Coral reefs are one of the most complex and colorful tropical ecosystems, rivaling rain forests in their richness of life. Coral reef organisms build massive & intricate physical structures that are home to some of the most fascinating plants and animals in the world. Their extraordinary beauty captivates visitors and their productivity provides a wealth of resources for local communities and the world.
Coral reefs are massive structures made of limestone that is deposited by living things. Although thousands of species inhabit coral reefs, only a fraction produce the limestone that builds the reef. The most important reef building organisms are corals.
Coral reefs support over twenty-five percent of all known marine species. As one of the most complex ecosystems on the planet, coral reefs are home to over 4,000 different species of fish, 700 species of coral and thousands of other plants and animals.
A good way to imagine a coral reef is to think of it as a bustling city or community, with the buildings made of coral, and thousands of inhabitants coming and going, carrying out their business. In this sense, a coral reef is like a metropolis under the sea.
Although coral is often mistaken for a rock or a plant, it is actually composed of tiny, fragile animals called coral polyps. When we say “coral” we are actually referring to these animals and the skeletons they leave behind after they die.
Although there are hundreds of different species of corals, they are generally classified as either “hard coral” or “soft coral”.
Hard corals grow in colonies and are the architects of coral reefs. They include such species as brain coral and elkhorn coral. Their skeletons are made out of calcium carbonate (also known as limestone) which is hard and eventually becomes rock. Hard corals are hermatypes or reef-building corals and need tiny algae called zooxanthellae (pronounced zo-zan-THEL-ee) to survive. Generally, when we talk about “coral” we are referring to hard corals.

Soft corals such as sea fingers and sea whips, are soft and bendable and often resemble plants or trees. These corals do not have stony skeletons, but instead grow wood-like cores for support and fleshy rinds for protection. They are referred to as ahermatypes or non-reef building corals and they do not always have zooxanthellae. Soft corals are found in both tropical seas and in cool, dark regions.
Coral reefs are found in over 100 countries. Most reefs are located between the tropics of Cancer and Capricorn, in places such as the Pacific Ocean, the Indian Ocean, the Caribbean, the Red Sea and the Arabian Gulf. Corals are also found farther from the equator in places where warm currents flow out of the tropics, such as Florida and southern Japan. Worldwide, coral reefs cover an estimated 284,300 square kilometers (110,000 square miles).
Coral reefs grow best in waters with a temperature of between 21 and 29 degrees Celsius (70 and 85 degrees Fahrenheit). It is possible for soft corals to grow in hotter and colder places, but growth rates under these conditions are very slow. Corals prefer clear and shallow waters, where lots of sunlight filters through to their symbiotic algae. It is possible to find corals at depths of up to 91 meters (300 feet), but reef-building corals grow poorly below 18-27 meters (60 to 90 feet). Corals also grow poorly near river openings or coastal areas with excessive run-off, because corals need salt water to survive.

The Mesoamerican Barrier Reef System (MBRS) is a large complex Marine ecosystem, with high biodiversity which extends over 4 countries, Mexico, Belize, Guatemala and Honduras. It is over 1000km long and is the second largest barrier reef in the world. It extends from Isla Contoy off the North of the Yucatan Peninsular to the Bay Islands of Honduras, with over 350km along the coast of Quintana Roo

The MBRS contributes to the stabilization and protection of coastal landscapes and habitats, maintenance of coastal water quality, and serves as breeding and feeding grounds for marine mammals, reptiles, fish, and invertebrates plus associated prey groups. Many of these taxa are of commercial importance. It also provides valuable economic resources through activities related to fishing, coastal development, and tourism, thus supplying employment and revenue to local populations and states.

Unfortunately the natural ecosystems comprising the MBRS are under threat by a number of increasing pressures which include coastal and tourism development, pollution from point and non point sources, coastal aquaculture, shrimp farming and domestic waste on the reef, over fishing, increased tourism activities and other non sustainable uses. In addition, it is subject to periodic natural phenomena which include episodes of warm water temperature, flooding (which increases sedimentation) bleaching, outbreaks of disease, storms and hurricanes. These effects are occurring all over the wider Caribbean region resulting in a negative impact upon the regions coastal Marine ecosystems 
Why conserve coral reefs?
The ecological and economic qualities of coral reefs are conventionally used to quantify their value but increasingly other factors, such as their intrinsic and cultural value, are being recognised.

Ecological Biodiversity
- Reef systems are home to an estimated one million species.
- There are more species per unit area of coral reef than in any other ecosystem.
- The level of specialisation has been pushed to extremes, adapting to specific diets, cryptic habitats and highly evolved defence mechanisms.
- It is estimated that less than 10% of the Earth's reef organisms are known to science.

Coastal protection
- Reef systems provide a natural buffer against waves, storm surge and floods for more than 100,000km of coastline.
- During storms they are a key factor in preventing the loss of life, property and erosion.
- They contribute to the formation of sandy beaches and sheltered harbours.

Economic Medicines
- Recent research has linked compounds found in coral reef species with treatments for heart disease, cancer, HIV, arthritis, human bacterial infections, viruses, and other diseases.
- Increasing research in this field suggests that coral reefs will increasingly become an important resource for medical treatments, nutritional supplements, pesticides, cosmetics, and other commercial products.
- Cone snails are thought to contain more chemicals useful to medical research than any other group of organisms on the planet.

Tourism
- The billions of dollars spent each year on diving tours, recreational fishing trips, hotels, restaurants, and other businesses based near reef ecosystems create livelihoods for an enormous number of people worldwide.

Fisheries
- Coral reefs provide a wide range of harvestable species, including fish, molluscs and crustaceans.
- For generations, many developing coastal communities depended on them as a primary food source.
- With the increasing populations of many of the developing countries within which coral reefs commonly occur, coastal communities must manage their resources in a sustainable manner to ensure they can continue to be harvested in the future.
- Reef ecosystems are vital in providing nutrients and breeding grounds for many oceanic commercial species, as well as the reef dependent species which we commonly think of.

Building
- Coral reefs are a source of raw materials in many parts of the world.
- Extraction practices can have immediate consequences on the reef and nearby beaches, such as high levels of siltation resulting in coral reef mortality and coastal erosion. This leads to destabilization of the coast and collapse of buildings.

Nutritional
- Coral reefs provide the main source of animal protein for 1 billion people in Asia alone.

Aquarium trade
- It is estimated that 1.5 - 2 million people around the world keep marine aquaria.
- If managed properly, aquarium species could become a high value source of income in coastal zones with limited resources.
- The problem with this form of exploitation is the destructive techniques used, and the lack of quantitative data to measure its environmental impact.
- Huge numbers of vulnerable reef organisms are removed from the reefs every year to supply the burgeoning aquarium trade, upsetting the ecological balance of the systems.

Many thanks to Daniel Ponce-Taylor, marine biologist, for contributing his time and expertise to this page

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