Turning the Tide

The Tappan Zee Bridge, north of New York City, carried automobiles across the Hudson River for 62 years. In 2017, a new bridge replaced it. The old bridge was demolished. Workers picked apart the structure piece by piece.

Now those pieces are being recycled. Huge chunks of metal and concrete were cleaned. They were taken to one of several locations off the New York State coastline. Then they were dropped into the Atlantic Ocean. The old bridge is starting a new life as an artificial reef.

IT'S GOING DOWN A ship surveys what’s left of the old Tappan Zee Bridge (bottom) in early 2018, four days after it was demolished.

Under the Sea

Natural reefs are stonelike underwater ridges. They are made of living things called corals. The reefs serve as a habitat for marine life. They attract tourists to a region. This is good for local economies. Reefs also help prevent erosion × erosion BENTO FOTOGRAPHY/GETTY IMAGES the wearing away of land by the action of water, wind, or glacial ice (noun) Erosion is causing the river to become wider over time. . And they protect coastal communities from flooding. “Reefs are great for nature and for people,” Bill Ulfelder told TIME for Kids. He’s with the Nature Conservancy in New York.

But natural coral reefs are in trouble (see “Coral Crisis”). That’s why people are finding ways to build them from artificial materials. Artificial reefs aren’t made of coral. But they can provide many of the same benefits. Over time, coral may even grow on them.

SEA ART With more than 500 life-size sculptures, the Underwater Museum of Art, off the coast of Cancún, Mexico, is also a reef.

Ulfelder’s group works to renew New York waterways, which were harmed by pollution × pollution MILEHIGHTRAVERLER/GETTY IMAGES waste or poisons that are harmful (noun) A cloud of pollution filled the sky over the city. in the 20th century. In recent years, water quality has improved. Artificial reefs are bringing animals back to the area.

Help for Troubled Waters

Artificial reefs are created by placing large objects on the ocean floor. Sometimes, these objects are built to be used as reefs. They are often made of limestone, steel, and concrete.

KERPLUNK! A new artificial reef is lowered into the water near Marseille, France, on January 30, 2018.

A structure can also be recycled as a reef. That’s what happened with the Tappan Zee Bridge. Aircraft carriers, subway cars, and military tanks have all been reused this way. They are first cleaned of materials that could threaten ocean life.

Many artificial reefs are made from old ships. In 2005, Jim Walsh helped turn a ship called the Carthaginian II into a reef. It is off the coast of Hawaii. The reef is now a popular spot for scuba diving, fishing, and submarine tours.

The Carthaginian II landed on the ocean floor more than a decade ago. Back then, it was just a chunk of metal on a bare patch of sand. Now the ship is home to at least 75 animal species. They include unicorn fish, goatfish, and moray eels. “It’s amazing to see how much life is on that ship,” Walsh says.

Sidebar: Coral Crisis

When coral is healthy, tiny, colorful creatures called algae live on it. The coral protects the algae, and the algae are a food source for the coral. But when ocean water gets too hot or too cold, the algae leave the coral. Without algae, the coral has no food. It turns white. This is called coral bleaching. The world’s largest reef is the Great Barrier Reef, in Australia. About 93% of this reef has been harmed by coral bleaching. Scientists blame climate change and pollution.