Microplastics ingested by marine worms threaten ocean biodiversity

Tiny bits of plastic rubbish ingested by marine worms are significantly harming their health and will have a wider impact on ocean ecosystems, scientists have found.

Microplastic particles, measuring less than five millimetres in size, have been accumulating in the oceans since the 1960s and are now the most abundant form of solid-waste pollution on earth.

Two UK-based studies published in the journal Current Biology looked at whether these near-invisible, microscopic plastics that sink into mud and sand in high concentrations are causing harm to species at the base of the food chain that ingest this sediment during feeding, and play a key ecological role as a source of food for other animals.

Using the lugworm as an indicator species, the first study, by the University of Exeter, found that worms feeding in highly contaminated ocean sediment ate less and had lower energy levels. The second study, by Plymouth University, established for the first time that ingesting microplastics can transfer pollutants and additives to worms, reducing health and biodiversity.

Ingestion of microplastics by species at the base of the food web is a cause for concern as little has been known about its effects until now. Many other organisms that have a similar feeding behaviour, such as starfish, sea cucumbers and fiddler crabs, may be similarly affected.

Lugworms are common invertebrates widely found across the whole of the north Atlantic, living in burrows in the sand of beaches. They eat sand particles, digesting any micro-organisms and nutrients and passing the sand as waste through their tail, leaving a distinctive trail or "cast" on the beach. The worm can make up about 30 per cent of the biomass of an average sandy beach, making it an important source of food for wading birds and flatfish.

The "earthworms of the sea", lugworms provide another important ecosystem service by turning over large volumes of sand, replenishing organic material and oxygenating the upper layers to keep the sediment healthy for other animals and micro-organisms to thrive in.