Project: Changing Planet

By: Katie Burdick

Features of Corals

Corals start out as a polyp which then attaches to a rock and builds a limestone skeleton. A coral polyp is a sac that contains a stomach and reproductive tissue. It also contains a mouth surrounded by stinging tentacles. These polyps have a skeleton made of calcium carbonate (limestone) that protects the polyp. The skeleton forms by carbon dioxide and calcium in the water that create the calcium carbonate skeleton (Coral Reef Overview, 2013). The polyp then divides into thousands of clones by budding or fragmentation which grow together to form a colony. Colonies will form reefs. As the skeletons of coral break down over time, some will wash ashore and form beaches. Some will remain in place. New coral will then grow and the reefs will get bigger on top of other dead coral which have settled to the ocean floor.

Coral have a mutualistic symbiotic relationship with zooxanthellae algae. Zooxanthellae algae live inside coral polyp and make food by photosynthesis. The zooxanthellae share their food and oxygen with the coral, and the coral provide shelter and protection. Zooxanthellae also have pigments which give coral their many beautiful colors. So, when the zooxanthellae algae die, the coral loses its color and turns white and often dies as well. This is known as coral bleaching (Stanford, 2012).

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Abiotic Factors

Corals are marine organisms living within a very narrow set of habitat conditions. Changes in these conditions have affected coral reefs around the world.

Corals need lots of high intensity sunlight and water temperatures between 70-90 °F and 22-32°Celsius. These temperatures are found in tropical and subtropical waters.

Reef building coral need shallow waters that are less than 40 meters deep. They also like clear water and gentle wave movements. This is because strong waves like those in storms can break apart coral. Coral need an ocean salinity of 34-37 ppm and a pH of 8.2 (Wijgerde, 2008). At a pH of 7.5, corals start dissolving. One thing that can affect this is how clean the water is. It needs to be free of pollutants and sediments (Ocean World, 2004).

Characteristics of Coral Ecosystems

Coral reefs are located worldwide on both sides of the equator. Coral reefs cover less than 1% of Earth’s surface; yet they are home to at least 25% of all marine species known (Ocean Portal Team, 2013). Some corals are primary producers while others are primary consumers. In most coral reefs, the primary producers are photosynthetic autotrophs such as phytoplankton, seaweed, and zooxanthellae algae in corals. Primary consumers consist of zooplankton, sea urchins, small fish, some crabs, and some corals. Secondary consumers include larger reef fish, lobsters, and sea turtles. The tertiary consumers are reef sharks (Rose, 2008).

Corals are filter feeders and help to keep the water clear. They also provide food and shelter for other organisms. Some of these organisms include crabs and shrimp. In exchange for their protection, they can also help protect the reefs. Coral reefs are home to thousands of organisms and barrier reefs help protect the shorelines. In addition, corals turn carbon dioxide into their limestone skeleton, and thus help control the amount of carbon dioxide in the water (Ocean World, 2004).


Coral reefs support over 4000 species of fish, 800 species of hard coral and could possibly be home to millions of undiscovered species. Coral reefs make great homes and provide protection for more than just fish. Barrier reefs protect our shorelines from erosion, property damage, and loss of human lives during severe storms such as hurricanes. They also protect wetlands, ports and harbors, and the people that live on the shoreline.

Corals even help us beyond protection. They may provide new medicines for cancer, arthritis, viruses, and bacterial infections. Corals are even great for the economy. They provide a food resource as well as commercial fisheries. Tourism is the most grand of all. Diving and fishing tours as well as hotels and restaurants benefit from coral reefs. So, coral reefs even supply jobs for us. Overall, coral reefs provide $30 billion to $375 billion to the economy (NOAA Tutorial, 2012).

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Unfortunately, there are many threats to corals. Human threats include pollution, overfishing, destructive fishing techniques such as bomb fishing, collecting coral for aquariums, and mining coral for building materials. All of these things are damaging the coral, and all of which we do without a second thought or regrets.

The weather can also pay a nasty toll on corals. A hurricane’s powerful waves can break apart corals and scatter them. Then, invasive algae can take over and kill the remaining corals.

Increased sea surface temperatures and decreased sea levels harm corals. If corals are exposed during long periods of low tides, the sun’s ultraviolet radiation will dry out the coral’s exposed tissues and can kill it. This is called a tidal emersion.

An increase of salinity due to changed rain patterns can damage corals and lead to bleaching and death.

Diseases can be caused by biological or non-biological stresses. Biological stresses include bacteria, fungi, and viruses. Non-biological stresses are those like weather. Some of these stresses include an increase in surface temperature, too much ultraviolet radiation, and pollutants. These diseases kill coral’s living tissue and leave behind the bleached white skeleton. After the coral bleaching, the health of the entire colony declines.

Another threat is predation from fish, marine worms, barnacles, crabs, snails, sea stars, and turtles; all of which prey on corals (NOAA Tutorial, 2012).

Reef GIS Data: Cancun, Mexico

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Reef Type

Cancun's reefs types include shelf and fringe reefs.

Coral Bleaching

According to the Reef GIS (2013) maps, Cancun's corals have not been bleached/bleaching is unknown in the area.

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Fortunately, Cancun reefs have not been infected with many diseases to date. The disease known to affect this area is a fungal disease that causes white plague. Other diseases are unknown (Reef GIS, 2013). The map shows that there are no diseases.

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The greatest risks to the Cancun reefs are coastal development and overfishing (Reef GIS, 2013). Coastal development includes hotels, restaurants, sewage, runoff from streets and golf courses, and tourism. Tourism harms the reefs due to too many divers and snorkelers swimming through the reefs. Overfishing harms the reefs due to removing too many fish and creating an imbalance in the food web (trophic levels).

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The Cancun reefs are being monitored for biological and non-biological damage. In that tourism involving diving and snorkeling the reefs provides so much money to the Cancun economy, the local community had to find a way to protect the native reefs. The major achievement regarding protection of the Cancun reefs is the construction of an underwater, artificial reef museum called the Museo Subacuatico de Arte. An underwater city of over 500 art sculptures and statues was built and installed as an artificial reef. Fish and coral have made this area a new home. In addition, tourists are now diving and snorkeling here instead of only along the existing reefs, which allows less stress on the existing coral (Archibold, 2012).

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