What happens when a shipwrecks becomes a thriving marine habitat - The Washington Post

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Shipwrecks like that of the Titanic have long conjured tales of human courage and sacrifice, sunken treasure and unsolved mysteries.

But there are decidedly nonhuman stories as well in the estimated 3 million shipwrecks resting in shallow rivers and bays, coastal waters and the deep ocean across the globe.

Recently, I led an international team of biologists and archaeologists in disentangling the mysteries of how shipwrecks transform from wreckage to vibrant living seabed habitats. Our study, published today, describes how wrecked vessels can have second lives as seabed habitats and expands our understanding of shipwrecks by recognizing them as both cultural and biological resources.

The creatures that reside on and around sunken ships are so diverse and abundant that scientists often colloquially call such sites “living shipwrecks.” Marine life ranging from the microscopic to some of the largest animals in the sea use shipwrecks as homes.

Brilliantly colored corals and sponges blanket the wrecks’ surfaces, and silvery schools of baitfish dart and shimmer around the structures, chased by sleek, fast-moving predators. Sharks often cruise around wrecks, sometimes resting or looking for prey.

A second life for wrecks

Typically, ships are made of metal or wood. When a vessel sinks, it adds a 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.

A ship’s transformation from an in-service vessel into a thriving metropolis for marine life has a fairy-tale quality to it.

It begins when tiny microbes invisible to the naked human eye first 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 such as 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.

Hot spots for biodiversity

Shipwrecks host quantities and varieties of marine life that can make them hot spots for biodiversity.

The microbes that transform wreck structures 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 about 650 to 1,000 feet from the wreck. In the Atlantic Ocean, thousands of grouper, a type of reef fish highly valued by fishers, congregate around and inside shipwrecks.

Shipwrecks can also serve as steppingstones across the ocean floor that animals use as temporary homes while moving from one location to another. This has been documented in areas of the world with dense concentrations of shipwrecks, such as off North Carolina, where storms and war have sunk hundreds of ships.

In this part of the ocean, popularly known as the “Graveyard of the Atlantic,” reef fish likely use the island-like shipwrecks as corridors when moving north or south away from the equator to find favorable water temperatures as climate change warms the oceans. Scientists have also observed sand tiger sharks traveling from one wreck to another, possibly using the shipwrecks like migration rest stops.

In the deep sea, life growing on shipwrecks even can 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 wreck of the steel luxury yacht Anona.

Biological mysteries abound

Despite their biological value, shipwrecks can also threaten underwater life by altering or destroying natural habitats, causing pollution and spreading invasive species.

When a ship sinks, it can damage existing seafloor habitats. In a well-documented case in the Line Islands of the central Pacific, an iron shipwreck sank on a healthy coral reef. The iron infusion substantially decreased coral cover, and the reef was overcome by algae.

Ships can also carry pollutants as fuel or cargo. As shipwrecks deteriorate in seawater, there is a risk that these pollutants may be released. The level of risk depends on how much of the pollutant the ship was carrying and how intact the wreck is. One recent investigation revealed that effects from shipwreck pollutants can be detected in microbes up to 80 years after a wreck.

Shipwrecks may also inadvertently assist the spread of invasive plants and animals that wreak biological havoc. Invasive cup coral has spread on World War II shipwrecks off Brazil. In Palmyra Atoll in the Pacific, a type of anemone called a corallimorph rapidly invaded a shipwreck and now threatens 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 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 also to better understand their biology.

Maximizing discovery will require biologists, archaeologists and engineers to work together to explore these special habitats. Ultimately, the more we learn, the more effectively we can conserve these historical and biological gems.

Avery Paxton is a research marine biologist at the National Oceanic and Atmospheric Administration. This article was produced in collaboration with theconversation.com.

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