lagoon. Further, a fringing reef forms borders along the shoreline and the surrounding islands, but at smaller distance than barrier reefs. It is directly attached to the land. This is the most common type of coral reefs. [2] Other special reef arrangements are apron, patch, ribbon, table and bank reefs. Apron reefs are very similar to fringing reefs. They are more gently sloping and extending downward from the land margin. Patch reefs are isolated and often circular. They surround a lagoon or embayment. Ribbon reefs are small and long and are connected to an atoll lagoon. Table reefs are future atolls, but are not yet connected to a lagoon. At last, bank reefs are similar to the patch, but are larger and often hemispherical. [3]
Coral reefs are also one of the oldest habitats in the ocean. They have slow growth rates so it can take up to 10,000 years for a coral reef to form from a group of larvae. [4] The different types all share similarities in their biogeographic profiles. Horizontal and vertical '''zonation''' is created by bottom topography, depth, wave and current strength, light, temperature and suspended sediments.
Distribution
The warm water corals are distributed in the tropics. They are found in areas where the water is more than 18°C and where the water is clear. The maximum average depth is 60 meters, but other types can be found deeper. They are generally found within the 30°N and 30°S. Various species are found in all oceans of the world, from the tropics to the polar regions. Cold water corals have been found in places as Antartica, Australia, Canada, Ecuador, Japan, New Zealand, Norway, United Kingdom, Europe and the United States.
References
- ↑ http://en.wikipedia.org/wiki/Coral_reef
- ↑ NOAA National Ocean Service Education: Corals
- ↑ http://www.coral-reefs.org
- ↑ Barnes R.D. 1987. Invertebrate Zoology. Fifth edition. Fort Worth, TX. Harcourt Brace Jovanovich College Publishers. 92-96, 127-134, 149-162.
- ↑ 5.0 5.1 5.2 5.3 http://www.coral-reefs.org
- ↑ http://antigreen.blogspot.com/2006_09_01_archive.html
- ↑ http://maps.grida.no/go/graphic/distribution-of-coldwater-and-tropical-coral-reefs - UNEP/GRID-Arendal - Hugo Ahlenius
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