The presence of microplastics in the ocean is a growing concern, but there's still a lot we don't know about how marine organisms interact with them. A new study from Plymouth Marine Laboratory and the University of Exeter shows how the behaviour of animals living in sediment can affect the fate of this microplastic pollution.
The team of researchers, led by PML's Dr Rachel Coppock, wanted to investigate whether some of these creatures around our coasts might actually be burying microplastics deeper into the sediment, locking it away from the open water where it is unlikely to degrade.
By taking samples from across Plymouth Sound and carrying out experiments in the lab, they were able to observe how different species behaved in ways that led to plastics being buried or potentially resuspended back into the water.
Certain animals were acting as "conveyers", moving sediment grains and microplastics up and down through the sediment whilst carrying out activities such as feeding and burrow construction, whereas animals that simply mixed the sediment or carried it solely upwards were less likely to contribute to plastic burial and may instead resuspend the microplastics back into the water column. Overall, however, these animal communities contributed to a net burial of microplastics.
The researchers could see how these animals were having an effect on the fate of microplastics, but how might this be affecting the animals? In experiments, starfish-like brittle stars were shown to bury nylon fibres, but interactions with these microplastics also changed their behaviour, reducing the amount they mixed the sediment deep in their burrows. Sediment mixing is a vital ecological process that provides oxygen and nutrients to this important marine environment.
Dr Coppock, who led the study as part of her PhD with PML and the University of Exeter, said: "This study shows us that marine animals are burying plastic in biodiverse and functionally important coastal seabed habitats, where it is likely to stay locked away for potentially thousands of years. We're all aware of the need to reduce the amount of plastic entering the sea, but this really highlights how long-term the effects of our actions now are likely to be. A reduction in plastic waste, coupled with developing properly biodegradable plastics would make a huge difference."