Caprella mutica is a slender amphipod crustacean, 15–30 mm long, with an elongated body and grasping pereopods that it uses to cling to filamentous substrates. Native to the Sea of Japan, it was first recorded in European waters in the 1990s and has since spread to aquaculture sites from Norway to the Bay of Biscay — likely via hull fouling and equipment transfers. It thrives on fouled net surfaces, ropes, and pontoons, often reaching densities of several thousand individuals per square metre by late summer.
While skeleton shrimp do not cement to surfaces like barnacles, their sheer abundance creates problems. Dense colonies, combined with the mud tubes and detritus they accumulate, clog net meshes and measurably reduce water flow. The animals also attract predators — juvenile fish may ingest Caprella and associated debris — and their presence on harvested shellfish downgrades product appearance. Farms near harbours and marinas tend to experience the worst infestations, since these sites act as reservoirs for the species. Check the farm map to see which areas report high Caprella densities.
Population crashes occur naturally in winter when temperatures drop below 5–6 °C, but between June and October management is necessary. Air-drying kills Caprella within hours, and freshwater immersion for 30–60 minutes is equally effective. Regular net changes during the summer peak remove accumulated colonies. Because Caprella is a secondary fouler — it colonises surfaces already covered by hydroids or algae — controlling those primary foulers also suppresses skeleton shrimp numbers. See the methods comparison for integrated approaches.
Control Methods
Air-drying Freshwater treatment Regular net changes