6 minute read
Nicki Holmyard
BY NICKI HOLMYARD
Tackling tube worms
A new study aims to fi nd an early warning for worm infestation
Iam always amused when people looking to come into the mussel industry think it will be easy. A� er all, don’t you just put a few ropes in the water and haul in a crop of black gold a year or two later? If only it was that simple!
The reality is that there are many technical and biological hurdles to overcome in order to get a successful crop to market, year a� er year, any of which can throw fi nancial forecasts into disarray. And that is without taking into account “curve balls”, such as Covid-19 and Brexit, causing severe disrup� on to marke� ng plans.
In taking our own mussel farm (www.off shoreshellfi sh.com) off shore, we have faced many such hurdles, and we s� ll have a lot to learn about the dynamics of farming on a large scale, six miles out in the open sea. However, it has meant that we can grow a crop from spat to harvest, in just over one year, which is a big advantage when compared to our previous sites in Scotland, where it took between two to three years to achieve the same thing.
Another advantage is that we no longer have an issue with biofouling organisms growing on the shells, such as barnacles (Balanus sp.) and tube worm (Pomatoceros triqueter). However, we do have occasional plagues of starfi sh, which se� le around the same � me as the mussels, and quickly outgrow them by feeding voraciously, leaving us staring at a devastated crop.
In Scotland and Shetland, tube worm can be a major problem in some years, with an es� mated 500 tonnes of mussels spor� ng the calcareous white worm casts on their shells, causing fi nancial losses of around £500,000 per year. As produc� on increases, the losses will also stack up.
“On some of our sites, we have found as much as 20% of the shells aff ected. It’s seasonal, it’s not every year, and some� mes it is worse than others, but it can be a big problem and results in considerable wastage,” said Michael Tait, MD of Shetland Mussels.
Tube worm do not harm the mussels, but they are virtually impossible to remove, make the product less desirable to customers in terms of aesthe� cs and smell when cooked, and they can also damage vacuum packaging.
A new project, led by the University of S� rling’s Ins� tute of Aquaculture, with support from Shetland Mussels and the Sustainable Aquaculture Innova� on Centre (SAIC), aims to develop a rapid diagnos� c tool for the presence of P. triqueter DNA in plankton and shell swab samples. Such a tool would enable producers to make informed decisions about dealing with tube worm, including environmental management and cleaning regimes.
Similar molecular diagnos� c techniques are already common in fi nfi sh farming, but not in the shellfi sh sector. The project could therefore herald a signifi cant step change for shellfi sh farmers, enabling them to improve stock management and product quality.
Currently, the only way to detect the presence of larval tube worm is by looking at a water sample under a microscope, but as project lead researcher Dr Stefano Carboni explained, the larvae can be easily confused with other organisms, and sampling only covers a small volume of water.
“Tube worm and other biofouling are of long-standing concern for the shellfi sh industry, and there is not a clear understanding about what drives the se� lement of larvae. A more prac� cal and reliable method for iden� fi ca� on, would be an invaluable development for the industry, and it could be applied on a global scale. Once we have a molecular diagnos� c tool, it could easily be adapted to iden� fy other organisms of interest, including the D larvae of mussels, which would take all the guess work away from shellfi sh farmers,” he said. Current strategies for dealing with early-stage tube worm se� lement include Left: Mussels infested with barnacles Opposite: Mussel shell with tube worm; Scallop shell with tube worm
monitoring water temperatures and weather pa� erns to es� and weather pa� erns to es� mate when it will occur, exposing mate when it will occur, exposing shells to the air, washing them, or shells to the air, washing them, or cleaning using ace� c acid, brine or hot cleaning using ace� c acid, brine or hot water. None of these are cost-eff ec� ve water. None of these are cost-eff ec� ve and can have a detrimental eff ect on growth and can have a detrimental eff ect on growth and survival.
For Michael Tait, who maintains separate For Michael Tait, who maintains separate spat collec� on and ongrowing sites, a detecspat collec� on and ongrowing sites, a detec� on tool could allow him to delay retubing � on tool could allow him to delay retubing seed mussels onto new lines un� l tube worm seed mussels onto new lines un� l tube worm larvae are no longer registering in an area.
“This project has exci� ng poten� al to change the way mussel farms are managed in future, and it will be interes� ng to see the ini� al results. The poten� al for adapta� on to a tool that iden� fi es mussel larvae would also be of interest to us,” said Tait.
Regular water samples will be collected from Shetland Mussels, along with surface swabs from mussel shells, which the S� rling University team will analyse for the presence of tube worm DNA. The data will allow them to monitor pa� erns and seasonal varia� ons that could inform cleaning schedules and poten� al site selec� on, as well as preven� ng future losses.
Heather Jones, CEO at SAIC, was pleased to support a project to help the growing Sco� sh shellfi sh sector.
“This project represents just one example of pioneering research that will support further sustainable growth to meet the global demand for protein. New data-led techniques such as this DNA diagnos� c tool can help to drive the en� re industry forward, with benefi ts spanning the environment, businesses opera� ng in the sector, and the end consumer,” she said.
A similar project is currently underway in Sweden, where mussel farming company Bohus Havsbruk and the Swedish environmental ins� tute IVL, are looking at how mussels can be heat treated to remove fouling.
The research, which is part of the EU Horizon 2020 AquaVitae project, is trialling the exposure of mussels to seawater at a higher temperature than the surrounding sea, for a short period of � me.
Trials are currently s� ll in the laboratory phase, with researchers inves� ga� ng the temperature range that will result in high worm mortality, while maintaining high mussel survival. Once this has been established, the next stage is to undertake fi eld trials to ascertain the feasibility of working at scale. FF
