This operation runs three traditional wooden rafts (bateas) in Ria de Vigo, northwest Spain, producing approximately 450 tonnes of Mediterranean mussel (Mytilus galloprovincialis) annually. The nutrient-rich upwelling waters of the Galician rias support exceptionally fast mussel growth but also drive intense biofouling. The dominant foulers at this site are barnacles (Balanus perforatus), colonial sea squirts (Ciona intestinalis), and increasingly, invasive Pacific oyster (Crassostrea gigas) spat that settles on mussel ropes and competes for space and food.
The farm implemented a structured management programme combining two established techniques: periodic air-drying and systematic thinning. Mussel ropes are lifted clear of the water for 48-hour air exposure every 4 weeks during the May-to-November fouling season, killing soft-bodied tunicates through desiccation while the robust mussels survive. This protocol reduced tunicate coverage by 80 percent over the trial period. Combined with thinning operations — where mussel clusters are stripped from ropes, sorted to remove foulers, and re-sleeved at lower density — the farm achieved a 15 percent increase in marketable yield and a measurable improvement in mussel size uniformity at harvest, both of which translated to higher per-kilogram prices at the processing plant.
The Galician ria system is mapped with fouling intensity data on the aquaculture farm map. Tunicate and barnacle species found at this site are documented in the organisms database. The solutions comparison tool evaluates air-drying alongside other shellfish anti-fouling methods, and the cost calculator can estimate the economic return from implementing combined drying and thinning protocols.
Outcomes
Dominant foulers: barnacles, sea squirts (Ciona), and Pacific oyster spat. Air-drying ropes for 48 hours every 4 weeks reduced tunicate cover by 80%. Combined with thinning, overall marketable mussel yield increased by 15%.