People have been sailing the world’s oceans for thousands of years, but not all of them have reached port. Researchers estimate that there are approximately three million shipwrecks worldwide, located in shallow rivers and bays, coastal waters and the deep ocean. Many sank during catastrophes – some during storms or after running aground, others during battles or collisions with other ships.
Shipwrecks such as the RMS Titanic, RMS Lusitania and USS Monitor evoke stories of human courage and sacrifice, sunken treasure and unsolved mysteries. But there’s another angle to their stories that don’t involve people.
I have studied the biology of shipwrecks in the United States and internationally for fourteen years. From this work I have learned that shipwrecks are not only cultural icons, but can also be biological treasures that create a habitat for diverse communities of marine life.
I recently led an international team of biologists and archaeologists in unraveling the mysteries of how this transformation occurs. Based on scientific advances from our team and international colleagues, our new research describes how wrecked ships can find a second life as seabed habitat.
A new home for marine life
Ships are usually made of metal or wood. When a ship sinks, it adds a strange, artificial structure to the seabed.
For example, the World War II tanker EM 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 seabed like an underwater skyscraper, creating an island oasis in the sand.
The creatures that live on and around sunken ships are so diverse and abundant that scientists often colloquially call these places “living shipwrecks.” Marine life, ranging from microscopic critters to some of the largest animals in the sea, uses shipwrecks as their home. Brilliantly colored corals and sponges cover the surfaces of the wrecks. Silvery schools of baitfish dart and glitter around the structures, pursued by sleek, fast-moving predators. Sharks sometimes cruise around wrecks, probably resting or looking for prey.
The origin of a second life
The transformation of a ship from a working vessel to a thriving metropolis for marine life can seem like a fairy tale. It has an origin story that once occurred – the devastating event – and a succession of life that arrives on the submerged structure and begins to flourish.
Tiny microbes invisible to the naked human eye initially settle on the wreck surface, forming a carpet of cells called a biofilm. This coating helps make the wreck structure suitable for larval animals such as sponges and corals to settle and grow there.
Diverse marine life lives on the 19th-century wooden-hulled wreck of the Ewing Bank, which lies 2,000 feet (610 meters) deep in the Gulf of Mexico. NOAA
Larger animals such as fish sometimes appear within minutes of a ship sinking. Small fish hide in the cracks and crevices of the structure, while large sharks glide around them. Sea turtles and marine mammals such as fur seals have also been spotted on wrecks.
Biodiversity hotspots
Shipwrecks are home to quantities and varieties of marine life, which can make them biodiversity hotspots. The microbes that turn the wreck structure into a habitat also enrich the surrounding sand. Evidence from wrecks in the deep Gulf of Mexico shows that a halo of increased microbial diversity radiates outward somewhere between 200 and 300 meters from the wreck. In the Atlantic Ocean, thousands of groupers, a type of reef fish highly prized by fishermen, gather around and in shipwrecks.
Groupers and a conger eel, bottom center, on the wreck of the German submarine U-576 off the coast of North Carolina. NOAA
Shipwrecks can also serve as stepping stones across the ocean floor that animals use as temporary shelters as they move from one location to another. This has been documented in areas of the world with dense concentrations of shipwrecks, such as North Carolina, where storms and war have sunk hundreds of ships.
In this part of the ocean, colloquially known as the ‘graveyard of the Atlantic’, reef fish likely use the island-like shipwrecks as corridors as they travel north or south, away from the equator, to find favorable water temperatures while the climate change is warming the oceans. Scientists have also observed sand tiger sharks traveling from one wreck to another, possibly using the shipwrecks as resting places during migration.
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 harbor symbiotic bacteria that produce chemical energy. Such tubeworm colonies have been documented in the Gulf of Mexico on the steel luxury yacht Anona.
Biological mysteries abound
Despite their biological value, shipwrecks can also threaten marine life by altering or destroying natural habitats, causing pollution and spreading invasive species.
When a ship sinks, it can damage existing habitats on the seabed. In a well-documented case in the Line Islands in the central Pacific Ocean, an iron shipwreck sank on a healthy coral reef. The iron infusion significantly reduced coral cover and the reef became overwhelmed by algae.
Ships can carry pollutants as fuel or cargo. As shipwrecks deteriorate in seawater, there is a risk of these pollutants being released. The level of risk depends on how much of the pollutant the ship was carrying and how intact the wreck is. A recent study found that the effects of pollutants from shipwrecks can be detected in microbes up to 80 years after the wreck.
Shipwrecks can also inadvertently contribute to the spread of invasive plants and animals that cause biological damage. Wrecks are new structures where invasive species can settle, grow and use as a hub to expand into other habitats. Invasive cup coral has spread across World War II shipwrecks off the coast of Brazil. On the Pacific Ocean’s Palmyra Atoll, a type of anemone called a corallimorph quickly invaded a shipwreck and is now threatening healthy coral reefs.
The future of shipwreck research
Shipwrecks create millions of study sites that scientists can use to ask questions about marine life and habitats. One of the biggest challenges is that many wrecks are undiscovered or in remote locations. Technological advances can help researchers explore the most inaccessible parts of the ocean, not only to find shipwrecks but also to better understand their biology.
To maximize discovery, biologists, archaeologists and engineers will need to work together to explore these special habitats. Ultimately, the more we learn, the more effectively we can preserve these historical and biological gems.
This article is republished from The Conversation, an independent nonprofit organization providing facts and analysis to help you understand our complex world.
It was written by: Avery Paxton, National Oceanic and Atmospheric Administration.
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Avery Paxton is affiliated with NOAA National Centers for Coastal Ocean Science.
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