Air Bubble Curtain

Air bubble curtain systems use perforated pipes or diffuser hoses installed around the bottom perimeter of cage structures to release a continuous wall of rising air bubbles. These bubbles create localised turbulence and upwelling currents that physically interfere with planktonic fouling larvae — barnacle cyprids, mussel pediveligers, hydroid planulae — as they drift toward the net surface to settle. The disturbance makes it harder for larvae to detect chemical settlement cues on the mesh and disrupts their ability to attach securely.

A secondary benefit is oxygenation. The rising bubbles draw oxygen-depleted bottom water upward and increase dissolved oxygen levels inside the cage, which benefits fish health and feeding behaviour — particularly in sheltered, low-current sites where stratification can trap deoxygenated water at depth. Some Norwegian farms have reported 15-25% reductions in early-stage fouling settlement on nets protected by bubble curtains, though effectiveness drops in exposed sites where natural currents already provide strong water mixing. The farm map highlights which CRAB project sites have trialled this approach and under what conditions.

As a standalone method, air bubble curtains are insufficient for heavy fouling environments. Their real value lies in combination with other techniques — reducing initial settlement rates so that subsequent mechanical cleaning or foul-release coatings face a lighter fouling load. Compressor energy and maintenance costs are moderate; the cost calculator can model these against expected fouling reduction for your site parameters. The methods comparison page scores bubble curtains alongside all other physical and biological approaches to help determine where they fit in an integrated strategy.