"It's becoming more effective than bilge water and ships as a mechanism of bringing exotics to foreign locations," Moore said.
Packed with Plastic
Safina said plastic is also nothing but trouble for a host of marine organisms.
For example, seabirds like the North Pacific albatross are often found dead with innards full of plastic.
"I'm talking about chunks of plastic. I'm talking about being packed with cigarette lighters. I'm talking about toothbrushes," Safina said. "Horrific things that you can't believe are inside of birds."
Safina is unsure why the birds eat the plastic, but he suggests they may be attracted to it for the same reason that they are drawn to pumice stones and driftwood: Fish eggs and fleshy barnacles are often attached to such floating items.
Once the seabirds digest the food on the stones and driftwood, they cough up the debris.
"I think they probably transferred that to plastics," Safina said. "I don't think they are mistakenly thinking that plastic is food, although that's possible."
He once saw an albatross unsuccessfully try to cough up a toothbrush.
Sea turtles, however, do mistake plastic bags for food, most likely jellyfish, Safina added. Sea turtles are often found dead with their intestines clogged by plastic bags. (See photos of sea turtles.)
"It probably looks enough and feels enough like jellyfish that, even though it doesn't taste like much of anything, they just think they should eat it," Safina said.
(Read related story: "Are Plastic Grocery Bags Sacking the Environment?" [September 2, 2003].)
Moore, of the Algalita Marine Research Foundation, estimates that over the past 50 years, more than a hundred million tons of plastic debris have accumulated in the world's oceans.
"It's not just on the surface or the bottom; it's throughout the water column. And it's in all parts of the ocean. There's no part of the ocean in which plastic debris has not permeated," he said.
(Learn more about pollution and other threats to the world's oceans.)
What's more, he added, the problem is getting worse, increasing by a factor of ten every two to three years.
Fortunately, he added, the issue is gaining recognition. For example, San Francisco's Board of Supervisors last month voted to ban large supermarkets from using plastic bags.
"It's all coming to a head," Moore said. "People are just fed up with living in a soup of toxic trash."
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