Coral reefs are the most diverse habitats on the planet. Reefs occur in less than 1 percent of the ocean, yet are home to nearly one-quarter of all ocean species. These ancient structures make a perfect home for millions of species of fish, crabs, clams, starfish, squid, sponges, lobsters, seahorses, sea turtles, and more. That exceptional diversity has given them the nickname, “rainforests of the sea.”

Shallow corals prefer clear, warm, moving water in subtropical and tropical seas. In the United States, you’ll find shallow coral reefs in:

• American Samoa
• Florida
• Guam
• Hawaii
• Northern Mariana Islands
• Pacific Remote Islands Areas
• Puerto Rico
• U.S. Virgin Islands

While corals may look like plants or rocks, they are in fact animals who take root on the ocean floor. You can think of them as small jellyfish, glued inside a little rock cave. Their small, soft bodies, called polyps, built that cave—a strong skeleton of calcium carbonate—like a clam grows its shell.

Inside the polyp’s body live tiny one-celled algae, called a zooxanthella. This creature contains chlorophyll and, like plants, turns sunlight into sugar. By producing food and oxygen for the polyp, the zooxanthella gets a safe home. That’s why coral reefs need to be in clean, sunlit waters.

Corals have been on earth for at least 400 million years. Coral colonies create the structure of the reef, growing at a typical rate of 0.008 to 0.12 inches per year. Mature coral reefs can be thousands of years old and as big as a small car.

Coral reef ecosystem at Palmyra Atoll National Wildlife Refuge. Credit: U.S. Fish and Wildlife Service.

Benefits of Shallow Coral Reefs

Coral reefs support a multitude of benefits—called ecosystem services—that impact our day-to-day lives. They provide jobs, tourism and recreation opportunities, seafood, wave protection, and more. In total, U.S. reefs provide $1.75 billion in ecosystem services, which include protection from storm surges and destructive waves, employment, and fisheries activity.

Tourism

Our living coral reefs draw 55 million visitors every year to U.S. states, territories, and marine sanctuaries. Sixty percent of Hawaii’s tourist income comes from reef visitors. 

Sustainable Fisheries

Many commercially important fish species, like grouper, snapper, and lobster, depend on coral reefs for food and shelter. The fish that grow and live on coral reefs are a significant food source for billions of people worldwide.

Reef-related fisheries in the United States are valued at more than $100 million. Half of all U.S. fisheries depend on healthy coral reefs. In Florida, where many fisheries depend on reef-raised species, an estimated $28.7 billion in sales come from commercial and recreational fishing industries.

Employment

From hotel rooms to dive trips, from clothing and gear to sport fishing, coral reefs support jobs for American workers. In southeast Florida alone, coral reefs generate $324 million in annual local sales and support more than 70,000 jobs. Hawaii attributes $304 million directly to reef tourism and recreation.

Storm Barriers

Reefs provide natural breakwaters, which buffer shorelines from waves and storms. Their rough surfaces and complex structures dissipate the force of incoming waves. This helps prevent flooding, erosion, property damage, and loss of life. 

Medical Discoveries

Coral ecosystems are an important source of new medicines. For example, anti-cancer drugs are derived from certain marine algae, the mucus of cone snails yields a potent painkiller, and a deep-sea sponge shows promise in the treatment of pancreatic cancer.

Challenges for Shallow Corals

Despite their great economic and recreational value, coral reefs are threatened throughout the world. For example, elkhorn and staghorn coral populations in the Caribbean have declined by more than 90 percent in the last 25 years. In Florida, an ongoing multi-year outbreak of stony coral tissue loss disease is impacting the continental United States' only living barrier reef.

Threats to coral reefs include:

• Pollution from land runoff
• Oil and chemical spills
• Marine debris, trash, and plastic
• Sedimentation
• Nutrient pollution from fertilizers and sewage
• Bottom-trawling and overfishing
• Invasive species
• Disease
• Rising water temperature
• Ocean acidification
• Vessel groundings
• Unsafe diving and boating habits

Once reefs are damaged, they become less productive. Fewer reef residents means less food for young fish, and that leads to declining fisheries. With the loss of colorful marine life, snorkeling and scuba-diving tourists stay away and the local economy suffers.

Climate Change

Climate change is the greatest global threat to coral reef ecosystems. As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent. Other effects of climate change—such as sea level rise, more frequent and intense tropical storms, and changing ocean circulation patterns—dramatically alter how coral reef ecosystems function.

Ocean Acidification

When carbon dioxide is absorbed into the ocean from the atmosphere, it causes seawater to become more acidic. This dissolves the shells of ocean creatures like corals, and decreases the rate at which they’re able to rebuild. The reef grows more fragile and less able to protect its residents. 

Coral Bleaching

Prolonged high water temperatures can cause coral polyps to expel their symbiotic partners, the tiny algae that help them produce food. The coral colony will turn white because the algae provide the color to most hard corals. The polyps cannot live long without their zooxanthellae partners, placing the whole reef at risk.

Land-Based Sources of Pollution

Land-based sources of pollution like runoff, sediment, sewage, and nutrients threaten coral reefs. They can overwhelm corals, lowering their ability to filter pollutants. Smothering algae, disease, and low oxygen degrade and damage the reef.

Invasive Species

A healthy habitat is a balanced, interdependent system that can be toppled by non-native species. When new species with no local predators are introduced, they can take over, altering reef habitats by consuming light, oxygen, food, and other resources. When the reef is weakened or corals die, native species will decline and disappear. 

Physical Impacts

Located close to the ocean’s surface, coral reefs are at risk for physical impacts caused by ship groundings, anchor damage, and storms. This can result in significant local losses of corals that are hundreds of years old.

What We Do

We Protect Coral Reefs

The best way to conserve coral reefs and reduce future habitat loss is to know everything we can about them. We address coral conservation priorities by locating, surveying, and monitoring America’s coral reefs in the Caribbean (Florida, Puerto Rico, U.S. Virgin Island) and the Pacific (American Samoa, Guam, Hawaii, Northern Marianas Islands).

As part of the NOAA Coral Reef Conservation Program, our Coral Reef Information System organizes data from all NOAA and partner actions, including:

• Reef mapping
• Monitoring and assessment
• Biological and socioeconomic research and modeling
• Outreach and education
• Management and stewardship

We’ve studied how coral reefs enhance local economies, water quality, and fishery productivity. Monitoring reef health means we can respond quickly to mitigate invasive species and disease, as well as land-based sources of pollution, vessel groundings, and oil spills.

We Restore Coral Reefs

The Office of Habitat Conservation’s NOAA Restoration Center provides funding and technical assistance to habitat restoration projects across the country, including efforts to restore coral reefs. We work with the NOAA Coral Reef Conservation Program, the Damage, Assessment, Remediation, and Restoration Program, and other NOAA offices to help threatened shallow coral species recover.

For example, NOAA and partners are working in the Florida Keys to implement Mission: Iconic Reefs, a first-of-its-kind approach to restoring corals at seven ecologically and culturally significant reef sites in Florida Keys National Marine Sanctuary. By the end of this effort, coral cover across the seven sites will be restored from 2 percent to an average of 25 percent.

We participate in a diverse set of coral-related restoration activities across the Caribbean and Florida, as well as in the Pacific. Our work includes:

• Facilitating, leading, funding, and implementing efforts to grow corals in protected conditions. NOAA and partners collect broken corals and grow them in dense coral nurseries. They are then reattached to reefs piece by piece with cement, zip ties, and nails. 
• Combating invasive species, such as algae, that disturb the balance of life on reefs. To further prevent reefs from being smothered, we work to reduce runoff of sediment and other pollutants, which can feed algae growth, from nearby land.
• Establishing a contract-based emergency response system to address ship groundings and other physical impacts to corals. This system has responded to hundreds of incidents, saving tens of thousands of corals.

We Partner to Support Coral Reef Habitat

To address the complex nature of threats that face shallow and deep sea coral, we work to protect these valuable habitats through the NOAA Coral Reef Conservation Program and with partners.

Restoration funding provided by the program enables state and local organizations to conduct projects of value to their communities. For every million dollars in grants we award, 15 or more jobs are created in addition to the resource recovery value.

What You Can Do

• Learn more about coral reefs. Share your new knowledge!
• Volunteer. Get involved in community coral reef restoration, monitoring programs, aquariums, and beach cleanups. For example, the Southeast Florida Action Network uses community volunteers to help report coral disease.
• Purchase wisely. Buy ethically raised and legally collected aquarium fish and corals. Don't buy live corals, jewelry, or decorative items without knowing the source and sustainability of the coral.
• Practice good coral reef etiquette. Remember, you are visiting the animals’ home. Avoid touching or taking coral if you dive on a reef. Keep hands and fins off the reef, and avoid stirring up the bottom. These sediments can smother corals. 
• Boat safely. If you go boating near a coral reef, don’t anchor on the reef. Use mooring buoy systems when available, and make sure sewage from your boat or RV is correctly handled. 
• Use mineral-based sunblock. Avoid chemical-based sunscreens, which can be extremely harmful to marine life. 
• Eat sustainable seafood. Visit Fishwatch.gov to find good choices.
• Avoid chemically-enhanced pesticides and fertilizers. Although you may live thousands of miles from a reef ecosystem, these products can flow downstream.
• Conserve water. The less water you use, the less runoff and wastewater eventually finds its way back into our oceans.
• Reduce, reuse, recycle. Don’t trash the sea. Report dumping or other illegal activities.
• Shrink your carbon footprint. Reduce your greenhouse gas emissions, which contribute to warming oceans that threaten coral reefs.

More Information

• Restoring Coral Reefs
• NOAA Coral Reef Conservation Program
• National Coral Reef Monitoring Program
• Protecting Coral Reefs
• Corals: The Bottom Line (video)