ABSTRACT
Water treatment officials in the southern New Zealand city of Dunedin have had to cope since 1996 with heavy and pernicious infestations of brown ‘weeds’. The freshwater bryozoans Paludicella articulata (Ehrenberg, 1831) and Plumatella repens (Linnaeus, 1758) grow on hard surfaces, in water intake pipes, on floats, and throughout the microstrainer hall at Southern Reservoir and the associated water treatment station in Dunedin. Their presence has intermittently affected normal operation of the plant, particularly when clumps are torn off the sides of pipes and walls, clogging microstrainers and filters, sometimes causing considerable damage. Bryozoans living in pipes may also reduce effective pipe bore diameter, increasing friction and thus slowing water velocities. The presence of fouling bryozoans increases workloads, reduces efficiency, and has impeded the delivery of drinking water to Dunedin residents.
