Microplastics ingested by marine worms threaten ocean biodiversity
Marine worms that are key food source for fish and birds eat less when they ingest plastic waste, and absorb pollutants they pass up food chain
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.
Microplastics can be made from polyethylene, polyethylene terephthalate, PVC or polystyrene. They are too small to be captured through existing wastewater treatment processes and wash straight into the ocean.
They fall into three categories: The raw material called "nurdles" that are melted down to make larger plastic items or used as exfoliating beads in cosmetic products, or larger pieces of plastic that have degraded and broken down into smaller particles over time. Microplastics are also found as fibres and have been traced back to synthetic textiles like polyester that are used to make clothes, which can release up to 1,900 tiny fibres per garment every time they are washed.
Microplastics carry a complex mix of chemicals which have the potential to harm the worms, the research showed. Many plastics contain chemical additives, such as plasticisers, dyes and antimicrobials, which can leach out into sediments and seawater. Microplastics also concentrate water-borne chemicals on their surfaces, such as pesticides.
There has been much campaigning around the impact of larger marine plastic pollution, with widely documented instances of fish and bird entanglement, ingestion and suffocation. But particles of this microscopic size are available to a much broader range of marine organisms, which ingest and retain these tiny plastic particles and act as prey for larger species.
The first study, by Stephanie Wright from the University of Exeter, put worms into laboratory tanks of varying levels of plastics contamination for up to one month, measuring their growth, physiology, survival and ability to gain weight. She found that lugworms feeding in sediment that was highly contaminated with microplastics put on less weight than worms in clean sediment and had less energy to invest in key processes such as growth and reproduction. These effects could cause populations to decline, the paper found.
Reduced feeding also means the sediment is being reworked less, the research found. The condition of the sediment could fall, leading to a decline in the communities which live in it. Wright said: "If worms in contaminated environments were to reduce feeding levels by an amount comparable to that seen in the lab, it would mean significantly less turnover of sediment."
"We believe our study has highlighted the need to reduce the amount of plastic waste and therefore microplastics which enter our seas," said another University of Exeter academic, Professor Tamara Galloway. "Plastics are enormously beneficial materials. However, if marine plastic pollution continues to increase, impacts such as those demonstrated in our laboratory studies could occur in the natural environment. It is therefore important that we prevent the accumulation of plastic and microplastic debris in marine habitats through better waste-handling practices and smarter choices in the materials we use."
A separate report, from Dr Mark Anthony Browne on work performed at Plymouth University, showed microplastics can transfer harmful chemicals to lugworms, including hydrocarbons, antimicrobials and flame retardants. Due to its role as a prey species, lugworms could pass these chemicals up the food chain to top predators such as fish.
"These chemicals are persistent, meaning they could accumulate in the tissue of organisms and take a long time to break down," said Professor Richard Thompson of the school of marine science and engineering at Plymouth University, who was project leader for the work. "Our laboratory studies provide the first clear evidence that microplastics could cause harm and show that this could result from both the physical presence of ingested plastic and chemical transfer. Our next steps will be to establish the full implications of these findings for organisms in natural habitats."