Threats
Despite the vitalness of a coral reef to many ecosystems, many coral reefs are in danger. One of the main threats to a coral reef ecosystem is tourism. Many tourists decide to pick at coral reefs in hopes of bringing home a souvenir, not realizing that coral can take thousands of years to get that thick. Also, pollution from pleasure yachts and cruise ships that is not correctly treated accounts for nearly 30% of coral reef loss. The seagrass beds cannot absorb the foreign substance, and as a result, the coral's delicate water conditions are disturbed and the coral may die. Because the coral is home to so many organisms, the amount of commercial fish available decreases as well. Developing hotel resorts close to reefs in order to attract more people causes coral to die from runoff and shorelines to become disfigured. Also, many people believe that since they live far away from a coral reef, that their pollution will not affect the reefs. However, ocean currents can carry pollution anywhere in the world, and runoff from even the farthest buildings can still impact the reefs.
Ocean acidification also plays a big role in why coral reefs are suffering. Since the Industrial Revolution, humans have added more and more CO2 into the atmosphere. The ocean as absorbed 525 billion tons of CO2 from the atmosphere. When CO2 reacts with the seawater, it reduces the carbonate ions in the sea. These carbonate atoms play a huge role in the formation of the coral's calcium carbonate skeleton. This means that the coral can no longer continue to expand as it once had, and the shell begins to disintegrate instead. Another threat caused by rising CO2 levels is that the CO2 creates a blanket over the atmosphere that traps the Sun's heat in the Earth. This causes sea levels to rise. When coral is put under stress by rising temperatures, it pushes out the zooxanthellae that lived in it. Remember that the zooxanthellae gave the coral its color, so this effect is often called "coral bleaching." The relationship between the zooxanthellae and the coral worked because the zooxanthellae produced nutrients for the coral so that the coral did not have to waste energy in making the nutrients itself. Without the zooxanthellae, the bleached coral dies.