National Geographic : 2011 May
• Culturally, the reef has been a rich part of the landscape for Aboriginal and Torres Strait Islander peoples, who have canoed it and shed it and shared myths about its creatures for gen- erations. But historians aren't sure how deep their knowledge went of the reef 's geology and animal life. A few decades a er Cook's run-in with the behemoth beneath the sea, English cartographer Matthew Flinders---who also had a mishap or two while "threading the needle" among the reefs---gave the entity its name, inspired by its size. All told, if the reef 's main chunks were plucked from the sea and laid out to dry, the rock could cover all of New Jersey, with coral to spare. EXPANSION AND EROSION is mam- moth reef owes its existence to organisms typi- cally no bigger than a grain of rice. Coral polyps, the reef 's building blocks, are tiny colonial ani- mals that house symbiotic algae in their cells. As those algae photosynthesize---using light to create energy---each polyp is fueled to secrete a "house" of calcium carbonate, or limestone. As one house tops another, the colony expands like a city; other marine life quickly grabs on and spreads, helping cement all the pieces together. O Australia's eastern edge, conditions are ripe for this building of stone walls. Corals grow best in shallow, clear, turbulent water with lots of light to support photosynthesis. Millions of polyp generations later, the reef stands not as a singular thing but as a jumble whose shapes, sizes, and life-forms are determined by where in the ocean they lie---how close to shore, for example---and what forces work on them, such as heavy waves. Go far enough from the coast, where the light is low and the waters are deeper, and there's no reef at all. "In the Great Barrier Reef, corals set the pat- terns of life from end to end," says Charlie Ve- ron, coral expert and a longtime chief scientist for the Australian Institute of Marine Science. With over 400 species in the region, "they struc- ture the entire environment; they're the habitat for everything else here." e perfect tempera- ture, clarity, and currents enable plate corals, for example, to increase in diameter up to a foot IF THE REEF'S MAIN CHUNKS WERE PLUCKED FROM THE SEA AND LAID OUT TO DRY, THE ROCK COULD COVER ALL OF NEW JERSEY, WITH CORAL TO SPARE. Cardinal sh zip by a hawksbill turtle as it rests among feathery invertebrates called hydroids. Illegally harvested for their shells, hawksbills are declining globally. Some 3,000 nest along the northern Barrier Reef. ERETMOCHELYS IMBRICATA TURTLE ; APOGON LEPTOFASCIATUS FISH ; LYTOCARPUS SP. HYDROID David Doubilet divided his time between the Great Barrier Reef 's remote north and its touristed south and central areas. Jennifer S. Holland is a sta writer.