An expedition by the German research vessel Polarstern has unexpectedly unearthed unpleasant findings: Scientists have found high concentrations of microplastics in algae of the species Melosira arctica, which grows under sea ice. The algae apparently accumulates the particles to such an extent that their concentration is ten times higher than in the surrounding seawater. Scientists from the Alfred Wegener Institute for Polar and Marine Research (AWI) had taken samples of seawater and algae from ice floes.

The researchers warn in the journal "Environmental Science and Technology" that this poses a particular threat to marine life that feeds on the algae. "The filamentous algae have a slimy-sticky texture, so they may be collecting microplastics from atmospheric precipitation, the seawater itself, the surrounding ice, and any other source they encounter," explained Deonie Allen from the University of Canterbury and Birmingham University, who is part of the team.

In the spring and summer months, the Melosira algae grows rapidly under the sea ice, where it forms meter-long cell chains. When the algae contaminated with microplastics die and the ice to whose underside they adhere melts, they stick together to form lumps. These can quickly sink to the bottom of the Arctic deep sea.

"We have finally found a plausible explanation for why we always find the largest amounts of microplastics in deep-sea sediment in the area of the ice edge," emphasises AWI biologist Melanie Bergmann. The algae are an important food source for the bottom-dwelling animals and bacteria, it said.

Reports like these show how much the sea is already polluted by human garbage, even in remote areas – and that the interrelationships are often more complex than expected. Recently, researchers had shown that plastic waste in the sea can even cause entire ecosystems to reshape or even recreate: In the Great Pacific Garbage Patch, an oceanic vortex north of Hawaii in which garbage such as lost cargo, nets and tiny plastic particles collect, they had discovered crabs, snails and other marine organisms that actually only occur on the coasts – because they need solid ground. But the artificial plastic world in the sea offers them exactly that: And so a habitat is created on the high seas that would not have existed without human activity.

What may sound nice at first glance – after all, this is how living beings find a new, albeit artificially created habitat – can have devastating effects on natural ecosystems. This is because the newcomers can displace the original inhabitants of the high seas or disrupt the food webs.

In the case of Arctic algae, which accumulate plastic particles, the consequences are difficult to assess: they are far down in the food chain. The plastic particles will therefore foreseeably find their way from algae to algae eaters to marine predators.

Inflammation in the gastrointestinal tract

It is slowly becoming clear that this will probably not be without consequences for birds, predatory fish and marine mammals. Just recently, scientists at London's Museum of Natural History published a study on seabirds diagnosed with "plasticosis," an inflammation caused by the direct and indirect consumption of microplastics.

Whether the plastic particles in marine organisms also pose a danger to people who eat fish, seafood or algae has so far been controversial.