Humans have sailed the world’s oceans for thousands of years, but they haven’t all reached port. Researchers estimate that there are some three million shipwrecks worldwide, resting in shallow rivers and bays, coastal waters and the deep ocean. Many sank during catastrophes – some during storms or after running aground, others in battle or collisions with other vessels.
Shipwrecks like the RMS Titanic, RMS Lusitania and USS Monitor conjure tales of human courage and sacrifice, sunken treasure and unsolved mysteries. But there’s another angle to their stories that doesn’t feature humans.
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A NEW HOME FOR UNDERWATER LIFE
Ships are typically made of metal or wood. When a vessel sinks, it adds foreign, artificial structure to the seafloor.
For example, the World War II tanker E.M. Clark sank on a relatively flat, sandy seabed in 1942 when it was torpedoed by a German submarine. To this day, the intact metal wreck looms over the North Carolina seafloor like an underwater skyscraper, creating an island oasis in the sand.
The creatures that reside on and around sunken ships are so diverse and abundant that scientists often colloquially call these sites “living shipwrecks.” Marine life ranging from microscopic critters to some of the largest animals in the sea use shipwrecks as homes. Brilliantly colored corals and sponges blanket the wrecks’ surfaces. Silvery schools of baitfish dart and shimmer around the structures, chased by sleek, fast-moving predators. Sharks sometimes cruise around wrecks, likely resting or looking for prey.
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THE ORIGIN OF A SECOND LIFE
A ship’s transformation from an in-service vessel into a thriving metropolis for marine life can seem like a fairy tale. It has a once-upon-a-time origin story – the wrecking event – and a sequence of life arriving on the sunken structure and beginning to blossom.
Tiny microbes invisible to the naked human eye initially settle on the wreck’s surface, forming a carpet of cells, called a biofilm. This coating helps to make the wreck structure suitable for larval animals like sponges and corals to settle and grow there.
Larger animals like fish sometimes appear within minutes after a ship sinks. Small fish hide in the structure’s cracks and crevices, while large sharks glide around it. Sea turtles and marine mammals such as fur seals have also been spotted on wrecks.
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HOT SPOTS FOR BIODIVERSITY
Shipwrecks host quantities and varieties of marine life that can make them hot spots for biodiversity. The microbes that transform the wreck structure into habitat also enrich the surrounding sand. Evidence from deep Gulf of Mexico wrecks shows that a halo of increased microbial diversity radiates outward anywhere from 650 to 1,000 feet (200-300 meters) from the wreck. In the Atlantic Ocean, thousands of grouper, a type of reef fish highly valued by fishers, congregate around and inside shipwrecks.
In the deep sea, life growing on shipwrecks can even generate energy. Tube worms that grow on organic shipwreck materials such as paper, cotton and wood host symbiotic bacteria that produce chemical energy. Such tube worm colonies have been documented in the Gulf of Mexico on the steel luxury yacht Anona.
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THE FUTURE OF SHIPWRECK EXPLORATION
Shipwrecks create millions of study sites that scientists can use to ask questions about marine life and habitats. One of the greatest challenges is that many wrecks are undiscovered or in remote locations. Advances in technology can help researchers see into the most inaccessible areas of the ocean, not only to find shipwrecks but to better understand their biology.
Ultimately, the more we learn, the more effectively we can conserve these historical and biological gems.