Scuba diving scientists explore the newly found coral reef near Tahiti.

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NCSS: People, Places, and Environments • Science, Technology, and Society • Global Connections

GEOQUEST

Scale Maps

Discovery In the Deep

Climate change is threatening the planet’s coral reefs. But the recent discovery of a thriving reef in the South Pacific is offering hope for these irreplaceable ocean treasures.

Last fall, scientists diving in the waters near Tahiti, an island in the Pacific Ocean, discovered something remarkable—a coral reef “stretching as far as the eye can see,” as one diver said. 

Moreover, it seemed to be in perfect condition—making the nearly 2-mile-long wonder one of the largest known healthy coral reefs on Earth. (Climate change, pollution, and other threats have caused damage to most coral reefs worldwide.) The discovery has thrilled experts who study coral reefs—and hope to save them.

Rainforests of the Sea

Coral reefs grow along shorelines around the globe. The largest ones are found in warm, tropical waters near the equator (see map, below)

A coral can be made of up to thousands of tiny jellyfish-like animals called polyps. Each polyp grows a hard shell known as an exoskeleton for protection. A reef begins when a baby coral, called a larva, attaches itself to a hard surface. Additional coral larvae latch on, and bit by bit, over thousands of years, they form a reef.

Coral reefs cover less than 1 percent of the ocean floor. But they provide a home and a food source for about a quarter of all marine animal species and a wide variety of plant life. The most diverse ecosystems on the planet, reefs are often called “the rainforests of the sea” by scientists.

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Algae provide corals with food and give them their color. Loss of algae leads to coral bleaching, a warning sign that a reef is at risk.

Threats of Climate Change

Yet today, coral reefs are “the most endangered group of animals on the planet,” says biologist Nancy Knowlton of the Smithsonian Institution. 

One major threat comes from carbon dioxide (CO2), a greenhouse gas that is produced when humans burn fossil fuels to power homes, cars, and businesses. Oceans have absorbed much of the excess CO2 that has built up in the atmosphere in recent decades. The gas turns ocean water acidic, which makes it hard for corals to build shells. This causes coral reefs to break down. 

Increased CO2 in the atmosphere has also been a major contributor to climate change, which has raised ocean temperatures. Corals rely on tiny plantlike algae that live inside them to produce much of their food. But when seawater becomes too warm, the algae stop making food—or even die—threatening reefs with starvation. One recent study estimates that half of the coral reef area on Earth has vanished since the 1950s. This threatens the vast number of species that depend on reefs—including human beings. Coral reefs are sources of food for about 1 billion people around the world. 

Discovering Hope

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Coral reefs are made up of many different kinds of coral colonies growing next to and on top of each other.

All that makes the recent discovery near Tahiti especially exciting. Tahiti is the main island in French Polynesia (see map, below). Experts believe the reef there continues to thrive because it is located deep enough—100 to 210 feet below the ocean’s surface—to escape warming temperatures. 

The find serves as a reminder that other healthy reefs may yet exist. And it offers hope to researchers who are working on ways to help reefs make a comeback. For instance, some scientists are trying to breed heat-resistant corals, with the goal of implanting them in damaged reefs to nurse those reefs back to health. 

Still, Knowlton says, there is just one real long-term way to preserve these precious ecosystems: slowing climate change. Only by ending our reliance on fossil fuels, she says, can coral reefs be saved.

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