The Great Barrier Reef is the only living organic collective that can be seen from space. It is the largest coral reef ecosystem and lies off the east coast of Australia. The coral forming the Great Barrier Reef has caused many ships to sink, including Captain James Cooks ship the Endeavour and HMS Pandora in 1791.
Although coral can be found anywhere in the world, it is most abundant in the tropics. This is because it likes warm shallow water, where there is plenty of light and water movement and a high salt content. Coral feed mainly at night on plankton and reproduce in various ways. Some split from original polyp. Other's fertilize their eggs internally and then release them as planulae. Finally some shed their eggs and sperm into the water usually all at the same time to increase success.
Coral consists of tiny creatures called polyps. They live inside a shell made of aragonite, which is a type of calcium carbonate. It is this hard shell we recognize as coral. Dead coral is white as only live coral is colored. This is because of a single cell algae called zooxanthellae, which live inside the coral tissue and produce organic carbon.
Numerous types of coral live in coral reefs. The main building blocks of reefs are hard calcareous skeletons called True stony corals. These are produced by the polyps themselves. Gorgonians commonly known as sea fans or sea whips are very strong plant like growths with a horny skeleton running along the inside stem. Soft corals have jelly like bodies and tentacles.
The biggest threat to coral reefs come from humans. Pollution and rising water temperatures causes bleaching. This is where the coral expels its zooxanthellae and begins to starve. It will also lose its color and go white. The water temperature only has to increase by one and a half to two degrees Celsius, for six to eight weeks for bleaching to occur. If conditions return to normal it may survive, but growth will be stunted. Another problem is fishing for aquariums and ornaments. The only threat to coral that is not of the human kind is the Crown Of Thorns starfish which is a predator.