"The bottle travels with the trade winds and prevailing ocean currents, and winds up on the west coast of Scotland or Ireland," he said. "Now you've got lots of adult colonists, and they're spawning all the time. The new larvae might not survive because the conditions are too different from their native habitat, or they could just settle in the new environment and not make much difference at all."
What his paper warns about, Barnes said, "are the ones that settle and could eat the native species, or outcompete them for space."
Allen Collins, a marine biologist at the University of California at San Diego, said the study raises a lot of questions.
"Are the organisms traveling on [man-made] debris different from those that use natural floats? It makes sense that the rate of invasion can go up with an increase in opportunity," he said. "But if the organisms wind up in a very different environment, it's very unlikely they could survive. So it's unclear how much of an impact in terms of species invasion there might be. "
Travel to New Places
According to Barnes, the rubbish is carrying the marine organisms to new places.
Thousands of species of marine organisms move around the world on ship bottoms; the Ecological Society of America estimates that more than 10,000 marine species each day may hitch rides around the globe in the ballast water of cargo ships.
"But the ships have been plying these trade routes for a long time," said Barnes. "Traveling the same routes, you could imagine much of the damage has already been done."
The Southern Ocean may be particularly vulnerable. The amount of debris found in parts of Antarctica increased 100-fold during the early 1990s, said Barnes. Because of its isolation, the fauna is highly endemic and therefore may be more subject to being pushed out by invaders.
At the same time, global warming may reduce the natural protection that freezing temperatures provide by inhibiting colonization by many alien species.
The increase in debris poses other problems besides the threat of colonization by alien species.
"Even in the remotest parts of the planet, we see garbage, plastic bottles, cigarette lighters," said Iain Kerr, a member of the Odyssey team, a five-year research effort to collect data on whales in the world's oceans. "Albatrosses are feeding their chicks cigarette lighters because they resemble the pumice they eat to help digestion. So you have chicks dying from over-consumption of cigarette lighters. The plastic is everywhere."
Anyone interested in contributing data to the ongoing study by conducting simple surveys of shore debris should contact David Barnes at: firstname.lastname@example.org. He is particularly interested in data from the following islands: Andamans, Ille Amsterdam, Bermuda, Chagos, Clipperton, Cocos/Christmas, Gilbert, Midway, Society, Socotra, Trinidade (an island off the coast of Brazil), and Wake.
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