A collaborative project involving MacLab, Cawthron, Port Nelson and Moananui is seeing Green Shell Mussels (GSM) grown off one of the port’s wharves to improve water quality in the wider Nelson haven. 

Shannon Holroyd, Port Nelson’s Environment Manager, says the prompt was her CEO, Hugh Morrison, sending her an article about similar projects in Auckland’s Viaduct Basin. These saw 38 seeded mussel lines attached to public space on an inner city wharf, as well as mussels being reseeded to improve water quality in the Hauraki Gulf. 

Port Nelson, MacLab, and Cawthron are partners in the Moananui blue economy cluster. Moananui serves as the national centre for blue economy innovation and high-value creation, fostering collaboration, knowledge exchange, and access to innovation opportunities to accelerate responsible development within the maritime sector.  

The entities developed a proposal for the Living Filters project, a first stage six-month trial to put GSMs into the port. It won some funding from the Sustainable Seas Fund. MacLab supplied nearly 29,000 juveniles for two frames, which were hung in sleeves off a port wharf in January. 

Shannon says they’d grown between 8-11mm when first looked at 6 weeks later.  

Cawthron has installed data loggers and samplers to monitor a range of factors including, water temperature and the presence of heavy metals and hydrocarbons.  

Being sited on the estuary of the Maitai River brings heavy metals off rooves, hydrocarbons and other urban runoff. Boat maintenance activities such as painting and cleaning ships also contribute to the presence of heavy metals and hydrocarbons, which it’s hoped the mussels may reduce by filtration (also called ‘bioremediation’). 

“Largely, however, we want to improve the clarity of the water,” says Shannon. 

“When fully grown each of these mussels have the ability to filter up to 200 litres each per day. Meaning altogether they  could potentially filter 5,76 million litres per day.” 

Cawthron is also getting data on how often the mussels open and close (gaping behaviour) which can indicate feeding and filtering behaviours, and the presence of stressors such as a freshwater event, predators, or toxic algae, for example.   

In March, Port Nelson had an Open Day, and the GSM project was among the attractions for more than 2,000 visitors. Cawthron and port staff were on hand to demonstrate what was being done. 

Cawthron brought along their ‘mobile living lab’ setup to demonstrate mussel’s filtering ability, with gaping sensors. 

It also had heart rate monitors attached to real live mussels on show. “You could see the mussels’ heartbeat,” says Shannon. 

And for those who’ve never seen a mussel’s heartbeat, what does it look like? 

“It’s very similar to ours but much slower.” 

Cawthron is hoping the outcome of the six-month trial at Port Nelson may provide a blueprint for wider use at ports. They also hope this study will stimulate thinking toward greater restorative programmes on urban coasts. 

Shannon Holroyd says Port Nelson is very open to much wider use of them to improve water quality and clarity. 

“There’s a lot of area under our wharves where we could just let them go.”