by 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 around three million shipwrecks around the world, resting in shallow rivers and bays, in coastal waters and in the deep ocean. Many sank during disasters – 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 tell stories of courage and human sacrifice, sunken treasure and unsolved mysteries. But there is another angle to their stories that is not about people.
I have studied the biology of shipwrecks in the United States and internationally for the past 14 years. From this work, I have learned that sunken ships are not only cultural icons but can also be biological treasures that create a habitat for various communities of underwater life.
Recently, I led an international team of biologists and archaeologists to unravel the mysteries of how this transformation occurs. Drawing on scientific advances from our team and international colleagues, our new study describes how wrecked vessels can have a second life as habitats on the seabed.
A new home for underwater life
Ships are usually made of metal or wood. When a vessel sinks, it adds a foreign, 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 call these sites “living shipwrecks”. Marine life, from microscopic critters to some of the largest animals in the sea, use shipwrecks as homes. Brilliantly colored corals and sponges make up the surfaces of the broken dies. Silvery schools of bait darts and shimmer around the structures, chased by fast moving predators. Sometimes sharks cruise around wrecks, probably resting or looking for prey.
The origin of the second life
The transition of a ship from a serviceable vessel to a thriving seafaring metropolis seems like a fairy tale. It has a one-off origin story – the destruction event – and a sequence of life finding the sunken structure and beginning to flourish.
Tiny microbes invisible to the human eye first settle on the exposed surface of the rake, forming a carpet of cells, known as a biofilm. This coating helps make the reef structure suitable for larval animals such as sponges and corals to settle and grow there.
Sometimes larger animals such as fish appear within minutes of a ship sinking. Small fish hide in the cracks and crevices of the structure, and large sharks glide around it. Sea turtles and marine mammals such as fur seals can also be seen on wrecks.
Biodiversity hotspots
Shipwrecks support quantities and types of marine life that can be hotspots for biodiversity. The microbes that transform the structure of the wreck in its habitat also enrich the surrounding sand. Evidence from deep Gulf of Mexico shipwrecks shows that a web of increased microbial diversity radiates out anywhere from 650 to 1,000 feet (200-300 meters) from the wreck. In the Atlantic Ocean, thousands of groupers, a type of reef fish prized by fishermen, congregate around and within shipwrecks.
Shipwrecks can be steps across the ocean floor that animals use as temporary homes as they move from one place to another. This has been documented in areas around the world where there are large numbers of shipwrecks, such as off North Carolina, where storms and war have engulfed hundreds of ships.
In this part of the ocean, commonly known as the “Graveyard of the Atlantic”, reef fish probably use island wrecks as corridors as they move north or south of the equator to find favorable water temperatures as climate change affects the oceans. Scientists have also observed sand tiger sharks traveling from one wreck to another, possibly using wrecks as rest stops during migration.
In the deep sea, life growing on shipwrecks can even generate energy. Tubeworms that grow on organic shipwrecks such as paper, cotton and wood form symbiotic bacteria that produce chemical energy. Colonies of such tube worms have been documented in the Gulf of Mexico on the luxury steel yacht Anona.
There are many biological mysteries
Despite their biological value, shipwrecks can also threaten underwater life by altering or destroying natural habitats, leading to pollution and the spread of invasive species.
When a ship sinks, it can damage existing seabed habitats. In a well-documented case in the Line Islands in the mid-Pacific, an iron shipwreck sank a healthy coral reef. The iron infusion significantly reduced coral cover, and algae overwhelmed the reef.
Ships may 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 secure the wreck is. One recent investigation showed that effects from shipwreck pollutants can be detected in microbes up to 80 years after the ship.
Shipwrecks may also inadvertently contribute to the spread of biologically damaging invasive plants and animals. Wrecks are new structures that invasive species can settle on, grow and use as a hub to spread to other habitats. A cup of invasive coral has spread over World War II sunken ships off Brazil. In Palmyra Atoll in the Pacific Ocean, a type of anemone called a corallimorph has rapidly invaded a shipwreck and is now threatening healthy coral reefs.
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 biggest challenges is that many wrecks are either undiscovered or in remote locations. Advances in technology can help researchers look into the most inaccessible areas of the ocean, not only to find shipwrecks but to better understand their biology.
To maximize discovery it will be necessary for biologists, archaeologists and engineers 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, a non-profit, independent news organization that brings you facts and analysis to help you make sense of our complex world.
It was written by Avery Paxton National Oceanic and Atmospheric Administration.
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Avery Paxton is affiliated with NOAA’s National Centers for Coastal Ocean Science.
