For a decade or more, scientists have assumed our seas carry millions of tons of plastic, much of which should be floating in open water, forming vast midocean "gyres" — islands of man-made mess such as the Great Pacific Garbage Patch. But according to a new study, something more worrying is happening to 99 percent of the ocean's plastic: it's disappearing.

The study outlines the findings of scientists who trawled the waters around five large ocean gyres in 2010 and 2011. The data they obtained put them far short of the expected amount of plastic in the ocean — rather than millions of tons, the global load of ocean plastic was calculated at 40,000 tons at most. Carlos Duarte, an oceanographer at the University of Western Australia and co-author of the study, said that the findings mean we "can't account for 99 percent of the plastic that we have in the ocean."

The missing plastic could have been eaten by ocean animals

Most of the ocean's plastic is expected to be microscopic in size, after having been broken down by the action of waves and radiation from the sun, but the scientists behind the study used very fine mesh nets that should have been able to pick up even these minuscule fragments. Instead, scientists have to consider other destinations for our garbage. Duarte thinks the missing millions of tons could be entering the stomachs of marine animals.

We don't know the consequences of animals eating ocean plastic

"There is potential," Duarte says, "for this plastic to enter the global ocean food web." Duarte notes that we are part of the same food web as the plastic-gobbling fish, but we don't know how damaging this could be for our ecosystem. Speaking to Science, Peter Davison, oceanographer at California's Farallon Institute for Advanced Ecosystem Research, said plastics could "suck up all the pollutants in the water and concentrate them" in the food chain, or fish could be "puking or pooping" the plastic out, leading to no long-term damage.

Davison notes the missing plastic could also be dragged down by the weight of animal feces clinging to it or organisms growing on it, washing ashore, or breaking down even further so as to be undetectable, but he says the fact that fish and other marine creatures are eating our plastic waste is "indisputable." With millions of tons of plastic going unaccounted for in our oceans, and the uncertain consequences of animals ingesting such material, the scientists agree more research is needed.