Australia’s Great Barrier Reef is the largest single structure ever created by living organisms. It consists of 2,900 separate reefs and 900 islands, and stretches 1,400 miles along the Queensland coast in the Coral Sea, and is clearly visible from space. The reef was inscribed as a UNESCO World Heritage Site in 1981. The organisms in question are tiny coral polyps. There are some 400 species of hard and soft corals inhabiting the Barrier Reef. Reefs grow slowly, by means of the deposit of a calcareous remnant of a polyp. Living polyps have zooxanthellae algae living in their tissues in a symbiotic bond whereby the coral supplies materials needed for the algae to photosynthesize, and the algae in turn supply materials needed by the polyps. The algae also gives the corals the colors that we find so enchanting. The reef that mesmerizes us with its myriad colors and shapes, and which supports a fabulous variety of other life forms, is the result of millions of years of such growth. Its survival is believed to be severely threatened by a number of affects, most of which are directly attributable to human activities.