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Threats
Bleaching, pollution,
overfishing, collecting
for jewelry
STATUS:
IUCN -- COMMERCIALLY THREATENED 1994, (including 170
species worldwide)
SIZE:
Varies with species
HABITAT:
Grow best between 65-86 degrees F (18-30 degrees C) in less than 164 feet (50 m). Water must be clear and free of sediment.
POPULATION:
Indeterminate
CURRENT RANGE:
Tropical regions, worldwide no more than 32 degrees North or 27 degrees South of the Equator
CITES trade restrictions
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The Ocean's Rain Forests
Coral reefs are the richest ecosystems in the world's oceans: they host more species of plants and animals than any other marine environment. They are, in effect, the rain forests of the sea.
Reefs are built by tiny organisms called polyps. Coral polyps have hard, cuplike external skeletons that form the body of the coral reef. Only the polyps on the outside layer of a reef are alive; the core of the reef is built of layer upon layer of the hard coral skeletons -- the predecessors of the outermost living layer. It takes millions of individual coral skeletons, built up over thousands of years, to form a coral reef.
The coral polyps on the outside of the reef live in synbiosis with a type of algae called zooxanthellae. These algae live in polyp tissues and use sunlight to produce the oxygen and sugars that are consumed by the coral. The polyps in turn produce carbon dioxide, which the algae use to produce more oxygen and sugars.
Irrevocable Loss
These apparently delicate organisms are surprisingly tough. Coral reefs are well adapted to withstand short-term damage from ocean storms, and even long-term, slow climatic changes. But since the 1980s, scientists have recorded increasingly frequent episodes of coral Òbleaching.Ó When the algae disappear from the coral polyps, the reef loses its color and looks bleached. Losing their symbiotic partners can mean death for the polyps; and if the polyps die, the whole reef dies.
What is causing coral bleaching? Initially it was a mystery, but studies since the mid-1960s indicate that increased sea-water temperatures caused by global warming may be one factor. In some cases, the direct cause of bleaching may be a bacterial infection. Increased water temperatures may lower the resistance of the corals, making them vulnerable to the bacterial invaders.
Water deterioration near major population centers is another implicated factor. Sewage, fertilizer runoff, and high sediment loads in the water kill or stunt the growth of coral polyps over wide areas. Coral reefs are also vulnerable to damage from human activities such as boat anchors, channel clearing, and quarrying for cement manufacture. Once they are gone, taking with them the rich biological communities they support, they cannot be replaced for many hundreds of years.
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