Metridium senile is a soft-bodied anemone with a tall, columnar body reaching 100–150 mm in height, topped by a crown of hundreds of fine, feathery tentacles. Colour ranges from white and orange to brown. The animal attaches to hard surfaces via a muscular pedal disc and can slide slowly or reproduce asexually by pedal laceration — tearing off small tissue fragments that regenerate into new individuals. Metridium is common in cold-temperate waters from Norway and Iceland through the North Sea to the northern Atlantic coasts of the UK and Ireland, usually from the low intertidal to 100 m depth.
Plumose anemones colonise cage frames, pontoon crossbeams, mooring chains, and other rigid structures rather than the net panels themselves. While they add less biomass per unit area than mussels or barnacles, colonies of 20–50 individuals on a frame member increase drag and add weight that accumulates over multi-year deployment periods. More practically, dense Metridium growth obscures structural components during underwater inspections, making it harder to spot corrosion or fatigue cracks on steel and composite frames. For farms using ROVs or divers for inspection, clearing anemone growth adds time and cost — the cost calculator can help quantify this.
Manual removal is straightforward: the anemone detaches with moderate force. However, any tissue left behind can regenerate, so thorough scraping is needed. Air-drying kills individuals within a few hours. Regular cleaning of frames and chains during scheduled maintenance keeps populations low. Because Metridium is a slow grower and a minor contributor to net fouling, it is typically addressed as part of a broader integrated management programme rather than targeted specifically. Learn more about cold-water fouling species in the organisms database.
Control Methods
Manual removal Air-drying Regular net changes