Every year, thousands of shipping containers are lost to the briny deep. Maggie Koerth-Baker on the strange new homes they create for marine creatures.

Ten years ago, a steel box the size of a whale shark fell off the deck of a commercial shipping vessel and sank through more than 4000 feet of water, to rest at the bottom of California's Monterey Bay.

Shipping containers like this one are lost in the ocean all the time, as many as 10,000 fall overboard every year. While they still float, those containers create hazards for smaller boats. When they settle on the seafloor … well, nobody really knows exactly what happens. At least, not in the long term. And that's what makes the shipping container lost in Monterey Bay special. Falling within the boundaries of the Monterey Bay National Marine Sanctuary, it was found by scientists, who have been studying it ever since. Back in 2011, I interviewed Andrew DeVogelaere, the sanctuary's research coordinator, about why scientists were so interested in sunken shipping containers. Now, the first scientific research paper on the container has been published. The big questions the scientists have will take more years of study to answer, but this first paper is important if, for no other reason, than the fact that it highlights how little we know about the deep ocean floor, in general.

As scientists study this shipping container, what they're really studying is the life forms that grow around it and on it. When a shipping container hits the ocean floor, it crushes anything it lands on like Dorothy's house in The Wizard of Oz. And, theoretically, its presence affects what grows in that area (and when it grows) for many years to come.

That theory is based off of what happens around artificial reefs, says Josi Taylor, a postdoctoral fellow at the Monterey Bay Aquarium Research Institute and the lead author on the recently published paper. Used to increase the presence of marine life, artificial reefs can really be anything from stacks of concrete blocks, to scuttled ships, to piles of old tires. "If a physical object is down there, animals will be drawn to it because it provides a place to hide from predators. And then predators will be drawn to that. You'll find life around just about anything you put down there," Taylor said.

But some objects do a better job of functioning as healthy artificial reefs than others. The aforementioned pile of tires, for instance, was a popular idea in the 1970s. Later, though, it turned out that sunken tires were leaching plastic compounds called PCBs into the water. Those compounds can cause cancer in animals, so the tire reefs, while attracting wildlife, were also, probably, killing some of that life over time.

That's not the only potential risk of artificial reefs, said Peter Macreadie, a marine ecologist at the University of Technology, Sydney, Australia. Besides the potential for contaminates which can work their way up the food chain, artificial reefs could also accidentally alter the local food webs. If the reef helped to boost the numbers of a previously low-population predator, for instance, that animal could end up eating itself out of house and home. And scientists are also concerned about the risk of artificial reefs acting as stepping stones — points of intense biological activity that serve as oases on an otherwise unvegitated deep-sea floor. Given enough stepping stones, animals might be able to cross from their native waters, one step at a time, to become invasive species somewhere else.

That last concern is actually one of the big reasons scientists are interested in what happens in and around sunken shipping containers. More than other artificial reefs, the high numbers and global ubiquity of containers could make them particularly likely to function as stepping stones from one ecological environment to another.

The Monterey Bay shipping container is the only one of its kind that's been found and monitored by scientists. In the new paper, the researchers were able to document that life on the shipping container varied quite a bit compared to the soft, sandy, featureless seafloor nearby. Tube worms, scallops, and snails — animals not found at all on the seafloor — lived in big-city density on the container. But while there were a higher number of animals per square foot on the container, the seafloor was home to a much higher diversity of life.

What's more, that mix of worms and mollusks hanging out on the container was very different from the life associated with natural rocks and other hard surfaces in the same region of ocean. There, you find a lot of small fish, jellies, sponges, and starfish — none of which seemed to live around the container.

That doesn't necessarily mean the container is producing an anomalous, unhealthy ecosystem, however. Those natural rocky spots have tube worms and snails, too. Huge numbers of them. It's completely possible that what we're seeing on the container is an early stage of animal colonization that will, eventually, end up looking a lot like what already exists in natural hard-surface ecosystems, said Taylor, Macreadie, and Andrew DeVogelaere.

But here's the catch: It's hard to know whether that is the case because nobody has really studied the deep sea over time to see that process in action. "I don't think we really know about the animal populations in the deep sea," Macreadie said. "We often take advantage of deep sea coring programs to look for samples. They'll come back with bucketloads of new species. There are plenty of animals being dug that haven't been seen before. We're at an early stage of understanding oceans."

Nobody knows exactly what life was like on the seafloor in Monterey Bay before the shipping container dropped in. Nobody knows what the process looks like over time when animals colonize a hard surface in deep ocean. And both those facts make it difficult to take the data collected by Josi Taylor's team and say much about it beyond "this is what has happened over the last 10 years" and "it doesn't look too alarming".

Those are fairly boring-sounding conclusions, but they're also easily misinterpreted. For one thing, a lack of Earth-shattering pronouncements doesn't mean the research isn't important. In fact, the opposite is true. It's rare for a team to be able to track a specific location in the deep ocean as long as the MBARI container has been tracked, Macreadie said. When his team studies artificial reefs elsewhere in the world, they often have only three years to get a quick snapshot of what's happening. At this point, we're talking about a subject of which there is so little data that this research is as much about establishing what is "normal" than anything.

Second, the results of this study definitely shouldn't be taken as a sign that it's okay to lose shipping containers willy-nilly in the deep ocean. Part of the funding for MBARI's study comes from fines the shipping company paid for allowing containers to fall overboard into a marine reserve. There is a risk, Macreadie said, that somebody could look at a preliminary study like this one and use it to claim that the 10,000 shipping containers lost every year are benign, or even a good thing. The truth, he said, is that we don't really know yet what effects this container will have on local ecosystems in the long run. Based on what we do know about artificial reefs, though, it's safe to assume that some of those effects will be positive and some will be negative. What's more, when the artificial reefs in question are being deposited in high numbers without any planning for location, there is a serious risk of not-so-nice unintended consequences. "For an artificial reef to be beneficial there needs to be some kind of regulation," he said. "The best case scenario is to have research investigating what might happen and to have a contingency plan, like enough money to rip things back out, if it goes wrong." None of that is true when you're talking about a shipping container at the bottom of the ocean.

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Photo: Bernd Zimmermann