Understanding Coral Reefs

[http://blog.stevenwsmeltzer.com/what-are-coral-reefs/ Coral reefs] are made up of  tiny animals that belong to the class anthozoans, the major class of organisms within the phylum cnidaria (the "c" is silent). Cnidaria has more than 6,000 recognized species of sea fans, sea pansies, jellyfish, and sea anemones. Corals, after their larvae phase, aren't mobile but rather stay fixed in a single place.  This type of animal is called a sessile animal.

[http://www.stevenwsmeltzer.com Coral reef] colonies are composed of millions of these tiny, cup-shaped animals termed polyps. A single coral polyp might be as large as a saucer or smaller than the head of a pin. Millions of polyps functioning in concert in a cooperative colony generation after generation create the limestone skeletons that form the framework of the wonderful coral reef. Corals begin life in tropical waters as free-floating larvae. After a relatively short period of time, the larva eventually attaches itself to a hard surface and becomes a polyp. Coral reef colonies reproduce both sexually and asexually. In sexual reproduction, the coral polyps discharge both eggs and sperm into the water. (This is also known as coral spawning.) One kind of asexual reproduction takes place when fragments of coral are broken off as a result of storm action. The broken pieces of corals usually survive and continue to grow and make a new colony. This process is referred to as "fragmentation". Corals exist in colonies consisting of numerous individuals, each of which is called polyp. They secrete a hard calcium carbonate (rock-like) skeleton, which serves as a uniform foundation or substrate for the colony. This skeleton enables two fundamental functions, first for the coral itself it provides fortification, as the polyps can contract into the structure if predators approach and second this same skeletal construction is what makes up the coral reefs over time. The calcium carbonate is secreted at the bottom of the polyps, consequently the living portion of the coral colony occurs at the exterior of the skeletal structure, totally covering it. The calcium carbonate deposited by the living colony incessantly adds to the size of the general structure and consequently the growth of the reef. The expansion of these reef structures varies widely, based on the varieties of coral and environmental conditions-- ranging from 0.3 to 10 centimeters per year. Different varieties of coral assemble structures of various sizes and shapes such as brain corals, fan corals, encrusting corals, etc., producing amazing variety and complexity in the coral reef ecosystem. Different coral species tend to be segregated into characteristic zones on a reef, separated out by competition with other species and by environmental conditions. The skeletons of stony corals are secreted by the lower part of the polyp. This process produces a cup, known as the calice, in which the polyp is located. The walls encircling the cup are known as the theca, and the base is known as the basal plate. Thin, calcareous septa (sclerosepta), that provides structural integrity, armor, and an increased surface area for the polyp's soft tissues, extend upward from the basal plate and branch inward from its external wall. Periodically, a polyp will lift off its base and exude a new floor or base to its cup, forming a new basal plate above the previous one. This produces a minute chamber in the skeleton. If polyps are physically stressed or under probable attack, they move down into the calice so that practically no portion is exposed above the skeletal platform. This protects the organism from predators and the elements (Barnes, R.D., 1987; Sumich, 1996). Corals contain only a limited degree of organ development and consists of three fundamental tissue layers: an outer layer or epidermis, an inner layer of cells lining the gastrovascular cavity (an internal space for digestion) and a layer called the mesoglea between the other two layers Barnes, R.D., 1987. Corals feed by reaching out by means of tentacles to seize prey such as small fish and planktonic creatures (any drifting organisms, animal, plant, archaea or bacteria that inhabit the pelagic zone of the oceans). See Also: Creatures of the Coral Reefs Resources: Marine Species Galleries: Coral Reef Images Pictures of Fish Sea Turtles Crustaceans and Echinoderms Moray Eels Detailed Information on select Marine Species: Caribbean Fish Hawaiian Fish Sponges Crustaceans, Invertebrates, Mollusks, Echinoderms