• Coral reefs are affected by human activity in a number of ways.coral reef image by Christian Schoettler from Fotolia.com
  
  Coral reefs are among the most diverse and ecologically rich ecosystems on Earth. Made from calcium carbonate secreted by coral polyps, these reefs are living organisms that grow in shallow tropical waters and support intricate food chains of invertebrates and fish species. However, coral reefs are increasingly affected by human activity.
  
  

Over-fishing

• Human over-fishing of certain species can upset the ecological balance of a coral reef, and the fishing practices themselves can cause irreparable damage to the reef's structure. Over-fishing decreases fish populations, having a domino effect on the food-chain, lowering numbers of fish and negatively affecting biodiversity. Furthermore, fish provide certain nutrients that the coral feeds on, helping it maintain itself and grow. Fishing practices such as trawling (dragging nets along the ocean floor) and blast fishing (using dynamite to kill fish) also damage the coral reef.
  
  

Pollution

• Pollution that occurs at sea, such as oil spills, negatively affects coral reefs. However, a less dramatic but more damaging form of pollution is continuing industrial run-off from the land. Fertilizers and pesticides used in farming practices get washed into the sea and cause algae to flourish. This algae depletes oxygen levels in the water. In Australia, run-off from farmland has led to a huge increase in numbers of the crown-of-thorns starfish, and these echinoderms eat coral. Deforestation and industrial development can also cause silt, soil and sediment to wash into the ocean, increasing turbidity in the water and preventing sufficient sunlight from reaching the coral.
  
  

Tourism

• While tourism at coral reefs has proved financially successful for many communities, the tourism trade can have negative effects on the coral upon which it is dependent. These range from sewage from tourist resorts being washed directly into the sea to divers and snorkelers breaking off pieces of coral, which may have been growing for several centuries, as souvenirs.
  
  

Ocean Acidification

• Since the Industrial Revolution, which harnessed the energy of fossil fuels such as coal and oil by burning them and powering machinery, the amount of carbon dioxide (the by-product of said combustion) has been increasing. The oceans have absorbed much of this carbon dioxide but recently research by the National Oceanic and Atmospheric Administration (NOAA) has discovered that it is affecting the pH balance of seawater. By making seawater more acid, the carbon dioxide has reduced the availability of carbonate ions, an essential chemical in the formation of coral.
  
  

Climate Change

• The higher temperatures and increased ultraviolet radiation caused by greenhouse gases depleting the ozone layer has had a significant impact on coral reefs. Corals live in a symbiotic relationship with a certain algae called zooxanthellae, which live inside the corals and assist in providing nutrients and aiding photosynthesis, both of which the coral needs in order to grow. Climate change has hindered the growth of this algae, meaning coral has been less able to reproduce and grow.