Why plastic-filled ‘Neptune balls’ are washing up on beaches

In 2018 and 2019, Sanchez-Vidal’s team examined seagrass balls washed up on four beaches on the island of Mallorca, Spain. On the shores of Sa Marina, Son Serra de Marina, Costa dels Pins and Es Peregons Petits, they found plastic debris in half of the loose seagrass leaf samples, up to 600 fragments per kilogram (2.2lb) of leaves.

Only 17% of Neptune balls contained plastic, but where it was found it was densely packed – nearly 1,500 pieces per kilogram. Tighter bundled balls were more effective at trapping plastic.

“After our paper was published, a lot of people started sending me [pictures of] monster Neptune balls,” says Sanchez-Vidal. These are balls that capture larger and more visible pieces of plastic.

“Sometimes they had sanitary towels, tampons, wet wipes – things with a lot of cellulose, so they sink,” she explains: “No, I didn’t really want to receive those pictures from everybody,” she jokes.

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