The Coral Reef Ecosystem

A coral reef ecosystem consists of marine structures made of calcium carbonate secreted by living organisms. Most coral reefs are built by stony corals. Stony corals consist of hundreds of thousands of small animals known as polyps that form colonies on the reefs. The coral reef ecosystem contains a wide variety of marine species greater than in any other marine habitat, making it one of the most diverse on Earth. The marine biodiversity in a coral reef is greater than in any other marine ecosystem.

Habitat of 1/4 of marine species

Coral reefs are some of the most diverse ecosystems in the world. Although, they occupy less than one percent of the oceans around the world, they are the habitat of one quarter of all marine species, some of which include, fish, mollusks, crustaceans, sponges, tunicates, cnidarians, and echinoderms. It is estimated that the coral reef ecosystem supports more than 800 hard coral species and more than 4,000 species of fish. This accounts to about 25% of the world’s fish biodiversity. It is thought that millions of undiscovered species may be living in coral reefs.

Most coral reefs form at 30° north or sout of the equator

Corals thrive in ocean water temperatures ranging from 23 to 29 ºC, although some can tolerate other temperatures. Most corals exist in the shallow-water reefs at 30° North or South of the equator. These type of corals require sunny, shallow, clear and nutrient-free water to allow their symbiont algae to use the sunlight for the process of photosynthesis. The need for sunlight restricts coral reefs to the euphotic zone 100 meters in depth. Deep-water coral reef formations are known to exist at higher latitudes and greater depths, although studies about their formation need further research.

Coral reef formations

Coral reef formations begin to form when diminute coral larvae attach to hard substrates along the edges of islands and continental land. Depending on where in the ocean they form, coral reefs make take one out of three forms. Fringing reefs, barrier reefs and atolls. Barrier reefs usually grow near the coastline around islands and continental land. Barrier reefs grow along the coastline but are divided by a lagoon; at the shallowest point, the coral reef can reach the surface forming a natural barrier to navigation. Atolls are rings of coral surrounding a lagoon. They usually form when an island surrounded by fringing reef sinks down into the ocean.

Coral triangle

Most coral reefs are found in tropical and subtropical waters located at 30° North or South of the Earth’s equator. The coral triangle, comprising the Indo-Pacific region contains the greater coral reef biodiversity in the world and accounts to more than one quarter of the world’s reefs. Coral reefs may grow about half of one inch every year; however, if a coral reef remains undisturbed by man, it can grow huge, such is the case of The Great Barrier Reef off the coast of Australia. This reef measures 150 km (93 miles) across by 2000 km (1,242 miles) long.

Coral reefs are among one of the most biological diverse and economically valuable ecosystems in the world. They provide habitat to more marine species than any other known marine ecosystem. The coral reef ecosystem provides habitat for an approximate number of 4,000 fish species, 800 species of coral, among other marine plants. According to, coral reefs are among the most biodiverse ecosystems in the world and they provide valuable services, including recreation, fishing, tourism, protection against storms in the coastline. Coral reef animals and plants are important sources of new medicines being developed to treat a variety of diseases, inlcuding cancer, heart disease, arthritis, viruses and bacterial infections, among other diseases.