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Degradation of Coral Reefs

Coral reefs are some the oldest, most complex ecosystems of plants and animals on Earth. At about 200-400 million years old, they span 231,660 square miles worldwide. Coral reefs are made up of a mostly calcareous skeleton formed by marine invertebrate organisms known as cnidarians. Corals are found in most oceans around the world but are most abundant and diverse in relatively shallow tropical waters, which have constant temperatures. Coral reefs are so diverse in species that they are often called the “rainforest of the sea.” These highly productive marine ecosystems may contain over 3,000 species of fish, shellfish, and other invertebrates. About 33% of all the fish worldwide depend on coral reefs.

Unfortunately, due to the actions of humans, coral reefs are being degraded and destroyed. In 2015, 100 out of 109 countries with coral reef formations have reported a loss of coral since 2000. 93 of those countries reported “significant reef damage or loss.” Because coral and their plant symbionts thrive within a very narrow range of physical and chemical conditions, any change in conditions is disastrous. Recent studies show that coral reefs around the world are increasingly stressed or on the verge of collapse due to rising marine acidity levels, rising sea temperatures, and overfishing.

Silt washes into the seas due to erosion by clearing cutting trees inland. Silt can cloud the sea or smother the coral, which prevents photosynthesis. Oil and other toxic chemicals that spill into the marine system kill coral and other organisms in the environment. Mining reefs for an aquarium and rare marine species are also hazards: those who sell coral illegally and spray the coral heads with poisonous solutions to stun the fishes and cause them to abandon the reef. This efficient method leaves the coral enveloped in a cloud of poison, which kills the entire section of the reef.

Due to the warming of the oceans, the corals are turning white (bleaching). Bleaching leaves the corals susceptible to diseases. After long-term exposure to high temperatures, the coral eventually dies. As much as 50% of coral in the Virgin Islands die due to bleaching.

Tourism and recreation also cause degradation of the coral reefs. Coral is being destroyed by the propellers of recreational boats, and divers who unintentionally step on coral heads, breaking them to pieces. Due to this degradation, many sections of coral reefs have been set aside for protection. There are 300 protected areas in 65 countries. Despite all the effort, increasing pollution, coupled with the actions of man, these complex communities of marine organisms are being destroyed.

Edited by: Daryn Dever, Karen Yung, and Shreya Singireddy

“Aquarium trade.” Environmental Encyclopedia, edited by Deirdre S. Blanchfield, Gale, 2011. Science in Context,

“Coral bleaching.” Environmental Encyclopedia, edited by Deirdre S. Blanchfield, Gale, 2011. Science in Context,

“Coral reef.” Environmental Encyclopedia, edited by Deirdre S. Blanchfield, Gale, 2011. Science in Context,