This oyster farm in Baie de Morlaix, northern Brittany, cultivates Pacific oysters (Crassostrea gigas) on intertidal iron trestles across a 4-hectare concession, producing approximately 180 tonnes per year. The dominant fouling problem at this site is the invasive slipper limpet (Crepidula fornicata), a filter-feeding gastropod that forms stacking chains on oyster shells and mesh bags. At peak infestation, slipper limpets constituted up to 30 percent of total bag weight, reducing water circulation within bags, competing with oysters for phytoplankton, and significantly increasing handling time during grading and sorting operations.
In collaboration with the local shellfish research centre (IFREMER Morlaix), the farm trialled a thermal treatment protocol using a purpose-built hot water unit mounted on a tractor-drawn trailer that could operate directly on the foreshore during low tide. Bags were passed through a 55-degree-C water bath for 10 seconds — a temperature-duration combination identified in preliminary laboratory trials as lethal to Crepidula but survivable for oysters. Field results over two treatment seasons confirmed the laboratory findings: slipper limpet mortality exceeded 95 percent per treatment, while oyster mortality remained below 1 percent. Treated bags showed 25 percent faster oyster growth over the three months following treatment, attributed to reduced competition for food and improved water circulation. The treatment cost, including equipment amortisation, was approximately 0.02 euros per oyster — roughly one-fifth the cost of manual removal.
The slipper limpet and other gastropod foulers are profiled in the organisms database. This farm site is shown on the aquaculture farm map with regional fouling data. The solutions comparison tool evaluates thermal treatment alongside other shellfish anti-fouling methods, and the cost calculator can model the return on investment for thermal treatment equipment.
Outcomes
Slipper limpet (Crepidula fornicata) identified as the dominant fouler — up to 30% of bag weight. Hot water treatment at 55 degrees C for 10 seconds killed limpets without harming oysters. Treated bags showed 25% faster oyster growth over the following 3 months.