Shallow Coral Reef Habitat
Coral reefs are underwater structures built by tiny sea animals. Hard corals, which have a stone-like skeleton, grow into reefs on the edges of tropical islands and continents. Their beautiful shapes and colors are a magnet for divers, but they also provide an excellent home for thousands of marine creatures, including fish we love to eat.
Corals create a rich habitat for sea life of all kinds.
Rainforests of the Sea
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.”
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 polyps’ body live tiny one-celled algae, called a “zooxanthellae.” This creature contains chlorophyll and, like plants, turns sunlight into sugar. By producing food and oxygen for the polyp, the zooxanthellae 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. Mature coral reefs can be thousands of years old and as big as a small car. Growing at a typical rate of 0.2 to 8 mm (0.008 - 0.12 inches) per year, coral colonies create the structure of the reef.
Shallow corals prefer clear, warm, moving water in subtropical and tropical seas. In the United States, you’ll find shallow coral reefs in:
Northern Mariana Islands
Pacific Remote Islands Areas.
U.S. Virgin Islands.
Coral reef ecosystem at Palmyra Atoll National Wildlife Refuge.
The Value of Shallow Coral Reefs
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.
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 more than one billion people worldwide. Reefs provide shelter to hundreds of species, including newly hatched commercial fish. Reef-related fisheries are valued at more than $200 million, and the fish that grow and live on coral reefs are a significant food source for billions of people worldwide. 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.
Coral reefs around the world feed a billion people and contribute a staggering $172 billion dollars a year to the global economy.
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.
Reefs provide natural breakwaters, which buffer shorelines from waves and storms. Their rough surfaces and complex structures dissipate the force of incoming waves, helping prevent flooding, erosion, property damage, and loss of life. In total, U.S. reefs provide $1.75 billion in ecosystem services, which includes protection from storm surges and destructive waves, employment, and fisheries activity.
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, our coral reefs are gravely threatened by environmental damage. Elkhorn and staghorn coral populations in the Caribbean have declined by more than 90 percent in the last 25 years. Once reefs are damaged, they become a 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.
Seawater is becoming more acidic, which dissolves the shells of ocean creatures like corals. The reef grows more fragile and less able to protect its residents. Other effects from changing water chemistry are yet unknown.
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 algaes, disease, and low oxygen degrade and damage the reef.
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.
Located close to the surface, corals 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.
Threats to Coral Reefs
Despite the importance of coral reefs, these habitats are threatened throughout the world. Threats include:
Pollution from land runoff.
Oil and chemical spills.
Marine debris, trash, and plastic.
Nutrient pollution from fertilizers and sewage.
Bottom-trawling and overfishing.
Rising water temperature.
Unsafe diving and boating habits.
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:
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
NOAA’s Restoration Center works with the Coral Reef Conservation Program and the Damage, Assessment, Remediation, and Restoration Program to help threatened shallow coral species recover.
We facilitate, lead, fund, and implement 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. More than 20 coral nurseries are now active throughout the Caribbean. They provide more than 40,000 healthy corals annually for reef restoration throughout the region.
We also combat the invasive species that disturb the balance of life on reefs. In Hawaii’s Kaneohe Bay, reefs were overgrown with algae, blocking life-giving sunlight and smothering the corals. After careful study, we used an underwater vacuum nicknamed the “Super Sucker” to suck invasive algae off the reef and released a native algae-eating sea urchin that chowed down on the invasive algae, restoring life and color to the reef. To further prevent reefs from being smothered, we work to reduce runoff of sediment and other pollutants from nearby land, which can feed algae growth.
We have established 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 with State and Local Organizations
To address the complex nature of the threats that face shallow and deep sea coral, we work to protect these valuable habitats through our Coral Reef Conservation Program.
Restoration funding provided by the program inspires 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.
Where We’ve Made a Difference
NOAA pioneered a method using hungry native sea urchins and a form of sea-vacuuming to free an urban reef from algal overgrowth.
In Puerto Rico
After Hurricane Matthew, we rescued nearly 7,000 coral fragments that were damaged by the storm. We worked with partners to transplant 5,000 fragments and stabilize another 2,000.
We grew staghorn and elkhorn coral to restore reefs damaged by bleaching, hurricanes, groundings and disease. The project has produced more than 30,000 branching corals, far exceeding the initial goal of 12,000 coral colonies. These survivors recovered from bleaching, which suggests they are more resilient to the stresses that cause it.
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. Not near the coast? Join your local save the river, bay, or lake’s conservation organization and help clean the waterways. All waters drain to the ocean.
Purchase wisely. Buy ethically raised and legally collected aquarium fish and corals.
Donate or become a member. Join your local aquarium or environmental club.
Visit a reef. Support coastal communities.
Practice good coral reef etiquette. Remember, you are visiting the animals’ home. Treat them and their home with respect.
Eat sustainable seafood. Visit Fishwatch.gov to find good choices.
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.
Buy coral products: Don't buy live corals, jewelry, or decorative items without knowing the source and sustainability of the coral.
Touch or take 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.
Anchor on the reef. If you go boating near a coral reef, use mooring buoy systems when available. Make sure that sewage from your boat or RV is correctly handled.
Use chemical-based sunscreens. They can be extremely harmful to marine life. Use mineral-based sunblock instead.
- Use chemically-enhanced pesticides and fertilizers. Although you may live thousands of miles from a reef ecosystem, these products can flow downstream.
Corals: The Bottom Line (video)
Essential to our Economy (video)