The coral reef is the most delicate and complex ecosystem on Earth. Coral is an animal, although it much resembles an inert rock. Coral is a colonial population of polyps, similar to jellyfish except they are stationary. The polyps are simple, comprised of a group of tentacles, a mouth and a digestive gut. They have the ability to adsorb calcium and carbonate from seawater to build their exoskeleton, which consist of calcium carbonate. This accumulation of exoskeletons produce the coral reef, which are in fact a rock, limestone, but in fact are both are the result of a symbiotic relationships between organic and inorganic chemistry.
Coral polyps start life as free floaters in the sea, eventually attaching themselves to a solid surface. They reproduce both asexually and sexually by releasing eggs and sperm into the sea, called coral spawning. The reefs themselves are divided into three main categories. The fringing reef are those which are proximal to the shoreline on the continental shelf. Barrier reefs are separated from the mainland by a deep lagoon, and serve to protect the mainland from the sea. The largest reef system in the world is this type, being the Great Barrier Reef of Australia.
The third type of reef are the Atolls. These are rings of reefs surrounding volcanic islands. As the volcano exhaust it’s fuel it sinks, leaving these growing reefs remaining. There are over 300 atolls in the South Pacific. All of these reef types contain both hard and soft coral. Hard coral produces the calcium carbonate exoskeleton, where soft corals do not. Hard corals have multiples of six tentacles. Soft corals tend to form plant like appearances, resembling many algae species. They typically have eight tentacles per polyp.
One of the unique characteristics of coral reefs are the symbiotic relationship with a certain species of algae, the zooxanthellae. Most corals feed on plankton, however sugars produced by the zooxanthellae via photosynthesis also provide sugars for nutrient. This type of symbiotic relationship is called mutualism, whereby both the coral and algae benefit one another. The coral supplies shelter, whereby the algae supplies food. The only predators to the coral reef are certain species of fish, such as the parrot fish, certain mollusk and some starfish species. The largest danger to the reefs are warming global temperatures and pollution.
Coral Reefs and Tropical Rain Forest are responsible, by some analyst, for nearly 90% of the Earth’s oxygen levels in our atmosphere, both ecosystems disappearing at an alarming rate due to demographic development and destruction of habitat.