NAGOYA - A bottle cap found drifting off Japan's western coast carried a tiny ecosystem of 307 creatures from waters near the Philippines, a study by Japanese researchers has found.
The cap, collected in waters off Kochi Prefecture in January 2023, likely traveled on the Kuroshio Current, a north-flowing, warm ocean current in the western North Pacific, for at least 70 days, according to the group led by Nagoya University.
The finding by the team of researchers from Kyoto University and institutions such as the Japan Agency for Marine-Earth Science and Technology also shows how even small pieces of marine litter can transport invasive species over long distances.
Some of the species found inside the cap are not seen in Japan.
Inside the 3.5-centimeter-diameter cap, a 9-centimeter-long ragworm had built an intricate nest from mucus and pebbles. The nest was also home to 306 other individual creatures, including foraminifera, barnacles, bryozoans and flatworms.
Comprising both coastal and open-ocean species, the find suggests that the cap had drifted through waters near the coast as well as the open sea.
A label of a Philippine beverage company attached to the cap suggested it had been discarded in or around the Southeast Asian country.
Analysis of oxygen isotope ratios in foraminifera shells, a technique used to reconstruct past water temperatures from shell chemistry, together with ocean-current simulations, indicated that the cap had passed through warmer waters around the archipelago.
Tracing such routes could help identify how invasive species enter new environments and how to prevent them from doing so, the researchers said.
"Even small pieces of garbage like bottle caps should not be taken lightly," said Naoto Jimi of Nagoya University's Sugashima Marine Biological Laboratory in Toba, Mie Prefecture. "Properly disposing them in trash bins helps protect ecosystems."
