Plastic waste floating in the ocean causes many problems for marine life: killing sea turtles that try to eat the debris or entangling whales and causing them to drown.
But there’s another impact people aren’t always aware of. As ocean plastic drifts with the currents, it can act like a tiny taxi that transports marine hitchhikers miles across the seas, sometimes taking them to places where they shouldn’t be.
“Floating marine debris, especially plastics, can persist at the sea surface for long periods and travel vast distances across oceans,” write the authors of a study published in the Marine Pollution Bulletin, which traced the journey of a 3.5cm bottle cap found off the coast of Japan.
To piece together the clues of where the bottle had come from, the researchers looked at the label, analysed environmental data including water temperature and salinity and examined all the organisms found on the cap under a microscope.
“The cap bore a label from a Philippine beverage company, indicating a likely origin from the Philippines or surrounding region,” says the study. This means the cap could have travelled hundreds of miles.
Perhaps even more noticeable than this epic journey was the passengers it carried along the way. The scientists found a 9cm tube-building polychaete worm (Eunice bipapillata) that had not been recorded in Japanese waters before.
The worm had “constructed a mucus tube enveloping much of the cap's interior,” according to the study. “This tube effectively transformed the smooth plastic cap into a complex three-dimensional habitat.”
Incredibly, there were 307 individual organisms living on the tiny bottle cap. “Overall, the bottle cap had effectively become a miniature reef, with the Eunice worm's tube providing structural habitat,” write the study authors.
“Inside, we found organisms that normally live in southern tropical waters,” says lead author Naoto Jimi, a lecturer at Nagoya University's Sugashima Marine Biological Laboratory, in a statement.
This included tiny filter feeding organisms called bryozoans, gooseneck barnacles and flatworms. The number of different organisms all thriving together on the bottle cap illustrate how plastic pollution can help invasive species spread to new regions.
“Geographic range extensions of some species may be occurring under the radar, so if this waste can be properly disposed, we may reduce the number of non-native species carried into new habitats,” adds Jimi.
This rafting behaviour isn’t unique to plastics – organisms can hitch a ride on items including algae and seagrass that drift along in the water – but plastic lasts much longer and the pollution problem is only getting worse.
More research is needed to understand how often this might happen and what the impacts are, according to the study, which writes: “even diminutive plastics can, at least occasionally, function as “miniature arks” capable of transporting a suite of taxa over oceanic distances.”
