Mussell 'cages' deployed in a pilot project to help stem the flow of marine plastics
Scientists from Plymouth Marine Laboratory (PML) have installed cages filled with mussels at three Yacht Havens sites as part of a trial project to establish how effectively they can remove microplastics from tidal, estuarine waters.
Earlier laboratory experiments conducted by the PML team using a custom-designed flume tank have shown that a cluster of 300 blue mussels (Mytilus edulis) - around 5kg - could filter out over 250,000 microplastics per hour.
This is achieved by harnessing the natural filtering power of the mussels, which get their food by filtering seawater, sieving out plankton and other nutritious particles and flushing out unwanted particles from their digestive systems. As part of this process, microplastics are ejected in their normal faecal matter – which can then be collected as it sinks.
Mussel Cage locations:
Nature-based solutions to stem marine plastics
A scaled mussel filtration reef/system would not only remove microplastics but have multiple other benefits. The humble mussel’s hardy nature and water filtration capabilities mean they can improve overall water quality, reduce pathogen numbers and soak up pollution while increasing local biodiversity and seafood quality in a given area.
With technical support from PML Applications (PML’s commercial subsidiary) the specially-designed cylindrical PML ‘cages’ (which were constructed by Flint Engineering Solutions Ltd), currently being deployed contain 50kg mussels and feature receptacle tubes to collect the filtered waste. This enables the scientists to collect the faeces - and the microplastics - which can then be hauled in and removed from the seawater.
“An estimated eight million tonnes of plastic end up in the ocean every year – that’s the equivalent to a full truckload dumped into the sea every minute.”
“Through lab-based experiments and early trials we have shown that mussels could play a valuable role in helping to extract microplastics – effectively collecting up and leaving the recycling out for us to then dispose of. We are incredibly excited to see how well these new custom-made cages will work and very grateful to Yacht Haven Marinas Group for their support.”
- Professor Pennie Lindeque, Head of Science - Marine Ecology and Biodiversity.
Scaling up the theory
The organisation’s computer modelling has indicated that mussels sited near the mouths of rivers and estuaries could filter between 20-25% of small, waterborne microplastics. The factors are complex, with physical parameters to consider including depth, currents, tides, temperatures and varying plastic supply. However, the findings suggest that a mussel-based clean-up system deployed closer to the source of microplastics e.g. waste water treatment works or storm water drains could potentially be rolled out at scale with significant positive effects.
The theory is now being scaled up to testing it in selected locations around the River Plym. Cages have been anchored under pontoons at Plymouth Yacht Haven, Yacht Haven Quay and Turnchapel Wharf and they will be collected at the start of 2023 before being analysed.
Steve Kitchen, marina director at Plymouth Yacht Haven, said “Having installed a Seabin in the marina earlier this year, it’s highlighted that issue regarding plastics in the water. Although we’ve been able to collect larger pieces of marine waste through our Seabin, we were delighted to offer our facilities to this project to help research how microplastics can be safely captured and removed from our waters”.
Steve stated how this new research project is one of many taking place in Britain’s Ocean City right now. “In the past 12 months, we’ve partnered with various local organisations to run workshops with our customers and local school children to raise awareness around these issues. The team behind the autonomous Waste Shark vessel ran a demonstration on-site this summer, and the LIFE Recreation ReMEDIES Seagrass project in Plymouth Sound has led to a huge amount of carbon being captured with a no anchor zone being well-observed by resident and visiting boaters.”
About Plymouth Marine Laboratory
A world leader in the field of marine research, Plymouth Marine Laboratory (PML) is a charity committed to the delivery of impactful, cutting-edge environmental and social science in support of a healthy and sustainable ocean.
Alongside the University of Plymouth and Marine Biological Association, PML is part of Marine Research Plymouth, the UK’s largest cluster of marine science researchers.
PML’s commercial subsidiary, PML Applications, provides research, consultancy and services for the marine and maritime sector.