Fragments of microplastics are readily incorporated into groups of microscopic algae, altering the rate at which the plastics move through seawater, a recent study has found. In laboratory tests, polystyrene microbeads, which usually sink to the bottom of seawater at a rate of 4 mm a day, sank at a rate of several hundreds of metres a day when part of microalgae aggregates.

This study suggests that microalgae aggregates could be responsible for transporting microplastics into the deep ocean. They may also be the reason that other studies have found surprisingly few microplastics in surface waters and high concentrations in the seabed. Worryingly, as marine snow (decaying organic matter, including microalgae aggregates, which falls from the ocean surface to the seafloor) is the main source of food for many marine creatures, they could be exposed to increased levels of microplastics.

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