Coral and Coral Reef - The Builders: Corals And Coralline Algae, Biology Of Corals, Coral Reef Distribution, Environmental Setting And Requirements
organisms reefs marine
Coral reefs are highly diverse ecosystems, supporting greater numbers of fish species and other organisms than any other marine ecosystem. Coral reefs are located in warm, shallow, tropical marine waters with enough light to stimulate the growth of the reef organisms. The primary reef-building organisms are invertebrate animals known as corals; corals secrete the bulk of the calcium carbonate (limestone) that makes up the inorganic reef structure, along with material deposited by coralline algae, mollusks, and sponges.
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Corals are small (0.06–0.5 in; 1.5–12 mm), colonial, marine invertebrates. They belong to the class Anthozoa, phylum Cnidaria (or Coelenterata). Corals are subdivided into (1) stony corals (reef-building or hermatypic)—order Scleractinia, subclass Hexacorallia—which have six tentacles, and (2) soft corals, sea fans, and sea whips—order Gorgonacea, subclass Octoco…
Adult corals are benthic (bottom-dwelling), sessile (attached) animals usually found in single-species colonies. These colonies may house hundreds or thousands of polyps. The polyps are joined to one another by a thin tissue layer called the coenosarc (pronounced SEE-na-sark). The coenosarc connects the entire coral colony and covers the underlying coral skeleton. Reproduction through an asexual b…
Although corals live in nearly all marine environments, hermatypic corals thrive in a rather narrow set of environmental conditions. These limitations also restrict the geographic distribution of well-developed coral reef tracts. Coral reefs typically occur in water depths less than 190–230 ft (60–70 m) and maximum growth rates occur at depths less than 60 ft (18 m). This is because …
Reefs tend to develop a definite depth profile and associated coral zonation under the influence of constant wave activity. This results from the decrease in wave energy with water depth. The reef crest is the shallowest reef area and subject to the highest wave energy; here coral and algae encrust the substrate to avoid being broken and swept away. The reef crest is located at the top of the seaw…
In addition to the environmental requirements for coral growth described above, other factors play a role in coral reef character over long time intervals, that is, during geologic time spans. The two most important controls are both related to water depth—sea level change and crustal movement. World-wide fluctuations in sea level can be caused by volume changes of fresh water in global res…
Coral reefs around the world have similar plants and animals. This means that the same families and genera tend to be present, although the actual species may be different. They have the highest biodiversity and greatest ecological complexity of any marine ecosystem. Many coral-reef organisms have established balanced, mutualistic relationships that help sustain a great richness of species and a t…
As an underwater environment, coral reefs offer a wide variety of habitats for plants and animals. Phytoplankton, benthic algae, and bacteria are at the base of the food web. They serve as food for the large variety of animals in the coral-reef ecosystem. If you ever visit a coral reef, you may find that greenery seems relatively scarce; however, six inconspicuous types of plants make coral reefs …
Coral reefs are sometimes disturbed by natural forces, such as extreme rain events that dilute seawater, waves associated with hurricane-force winds, volcanism, earthquakes, and thermal stress from unusually warm water (such as El Niño events). These natural conditions rarely destroy entire reefs, and the ecosystem can recover over time. The crown-of-thorns starfish (Acanthaster planci) has…
Corals reefs provide extremely valuable environmental services for people, including the protection of shorelines from the full onslaught of storm-driven waves. Some of these services are of direct economic benefit to people, and they could be used on a sustained-yield basis, for example, through ecotourism or a controlled fishery. Coral reefs serve as a natural laboratory where biologists are eng…
Regrettably, many human uses of coral reefs damage their physical and ecological structure. The most devastating direct damage is caused by mining of reefs to provide calcium-based material for the construction of buildings, including the manufacturing of cement. Although fishing is a potentially sustainable activity, it is not often practiced as one. The most destructive fishing technique used in…
Although coral reefs may be suffering a variety of ills, there is still hope. In the 1980s and 1990s, many countries began to realize the importance of coral reefs and to act accordingly. In response to requests from marine scientists for increased monitoring of reef condition, along with calls from environmental activists for enhanced reef conservation, several countries developed management plan…
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