Ocean Litter Gives Alien Species an Easy Ride

Hillary Mayell
for National Geographic News
April 29, 2002

Alien species are using trash in the ocean to raft their way to new territory, where they can colonize and possibly overwhelm local marine ecosystems, reports a British marine biologist.

This kind of dispersal is not a new phenomenon. Aquatic animals have long used wood, pumice from volcanic eruptions, coconut shells, and the like as mobile homes for transport. But the huge increase in the availability of human debris is providing many more opportunities for invaders to colonize.

"The debris is their commercial jetliner, paralleling the 30-year explosion of travel among people. The opportunity being provided by the sheer amount of debris is unparalleled in geological time," said David Barnes, a marine biologist with the British Antarctic Survey.

Barnes found that the amount of garbage, particularly plastic, floating in the ocean has enabled travel by marine species to roughly double in the subtropics and more than triple at high latitudes. The findings of the ten-year study are published in the April 25th issue of the journal Nature.

Alien species introduced into new habitats—intentionally or unintentionally—pose a major threat to global biodiversity.

The newly adopted habitats of non-native plants and animals often lack the natural enemies of these species, allowing them to multiply and spread quickly.

Alien species can devastate ecosystems by eating the native species, competing with them for food or habitat, introducing fatal diseases, or decreasing genetic diversity by mating with the native species.

Rafting the Oceans on Plastic

The small marine animals that hitch rides across the ocean are typically non-mobile. They spend most of their lives attached to rocks, plants, shells, and other surfaces. The alien invaders include bryozoans, barnacles, polychaete worms, hydroids, crabs, and mollusks—"the range of organisms is enormous," said Barnes.

Besides a big increase in the amount of debris floating in the oceans, the kind of debris has changed too. Plastic is much more durable and longer lasting. "Organisms like colonizing on plastic—it's a good surface to attach to," said Barnes. "It's not slippery like glass, it doesn't rot like wood, and it travels slower than a ship's hull."

And plastic acts like a floating hotel, transporting the organisms to areas they would never be able to reach on their own.

"Say you're standing in Miami and you chuck or accidentally drop a bottle of lemonade into the ocean," said Barnes. "The larvae in the water settle on the plastic, and the bottle has so much buoyancy it can really hold an enormous number of these creatures.

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