Watersipora subtorquata forms thick, encrusting colonies with a distinctive orange-red to dark rust colour, making it easy to identify among the pale-coloured bryozoans more typical of European fouling communities. Colonies grow as irregular sheets 2–5 mm thick, with zooids about 0.6 mm long arranged in radiating rows. Originally from the southern hemisphere, this species has spread through international shipping and now occurs in the Mediterranean, along the Atlantic coast from Portugal to Ireland, and increasingly in southern British waters.
What makes Watersipora stand out is its resistance to copper. Most copper-based anti-fouling coatings effectively suppress barnacle and mussel settlement, but Watersipora larvae tolerate copper concentrations that kill other organisms. On copper-treated cage nets and pontoons, this gives the red-rust bryozoan a competitive advantage — it colonises surfaces from which other foulers are excluded, sometimes becoming the dominant species on treated infrastructure. This undermines the effectiveness of copper coatings and creates a platform for secondary foulers to establish on top of the bryozoan crust. The FAQ section covers more on copper resistance and regulatory trends.
Mechanical scraping and high-pressure washing remove established colonies, though the encrusting base can be difficult to clear completely from textured surfaces. Silicone foul-release coatings perform better against Watersipora than copper because they prevent strong adhesion regardless of the organism’s copper tolerance. Farms in areas where this species has been recorded should factor its copper resistance into their anti-fouling strategy. Browse other bryozoan foulers — including Membranipora and Bugula — in the organisms database.
Control Methods
Mechanical scraping Anti-fouling coatings High-pressure washing