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Ancient Lobe Coral
Photograph by Brian J. Skerry, National Geographic
Marine ecologist Enric Sala (foreground) examines an enormous lobe coral on Kingman Reef in the South Pacific’s remote Line Islands. This coral is 500 years old, but the species was unknown to science before Sala’s discovery. Such finds aren’t shocking at Kingman, which is one of the world’s most pristine reef ecosystems. The site shows scientists how much has been lost at reefs found closer to human habitation.
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Pygmy Sea Horse and Coral
Photograph by Paul Sutherland, National Geographic
Coral polyps are transparent, not colorful, yet coral reefs abound with vibrant hues. The color comes from algae, which lends reefs the tropical colors most associate with these lush landscapes. Reef species like this pygmy sea horse adapt to their colorful environment by donning their own vivid hues. Both hunter and hunted use color for camouflage on the reef.
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Golden Sweeper Fish on Coral Reef
Photograph by David Doubilet, National Geographic
Coral reefs are some of the world’s most biologically diverse ecosystems, often called the "rain forests of the sea." Though they spread over less than one percent of the seafloor coral reefs support a staggering one-fourth of all marine species.
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Broccoli Coral
Photograph by David Doubilet, National Geographic
These yellow "stalks" of broccoli coral are just one of a surprising array of coral shapes. Humans have nicknamed corals after their resemblances to tree branches, stacked dinner plates, mushrooms, brains, and other unlikely items. But all reefs are formed by millions of tiny coral polyps—and the countless shells of their deceased predecessors.
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Mushroom Coral
Photograph by Carlos Bombardelli, My Shot
The mushroom coral uses this amazing Technicolor mouth to feast on something no other coral is known to favor—adult jellyfish. It’s thought that the corals simply wait for jellies to run into them, then snare them with stinging tentacles and shove them into their mouths. Unlike reef-building corals, mushroom corals—among the world’s biggest polyps at up to 12 inches (30 centimeters) wide—live as individuals.
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Damselfish on Coral Reef
Photograph by Paul Sutherland, National Geographic
Coral reefs teem with fish. Some are plankton eaters, others feed on corals, and “grazers” devour ocean vegetation like algae. Larger predators, like snappers and sharks, always stand at the ready to feast on smaller fish.
When humans overharvest reef fish species, the impact can be significant. The loss of “grazers,” for example, can cause algae populations to explode and spur bacteria growth that compromises coral health.
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Coral Reef
Photograph by Raul Touzon, National Geographic
Coral reefs are complex structures built by tiny organisms called coral polyps, which are kin to jellyfish and sea anemones. Polyps attach themselves to sunken rocks at the edges of islands or continents. Their limestone skeletons connect with one another in massive numbers to create first coral colonies, then larger reefs—Earth’s largest biological structures. A healthy coral reef can live for many thousands of years.
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Coral-Covered Anchor
Photograph by Raul Touzon, National Geographic
An 18th-century sailing ship dropped this anchor on a West Indies coral reef. Today’s human impacts aren’t always as obvious—but they are far more serious.
Pollution and overfishing can harm reef ecosystems locally. Climate change is causing trouble for reefs around the world, like coral bleaching episodes and increasingly acidic waters. Some scientists fear that 30 percent of the world’s reefs could be gone in 30 years.
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Coral
Photograph by Steve Ruddy, My Shot
Some living coral reefs probably began growing more than 50 million years ago. Today all reefs are an important part of the planet that many species depend on—including some 500 million humans. Reefs provide food for millions of people, protect coastlines from erosion, yield new medicines, and even stoke the engines of commerce. NOAA estimates that reefs contribute nearly $30 billion to the global economy each year.
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Great Barrier Reef
Photograph by David Doubilet, National Geographic
Coral reefs are found throughout the world’s tropical oceans, often in relatively shallow waters where algae use photosynthesis to covert the sun’s energy into vital nutrients. Australia’s incomparable Great Barrier Reef, pictured here, traces a graceful 1,250-mile-long (2,000-kilometer-long) arc off the nation’s northeast coast. This largest of all coral habitats—it covers an area larger than Poland—is actually made up of some 2,800 separate reefs.
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