Bugula neritina forms erect, bushy colonies up to 100 mm tall, with a dark purple-brown colour and a distinctive spiral branching pattern. Each branch consists of rows of box-shaped zooids about 0.8 mm long. Colonies are flexible and sway with the current, which distinguishes them from the rigid encrusting growth of hard bryozoans like Membranipora. B. neritina is cosmopolitan in warm-temperate and subtropical waters and is common throughout the Mediterranean, along the Atlantic coast from Portugal to Ireland, and in sheltered harbour environments further north.
Bugula colonies trap silt and fine detritus within their branching structure, effectively creating a sediment blanket across net panels. This reduces mesh openness and water flow, which in turn lowers dissolved oxygen inside fish cages. A single colony is light, but dozens per square metre add up — particularly when combined with other soft foulers like hydroids and tunicates in the mixed communities typical of Mediterranean farms. The resulting drag increase shortens the interval between cleaning cycles and raises overall production costs.
Bugula larvae (coronate larvae) are short-lived and settle within hours of release, often close to the parent colony — which is why infestations tend to be patchy but locally intense. Air-drying for 6–12 hours kills colonies, and freshwater immersion for 1–2 hours is equally effective. Anti-fouling coatings reduce larval settlement, especially during the peak summer breeding season. For a full comparison of soft-fouling control strategies, visit the methods comparison page. Other bryozoan foulers are profiled in the organisms database.
Control Methods
Air-drying Freshwater immersion Anti-fouling coatings Manual removal