Coral Reef

A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. Scientists generally agree on four different coral reef classifications: fringing reefs, barrier reefs, atolls, and patch reefs. Fringing reefs grow near the coastline around islands and continents. They are separated from the shore by narrow, shallow lagoons. Fringing reefs are the most common type of reef. Coral reefs protect coastlines from storms and erosion, provide jobs for local communities, and offer opportunities for recreation. They are also are a source of food and new medicines. Over half a billion people depend on reefs for food, income, and protection. The top threats to coral reefs — global climate change, unsustainable fishing and land-based pollution — are all due to human activities. These threats, combined with others such as tropical storms, disease outbreaks, vessel damage, marine debris and invasive species, exacerbate each other. Worldwide, an estimated one billion people benefit either directly or indirectly from the ecosystem services coral reefs provide. The majority of reef-building corals are found in tropical and subtropical waters. In addition to weather, corals are vulnerable to predation. Fish, marine worms, barnacles, crabs, snails and sea stars all prey on the soft inner tissues of coral polyps. In extreme cases, entire reefs can be devastated if predator populations become too high. Coral reefs are massive structures made of limestone deposited by coral polyps. Often referred to as the “rainforests of the sea,” coral reefs support approximately 25 percent of all known marine species.