New research into mussel broken shell problem

A group of aquaculture researchers in Scotland is undertaking an initiative that could determine the cause of shell breakage in different species of mussels, a problem seen as one of the biggest challenges facing the sector globally.

The consortium – comprising of the University of Stirling’s Institute of Aquaculture, Fassfern Mussels, the Scottish Shellfish Marketing Group, The Fishmongers’ Company, the Association of Scottish Shellfish Growers, and the Sustainable Aquaculture Innovation Centre (SAIC) – will examine a range of factors that could lead to weakness in mussels’ shells.

Trialling different conditions among different species at two Scottish sites, the researchers will aim to determine whether shell strength is related to mussels’ genetics; environmental conditions, such as the salinity of local water; or the harvesting process itself.

Salinity, for instance, can affect the mineral properties of water and, in cases where it is too low, could compromise shell strength. Certain species of mussels – and hybrids thereof – are also suspected to have weaker shells to begin with; specifically, bay mussels or Mytilus trossulus.

In Scotland, shell breakage causes mussels to be unusable and is estimated to cost the sector around 2% of its average annual output, as well as associated costs. In extreme cases, it can prevent farmers from harvesting or cause sites to completely shut down.

The researchers will combine cutting-edge molecular tools and biomaterial testing during the project. Depending on the results of the initial phase of the study, the project could develop a molecular tool that will assess juvenile mussels for shell strength, a location screening system for mussel farms, or a new process for harvesting.

Dr Stefano Carboni from the University of Stirling’s Institute of Aquaculture said: “We are aiming to understand what causes a large problem for the sector. Our project will help producers to understand whether the strength of mussels’ shells is genetic, influenced by local environmental conditions, the harvesting process itself plays a part, or it is a combination of all these factors. Whatever the causes, we can help farmers avoid growing mussels for years only to realise there is a problem at the last moment.

“Once we have determined the variables, we can start to develop remedies – that might be screening for salinity conditions or a tool that predicts the percentage of mussels that will develop broken shells. From there, we can protect jobs, create new products, and develop a more efficient and sustainable sector.”

Heather Jones, CEO at SAIC, said: “The mussel sector is a growing part of Scotland’s aquaculture landscape, providing sustainable jobs in rural and remote communities. Shell breakage is among the biggest challenges to its growth and tools that can better inform how the sector grows mussels, selects sites, and undertakes harvesting will be invaluable in supporting development. It is a great example of how organisations with a common interest in shellfish can collaborate to develop new technologies and methods that could make a real difference to the sector.”

Dr Nick Lake, CEO of the Association of Scottish Shellfish Growers, added: “The wild blue mussel is a valuable natural resource within Scotland, which in recent years has supported the development of a dedicated cultivation industry. While around 8,000 tonnes are currently cultivated, plans are in place to increase this to around 20,000 tonnes, creating significant additional employment.

“To ensure we have a sustainable basis upon which to develop, there is a requirement to understand the detailed biology of the natural populations and environmental conditions allowing the shellfish to thrive. By harnessing the advanced scientific techniques available through the Stirling University research group, we hope to rapidly unlock the answers to some of the fundamental questions regarding the selection of natural blue mussel stocks which are optimal for cultivation in Scotland.”