Coral reefs in danger worldwide

Coral pieces
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Coral reef is a type of underwater environment shaped by limestone formations. Reef limestone consists largely of a framework of skeletons from marine animals called corals, says worldbookonline.

Reefs also contain the remains of other limestone-producing organisms, such as algae and shellfish, as well as sand and other particles. A coral reef is a complex, biologically rich ecosystem—that is, a community of living things and their environment. Many of the world's most colorful animals live in coral reefs. Reefs also provide important benefits to people and to the larger environment.

Coral animals produce formations that may resemble branching trees, large domes, small irregular crusts, or tiny organ pipes. They can glow with rich colors, including beautiful shades of green, orange, purple, tan, and yellow.

Coral reefs lie mainly in shallow tropical or subtropical seas. Most reef-forming corals cannot live in water colder than 61 to 68 °F (16 to 20 °C). Reefs require enough sunlight to support photosynthesis in their algae and plants. Photosynthesis is the process in which organisms use energy from sunlight to make food.

Reefs aid people in numerous ways. Many societies depend on reef animals for food. Coral reefs also benefit the economies of some nations by drawing large numbers of tourists. In medicine, doctors use coral limestone to replace parts of human bones, and medical researchers believe chemicals from certain reef organisms may help them discover new medicines.

Despite the benefits coral reefs provide, human activities have led to the destruction of many reef environments. The fishing industry poses numerous threats to reefs. Fishing methods using dynamite, cyanide, or bleach can destroy coral life. Overfishing may upset reef stability by endangering certain reef species. Ships passing too close to reefs can hit and damage them.

The widespread burning of fossil fuels also damages reefs. Such pollution produces large amounts of carbon dioxide in the atmosphere. Excess carbon dioxide contributes to global warming, and thus to a rise in ocean temperatures. High water temperatures can cause corals to bleach and die. Bleaching occurs when corals become stressed and their zooxanthellae die or are expelled from the polyps.

Many other human activities harm coral reefs. Deforestation (cutting down forests) causes soil to wash into the sea and block out sunlight that corals need to survive. Agricultural fertilizers seep into oceans and promote the overgrowth of algae that smother polyps. The development of seaside homes and hotels may cause pollution that poisons corals.