Rapid treatment of vessels fouled with an invasive polychaete, Sabella spallanzanii, using a floating dock and chlorine as a biocide

Chlorine solution was added to the water encapsulated within a proprietary ‘floating dock’ to treat a vessel infested with the invasive polychaete Sabella spallanzanii. The chlorine was added as sodium dichloroisocyanurate (‘dichlor’) at an initial concentration of 200 mg l⁻¹ of free available chlorine (FAC). This concentration killed 99% of S. spallanzanii in their tubes during a 4-h exposure in laboratory tests (EC₉₉ 160 mg FAC l⁻¹). The concentration of FAC in the floating dock declined to ~50 mg l⁻¹ after 4 h and < 10 mg l^–1 after 16 h. Residual FAC was neutralised with thiosulphate at completion of exposure. A sample of 30 S. spallanzanii individuals collected from the hull after treatment all showed morphological damage and 28 showed no response to touch. Re-examination of the hull after 6 d found no live worms or other fouling organisms. This method provides a cost-effective, rapid means of treating hull fouling.