The rapid rise in cargo ship traffic this century has introduced a new form of waste to the ocean: the shipping container.
There are 5-6 million containers in transit across the world's oceans at any one time; estimates are that as many as 10 000 of these fall overboard every year, causing financial losses in the region of $370 million (R400 million).
They are lost because of rough seas, and because they are difficult to secure, stacked in top-heavy piles on ships.
The number of container ships and trips they make, and thus numbers of containers that will be lost, is rising along with globalisation, the growing world population and the ever-greater demand for goods.
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Containers have widely variable contents, some of which are toxic.
Their exteriors are also coated with paints of varying toxicity. Scientists think containers may take centuries to erode in the ocean.
Floating containers pose a potential collision risk for shipping and recreational ocean users. Some fetch up on beaches, where they may also pose health and environmental risks.
But until now there's been little evidence of the effect lost containers might be having on the deep sea and ocean floor, where most of them are likely to end up.
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Sunken treasure for scientists
When one of these lost containers was found in the Monterey Bay National Marine Sanctuary off the west coast of California, it offered scientists from the Monterey Bay Aquarium Research Institute (MBARI) a unique opportunity to study its impact.
The container (and several of its mates) had been washed off the deck of a Taiwanese vessel during a storm in 2004.
The scientists were interested in basically two aspects: do containers release toxins, and how does a massive metal cube settling on the ocean bed affect marine life?
Man-made objects that sink to the ocean floor may be partly beneficial in that they offer new surfaces to which some organisms can attach, and new nooks and crannies in which others can hide.
This is the thinking behind artificial reefs, created to replace coral and other natural substrates that have been lost to environmental degradation.
One of the best examples of an artificial reef is the extraordinary underwater artwork The Silent Evolution, off the coast of Cancun, Mexico, which is being progressively transformed by sea life that makes its home on the man-made statues.
Credit: Jason deCaires Taylor
Read more about The Silent Evolution.
In a recent paper in the Marine Pollution Bulletin, The MBARI scientists reported that the container did attract colonisers to a certain extent, and some of these, like sea snails and scallops, were similar to those on surrounding rocky surfaces.
However, the diversity and abundance of animals was significantly lower on the container up to 10m around it, compared with 500m away.
Further research is needed to work out why this may be so - it could be because of toxins from the container, or because the organisms need more time for the colonisation process to catch up with the surrounding undisturbed area.
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De Caires Taylor, J. Official web site for The Silent Evolution. View more galleries by the artist here.
Taylor, JR et al. Deep-sea faunal communities associated with a lost intermodal shipping container in the Monterey Bay National Marine Sanctuary, CA Marine Pollution Bulletin
Olivia Rose-Innes is Health24’s EnviroHealth Editor. Read more of her columns and articles or post a question to her expert forum.