Shellfish
BY NICKI HOLMYARD
Tackling tube worms A new study aims to find an early warning for worm infestation
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am 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 financial 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.offshoreshellfish.com) offshore, 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 starfish, 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 financial 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 affected. 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
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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 finfish farming, but not in the shellfish sector. The project could therefore herald a significant step change for shellfish 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 shellfish 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�fica�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 shellfish 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
www.fishfarmermagazine.com
12/07/2021 15:48:49
