Coral Reefs: A Closer Look

Coral reefs are stony structures created by millions of coral polyps – tiny animals with a mouth, stomach, tentacles and thousands of stinging cells, called nematocysts (ne-MAH-toe-sists). Coral polyps look like a miniature upside-down jellyfish, which along with the sea anemone, is a coral polyp's closest relative. Coral polyps excrete a substance called calcium carbonate that forms the hard structures we think of as a coral reef. Coral reefs are like thousand-year-old condominiums for coral polyps.

Since coral polyps are animals, they need to get food. Polyps can do this in two ways. First, they use their tentacles to grab microscopic prey (like plankton). They sting the prey with their nematocysts, which injects venom into the prey to immobilize it. The polyp then brings the prey into its mouth where it is digested in its stomach.

The second way a coral polyp gets food is the most important way. Inside of every cell in the polyp there lives symbiotic algae called zooxanthellae (zō-zan-THEL-ee). Since zooxanthellae are a type of plant, they make their own food through photosynthesis. One of the products of photosynthesis is sugar, which the coral polyp uses as its main source of nutrition. This symbiotic relationship is one of nature’s amazing ways of ensuring the long-term existence of coral reefs.

Coral reefs have been around for millions of years and include some of the largest naturally-made structures on earth. Coral reefs do not appear overnight, in fact corals are some of the slowest growing organisms in the world. Many of the reef-building coral species grow no more than 2.5 cm (1 inch) per year. Because of this slow growth rate, damage to coral reefs is tragic thing. One fin, one hand, or one anchor can kill a thousand-year-old coral head, which will take another thousand years to rebuild.

Reefs in the U.S. Virgin Islands: Our Living Treasures

There are over 40 species of coral in the Caribbean ranging in size, shape and color. Some of the most conspicuous corals on our reefs are also the most important reef-building corals; elkhorn and staghorn corals. Like these, many coral names describe the shape of the coral structure such as pillar, star, finger and brain coral. There are also different reef forms in the USVI including fringing reefs, patch reefs and barrier reefs [see St. Croix Habitats page].

The reefs of the U.S. Virgin Islands are home to a great diversity of organisms including over 400 species of colorful fish, 3 species of magnificent sea turtles, fascinating marine invertebrates like sea stars, urchins and lobsters and sea plants to provide photosynthetic production to the life that these reefs support. It is said that one million different organisms are found on coral reefs, with only about 10% of them identified so far. This cornucopia of life creates a spectacular underwater treasure worthy of exploration, understanding and conservation.

Benefits of Coral Reefs: Deeper than Beauty

In the United States Virgin Islands, coral reefs form the basis of our economy and culture. These intricate and living ecosystems protect our shorelines, bring in tourism, support local fishermen and play an integral role in the daily lives of all who live here. In 2003, 2.3 million tourists came to the USVI and spent $1.2 billion dollars. Many visited our coral reefs to scuba dive, snorkel, and fish. Coral reefs provide food and shelter to 25% of the world’s marine organisms and are the preferred habitat to over ¼ of all marine species. All of these reef organisms play a part, either in directly building the reef, or by being part of the food web and life cycle of the reef. A healthy coral reef can protect the shore and coastal communities from large waves caused by storms, prevent coastlines from erosion, and provide sand for beaches. Because coral reefs harbor thousands of species we can learn a great deal about our living world by studying them. More importantly, scientists are beginning to derive new medicines from reef species for a wide range of illnesses, including heart disease and HIV.  Already, due to their resemblance and chemical make-up, certain coral skeletons are being used in reconstructive surgery as bone substitutes.

The Future of Our Reefs: Is It Too Late?

Coral reefs face threats both natural and human made. Storms and hurricanes can cause severe damage. Diseases, like coral bleaching, can lead to widespread coral die off.

Scientists recently discovered that African dust, carried over to the Caribbean by wind currents, is further causing disease outbreaks. Yet human activity remains the largest threat to coral reefs here in the USVI and worldwide.  Coastal development and runoff smothers reefs and blocks them from the light they need.  Causing further harm to reefs is pollution that makes its way from land to sea.  Global climate change may pose the greatest threat to reefs worldwide, altering seawater temperatures and increasing the severity of storms and hurricanes which can be fatal.

The good news is there is much we can do to help coral reefs. Remember that corals are living animals and touching will cause them harm.  Learn as much as you can about coral reefs and share your knowledge with others. The more people know about this amazing ecosystem the more likely protection will occur.  Global climate change poses extreme threat to coral reefs worldwide so please remember to conserve energy.  Support groups at home and abroad working to protect coral reefs.  Learn more about what you can do to help at http://www.coralreef.noaa.gov/outreach/thingsyoucando.html