"The corals and algae have a mutualistic relationship," states the National Oceanic and Atmospheric Administration. Zooxanthellae, also known as photosynthetic algae, are present in reef-building corals. Zooxanthellae are vital in providing a coral reef with proper nutrition, in an environment filled with poor nutrition. Clade D zooxanthellae are especially beneficial in protecting the reef from the harsh environmental factors that destroy it. Algae give coral oxygen, and assist it in removing its waste. Coral provides algae an environment conducive to photosynthesis.
According to the Cooperative Research Centre for the Great Barrier Reef World Heritage Area, red calcareous coralline algae cement coral together and build the reef's structure. Calcareous algae produce calcium carbonate and organic matter in tropical and subtropical coral reefs. The algae significantly contribute to maintaining a healthy reef -- making the reef stronger and protecting it from erosion.
Natural disturbances, coral mining, coastal development, overfishing, storms and pollution cause algae blooms, which smother and destroy coral reefs. Algae give coral its vibrant color. When algae die or leave the reef, the coral reef is destroyed. As a result, the coral reef turns white in appearance, which is known as coral bleaching. Harmful algae kill the coral reef, because it blocks sunlight, which is necessary for the reef's survival. Fish eat algae and control algae growth. Overfishing causes excessive algal growth, which kills hard coral colonies.
Trash; fertilizers; sewage, which contains high amounts of nitrogen; sedimentation; oil, gas and pesticides pollute water and contaminate algae. This in turn destroys the tropical coral reefs that have taken years to grow. Global warming causes the earth's temperature to become hotter -- extremely harmful to algae. Global warming can kill algae and as a result the coral reefs die.
