Coral reefs are among the most diverse and productive communities on Earth. They are found in the warm, clear, shallow waters of tropical oceans worldwide. Reefs have functions ranging from providing food and shelter to fish and invertebrates, to protecting the shore from erosion.
Although many corals resemble plants, they are actually members of the animal phylum Cnidaria. Most corals are colonial, which means that each coral is made up of many individual polyps connected by living tissue (the coenosarc). Each polyp has a cup-like shape with a ring of tentacles around a central opening (pharynx) that functions as both mouth and anus. The tentacles are tipped with stinging cells called nematocysts. Corals use the nematocysts to defend themselves and to capture prey. The body wall consists of three cell layers: the outer or ectoderm, the middle or mesoderm, and the inner or endoderm. There is no skeleton inside the polyp itself. Instead, the polyps sit on top of an external skeleton that is made from the polyp’s secretions.
One of the most interesting findings about coral are some of their reproducing habits. Horn coral, for example, depend on waves to break off pieces and carry them to new locations where the broken pieces start new colonies. The more famous coral forms
huge deposits that take on the shape of small, underwater mountains of calcium carbonate. Corals are benthic organisms in the fact that they are stationary for the most part, and do not swim or drift in the ocean. All coral feed on plankton. Soft coral are filter feeders, filtering out plankton as the current passes through the porous structure of the coral. Hard coral have tiny critters located inside a limestone shell that rely on plankton that float by as their food source.
Since they are very sensitive, coral require a very specific environment in order to survive. They are found generally in warm, shallow areas of the tropical oceans. Although they are best developed in temperatures from about twenty-three to twenty-five degrees Celsius, coral reefs can be found in temperatures as low as eighteen degrees Celsius. Corals are restricted to seawater with a salinity ranging from thirty to forty parts per thousand. They also require a concentrated amount of calcium carbonate to assist in the process of forming their skeleton. The shape, size and structure of the coral are directly related to their location in the ocean, and depth. Coral located near the surface tend to be flexible in order to flex and sway with the wave action and tidal currents. The water currents and wind can also play an important role in the development of coral reefs. The water currents shape and mold the coral, and the wind both affects the currents and shapes the coral when it rises above the water to form small islands called cays. Because of their sensitivity, almost any adverse changes to the environment can result in death. For example, a reef on Stone Island, near Australia, was killed to a depth of three
meters below mean tide level after a week of hurricane type rains swept through the region.
Many different types of animals find shelter in coral reefs: fish, crustaceans, and sponges, not to mention the corals themselves. The many nooks and crevices in the reefs provide a perfect hiding place for almost all types of sea creatures. Sponges, for instance, attach themselves to the coral for protection from predators. On the other hand, a moray eel will take residence in one of the holes in the reef to lie in wait for prey. Some of the other animals that live in coral reefs include giant clams, crabs, Christmas tree worms, feather duster worms, shrimp, and various plants.
Coral reefs are huge, living, ecosystems that provide food and shelter to many harboring creatures. Not only does this symbiotic relationship orchestrate harmony in the ocean, but corals also provide land animals with a defense mechanism against powerful storms and erosive tides. Although coral reefs make up less than 1% of the Earths surface, their non-existence would be detrimental.