Coral Reefs

coral with 3 facts about polyps, biodiversity, and 10 national parks with coral

Coral Reefs are amazing habitats; offering vibrant colors and the greatest biodiversity of any marine ecosystem on the planet. Some coral reefs are so large they are even visible from outer space! But coral reefs only occupy less than one tenth of one percent of the ocean floor. The National Park Service has ten parks with coral reefs stretching from the Pacific Ocean to the Atlantic Ocean.


Coral Reef National Parks


Types of Coral in National Parks

There are hundreds of species of coral found in National Park oceans. National park of American Samoa has over 250 species of coral alone! Some common corals you can expect to find in national parks are elkhorn coral, staghorn coral, boulder coral and brain corals.

a triptych of 3 different types of coral
From left: pillar coral, elkhorn coral, and brain coral.

NPS Photos


How are coral reefs formed?

Corals reefs are formed over a process of thousands of years. Each coral reef is made up of colonies of tiny animals called polyps. Each polyp produces calcium carbonate, which makes up their skeleton and protects corals internal bodies; similar to how our skeleton protects our organs. Polyps on their own are colorless, however, each polyp attracts large amounts of algae, called zooxanthellae. These algae live inside the cells of the polyp and gives corals their vibrant colors.

Corals, and the algae inside their polyps, rely on sunlight to produce the energy needed for them to survive and grow. That’s why most coral reefs can be found in shallow, clear water along the coast. Corals crave the marine conditions found in the warm waters of the tropics and sub-tropics.

close up pf pink coral polyps
Polyps help to create corals skeletons.

NOAA Photo/Schmahl


Benefits of Coral Reefs

Coral reefs are vital for a healthy ecosystem.

  • Habitat: They support 25% of all marine animals, from thousands of fish species to sponges to marine mammals.
  • Protection from storms: Coral reefs are also our first line of defense against tropical storms, helping to protect all of our coastal communities.
  • Local Economies: Coral reefs support tourism and recreation, drawing people from all over the world to see their beautiful and diverse ecosystems.

Threats to Coral Reefs

Coral reefs are fragile and sensitive to changes in water quality and temperature. When pollution causes changes in water quality or temperatures exceed their natural tolerances, corals will become stressed and may die if conditions don’t improve.

Stressors to coral reefs are:

  • Rising water temperatures: Corals thrive in relatively warm water, but when water temperatures rise too high, the zooxanthellae are forced to leave. Since these algae give the corals color, when they leave the coral becomes white, appearing bleached.This coral bleaching can cause the reef to die.

  • Ocean acidification: Ocean acidification can affect coral health by making less calcium carbonate available in ocean waters, making it harder for corals to form their skeletons.

  • Predation: Some species can cause damage to coral reefs, like damsel fish and crown of thorn starfish. While they may not be invasive, outbreaks of these species can wreak havoc on reefs.

  • Overfishing: Coral reef ecosystems support an abundance of species, but overfishing can deplete these populations and effect the entire ecosystem.

  • Recreational Impacts: Boat groundings and anchors can harm corals by breaking or scarring them. Sunscreens that include certain chemicals, harm corals reefs and other plants and animals that live in the ocean. Protect yourself and the reef by covering up or wearing mineral-based sunscreens.


NPS Response

The National Park Service studies and monitors coral reefs closely to understand patterns in reef health. Coral reef parks have regulations to prevent damage from boats and anchors. Certain parks also restrict fishing to maintain healthy populations of reef fish. In addition to protecting corals, parks also restore coral reefs by creating underwater nurseries for coral fragments to grow. These fragments can be placed onto reefs and will grow to form new reef structures and provide important habitat for marine life in the coral reef ecosystem.


Inventory & Monitoring


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    Last updated: June 8, 2022


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