What Are Corals?

Types of Coral

Coral species that build reefs are with their calcium carbonate or aragonite skeletons are known as stony corals. Common shapes of coral are: massive, tabular, branching, encrusting, foliaceous, and columnar.

Where Coral is Found

Corals are found in very specific areas with a narrow range of environmental conditions. Reef-building corals are found in shallow, warm water specifically (around 70-85 degrees), between just below the surface and 90 feet deep (although corals can be found up to 100s of feet deep in clear waters). As corals depend on their symbiotic algae for growth, they need to be in areas with high light availability to support photosynthesis. They can only live in seawater and can’t survive near river openings or areas with freshwater runoff. There are many other factors that create an optimal habitat for coral such as a a hard bottom for coral larvae to attach and the presence of prey.

Instructions: The colored circles show where clusters of coral are located. The number shows the count of reefs in that location. Darker circles indicate greater concentration Click a circle to zoom in.

Source: ReefGIS - Reef Locations

Benefits of Coral

Coral Reefs are Worth Billions

Corals provide many important benefits and services to people. The services provided by coral reefs to humans are worth billions of dollars.

Coral Reefs are a Classic Tourist Activity


Snorkeling and scuba diving on reefs are a popular tourist activity. Reefs provide tourists the opportunity to see hundreds of species of marine life all in one place. Estimates suggest tourists spend $11.5 billion globally on coral reef related tourism.

Coral Reefs Break Wave Energy

shoreline protection

Coral reefs protect coastlines because they dissipate wave energy. They can absorb up to 97% of the wave energy. Estimates suggest this is worth $10.7 billion. This is measured by replacement costs (using a man-made structure instead of reefs for protection) or by damages avoided.

Coral Reefs Are Home to Commercially Important Fish

shoreline protection

Fisheries benefit from reefs because they are the natural habitat of many commercially important fish (e.g., groupers, snappers) and invertebrate (e.g., lobsters, conch) species. Fisheries provide fish that are sold to be eaten as well ornamental aquarium fish. Coral reef fisheries are worth $6.8 billion.

Threats to Coral

Over 60% of reefs are threatened by a variety of different factors.

This graph shows the level of threats to coral reefs gobally. These numbers do not account for climate change threats, which threaten all coral reefs.

Climate Change leads to Bleaching

coral bleaching

Corals can only survive in very narrow range of water temperature. The increase in temperature means the water is too hot for them to survive in. The warmer temperature leads to coral bleaching. When the water is too warm, the coral expels the algae they are hosting, losing the algal pigments and causing them to turn white.

The addition of CO2 into the air is absorbed by the ocean making shallow waters more acidic. This increased acidity reduces coral calcification, and can weaken and even dissolve the calcium carbonate skeletons of corals.

Pollution leads to Algae Blooms


When it rains, nutrients from land can get into the water and causes algae blooms. Too much algae in the water column is harmful to coral because it decreases light availability (needed for photosynthesis) and causes algae blooms on reefs that can smother the corals.

Increased sedimentation in coastal waters can also smother corals and reduce light penetration. Chemical pollution from active ingredients in sunscreen on snorkelers and divers in the area can cause damage to corals. The increase in coral disease has been directly attributed to human activity.

Careless Destruction of Coral


Coral mining is when parts of coral are removed for making jewelry or to put in aquariums.

Irresponsible divers and snorkelers stand on the coral and destroy it.

Dredging for the purpose of building an oceanfront restaurant or to bring in cruise ships means destroying any coral in that area.

Grounding boats colliding with coral also leads to their destruction.

Hurricanes are also a source of major physical damage to coral reefs in their path.

Overfishing and Other Destructive Fishing Practices Harm Coral

fishing practices

Destructive fishing practices also take a toll on coral.

Removing herbivorous from the ecosystem either directly or indirectly disrupts the delicate balance which prevents algae from over growing and suffocating the coral.

Cyanide fishing is a practice where fishers use cyanide to stun or kill catch but it also kills coral.

Dynamite fishing is popular in Southeast Asia where it is intended to target the fish, but destroys large amounts of coral at the same time.

Dredging is another common fishing practice that destroys thousand yeah old reefs. A fishing dredge is dragged along the ocean floor and damages coral as it is dragged over it. Corals can also be damaged by traps, fishing line, propellers, and anchors.

Restoration Efforts at UM

Coral gardening is the process of growing corals within underwater coral nurseries to put back into reefs to help restore degraded reef ecosystems. The efforts began at the University of Miami in 2007 when the first UM coral nursery was established in the waters of Biscayne National Park, adjacent to the city of Miami.

Since 2012 UM has planted approximately 600 meters of healthy coral back into the reef. The UM nurseries presently hold more than 2,500 corals to be used for the purposes of restoration.