Coral in Virgin Islands National Park

Staghorn coral (Acropora cervicornis) is a fast growing coral species.

NPS Photo/Jamie Irving

A coral is a tiny animal (cnidarian) with a tiny plant (an algae called zooxanthellae) living inside it. The coral takes calcium from seawater and uses it to build a limestone skeleton. The coral provides a home for the zooxanthellae, and the zooxanthellae provide energy for the coral. This is called a symbiotic relationship; two organisms live together for their mutual benefit. Zooxanthellae also give coral its color.

Many corals grow together to form colonies, which are the various and fantastic shapes you see. Lots of colonies growing close together make up the growing structure that we call a coral reef. Reefs also include sponges, algae, and rock, all of which create habitat and homes for fish, mollusks, crustaceans, worms and other marine life.

Coral colonies grow very slowly, sometimes only a few millimeters every year. They require specific conditions to remain healthy. Water that is too warm can cause a phenomenon known as coral bleaching; this is when corals expel their symbiotic zooxanthellae and turn white. Corals cannot survive long without their partners, and in their weakened condition, become more susceptible to disease. A growing percentage of the worlds corals are dying from coral bleaching and disease. Read more here about the crisis of coral disease that is devastating park reefs.

Corals also suffer from more direct human impacts. Stepping on or even touching corals can kill them. Some of the corals in the Virgin Islands have lived for hundreds of years. They have survived hurricanes, anchor damage, coral bleaching, smothering sediment, pollution and disease. Please remember to stand only on sand; give the corals a chance to survive. Learn more here about threats to coral and our oceans.

 

Duration:

13 minutes, 18 seconds

What's happening to the extensive coral reefs underwater off the coast of Virgin Islands National Park? This 13-minute documentary dives into the challenges facing the long-living organisms that are coral reefs. Listen to National Park Service expert Jeff Miller as he describes the importance of coral to the underwater ecosystems and the immense threats of coral bleaching and coral disease. Thanks to Princeton Tonight, Sophia Kim-Brookes, and Noah Mihan for producing this documentary at a crucial time.

How can you protect coral reefs?

 

 

Additional Resources

Coral Bleaching and Disease Deliver “One – Two Punch” to Coral Reefs in the US Virgin Islands (PDF 178 kb)
Coral diseases following massive bleaching in 2005 (Link to report summary and PDF of full report)
Discovering the Secret Gardens in the Mangroves of St. John, U.S. Virgin Islands (Link to investigations about corals living among mangrove prop-roots. Includes a slideshow and links to more articles about St. John.)
Coral Reef ID Cards in English or Spanish. Pictures and descriptions of corals as pdf files.