The Great Barrier Reef dominates the upper right portion of this image. The Great Barrier Reef is recognized as one of the most significant ecosystems on the planet and is a United Nations Education, Scientific and Cultural Organization (UNESCO) World Heritage site. It contains a remarkable array of biological diversity, known for its sheer number of species as well as numerous rare, threatened, and sensitive ones. These include over 400 species of coral scattered across over 2,800 separate reefs, creating the largest structure on the planet built by living organisms. The reefs provide shelter to more than 1500 species of fish, 4000 mollusk species and more than 200 bird species. They are also home to dugongs (somewhat similar to manatees) and green turtles, as well as dolphins and other whales. Coral reefs are an example of symbiosis (which means “living together”): they are the product of cooperation between a photosynthetic algae- that provides food to the relationship- as well as a coral, whose chalky, calcium carbonate shell provides shelter. Coral reef systems are very sensitive to disturbance, including global warming, water pollution, tourism, and fishing. When stressed, the symbiotic algae are expelled, causing the coral to turn white â€“ a process known as “bleaching”.