OUR hunt has got off to a slow start. When the sea is choppy, spotting our quarry is hard. But as the sun rises higher, our efforts are finally rewarded. Shielding her eyes against the light bouncing off the water, Tjaša Kogovšek points to a faint dark blob. Our boat moves closer, and she plunges her net in to scoop the creature into a white bucket. We have bagged our first trophy of the day.

I am in the Gulf of Trieste off the coast of Slovenia catching jellyfish with researchers from the country’s National Institute of Biology. Knowing their catch will ultimately die, Kogovšek has mixed feelings about the hunt. “At the beginning it was very difficult,” she says, “because their destiny is not nice after they are in my hands.” But she is also well aware that an explosion in jellyfish numbers in recent years is a serious problem, both for us and for the marine environment. And the international project Kogovšek is part of, called GoJelly, sees that as an opportunity. It believes it can tap these ethereal creatures to tackle another environmental scourge of our time: microplastic pollution. If successful, it will be a win-win.

A blooming problem

Jellyfish are among a select group of organisms that seem to thrive as humans trash Earth. Exactly why isn’t known, but one factor could be fewer competitors due to overfishing. Others may be the spread of jellyfish in ships’ ballast tanks, and the fact that jellies can live in oxygen-depleted, polluted waters. Whatever the causes, larger, more frequent jellyfish …